Systems Engineering of Phased Arrays [1 ed.] 9781630814892, 163081489X

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Systems Engineering of Phased Arrays

Systems Engineering of Phased Arrays Rick Sturdivant Clifton Quan DISCLAIMER OF WARRANTY

Enson Chang

The technical descriptions, procedures, and computer programs in this book have been devel­ oped with the greatest of care and they have been useful to the author in a broad range of applica­ tions; however, they are provided as is, without warranty of any kind. Artech House, Inc. and the author and editors of the book tided Systems Engineering ofPhased ATTays make no warranties, expressed or implied, that the equations, programs, and procedures in this book or its associated software are free of error, or are consistent with any particular standard of merchantability, or will meet your requirements for any particular application. They should not be relied upon for solving a problem whose incorrect solution could result in injury to a person or loss of property. Any use of the programs or procedures in such a manner is at the user's own risk. The editors, author, and publisher disclaim all liability for direct, incidental, or consequent damages resulting from use of the programs or procedures in this book or the associated software.

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-Rick Sturdivant

ISBN 13: 978-1-63081-488-5

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All rights reserved. Printed and bound in the United States of America. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Artech House cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark.

10 9 8 7 6 5 4 3 2 1

Clem and Delia Sturdivant

To my parents, Francis and Billie Quan,

my wife, Lily Quan, and my two boys, Jonathan and Austin, for their love, prayers, and support in my life

-Clifton Quan

To my loving wife,

Susan, and our cherished children, Sean, Tyler, and Jordan

-Enson Chang

Contents Preface

xvii

Acknowledgments

xxi

Part I System Engineering Activities

1

The Systems Engineering Process and Its Application to Phased Arrays

3

1.1

Introduction

3

1.2

Methodological Reductionism

4

1.3

The Systems Engineering Approach

6

1.4

The Three-Phase Process

7

1

1.5

Phase 1: Concept Development

1.5.1 1.5.2 1.5.3 1.5.4 1.5.5 1.5.6

Needs Analysis Alternacives Exploration Trade Studies and Baseline Selection New Technology Validation Risk Management Plan Other Concept Development Activities

vii

8

10 11

14 16 16 20

viii

Contents

Systems Engineering of Phased Arrays

1.6

Phase II: Engineering Development

20

1.6.1 1.6.2 1.6.3 1.6.4 1.6.5 1.6.6 1.6.7 1.6.8 1.6.9 1.6.10 1.6.11 1.6.12

Typical Engineering Activities for Phased Arrays Antenna Development Integrated Circuit Development T /R Module Development Thermal Design and Heat Transfer Development Beamformer Development Digital Receiver/Exciter Development Mechanical Structure Development Production Plan Development Acceptance Testing Other Functions Outputs from Engineering Development

21 21 21 22 22 22 22 23 23 23 23 23

1.7

Phase III: Post-Development

24

1.7.1 1.7.2 1.7.3 1.7.4

Production Deployment Operation and System Maintenance Eventual Decommissioning

24 24 24 24

1.8

Conclusions

25

1.9

Problems

25

References

25

2

Phased Array System Architectures

29

2.1

Introduction

29

2.2

Phased Array System Basics

33

2.3

Phased Array Architectures

40

2.3.1 2.3.2 2.3.3

40 41

2.3.4 2.3.5

Passive Phased Arrays AESA AESA with Phase Shifters at Each Element and at Each Subarray Element-Level Digital Beamforming Other Methods

2.4

Array Architectures for T /R Module Integration

48

2.5

to

Phased Array System Architectures

Array Beamforming Options

42 46 47

49

ix

2.6

Polarization Diverse and Wideband Arrays

51

2.7

Conclusions

51

2.8

Problems

51

References

52

3

Use Cases for Phased Arrays

55

3.1

Introduction to Use Cases

55

3.2

High-Altitude Platform Station

56

3.2.1 3.2.2

56

3.2.3

Introduction to HAPS HAPS System Description with Key Challenges and Benefits HAPS Examples and Summary

3.3

Medical Applications of Phased Arrays

60

3.3.1 3.3.2

60

3.3.3

Introduction to Medical Phased Arrays Medical Arrays System Description with Key Challenges and Benefits Medical Phased Array Examples and Summary

3.4

Phased Array for 5G MIMO Broadband

62

3.4.1 3.4.2

62

3.4.3

Introduction 5G Broadband Phased Arrays 5G Phased Array System Description with Key Challenges and Benefits 5G Phased Array Examples and Summary

3.5

Airborne Radar for Fighter Aircraft

65

3.5.1 3.5.2

65

3.5.3

Introduction to Military Phased Arrays Airborne Phased Array System Description with Key Challenges and Benefits Airborne Phased Array Examples and Summary

3.6

Conclusions

67

3.7

Problems

67

References

68

4

Phased Array Conce~t Develo~ment Exam~le

71

4.1

Introduction

71

57 60

61 61

63 64

65 66

Contents

Systems Engineering of Phased Arrays

X

xi

4.2

Needs Assessment- A Common Starting Point

72

5.10

Reflector Antenna

112

4.3

Technology Opportunities

73

5.11

Vivaldi Tapered Slotline Antenna

115

4.4

System Architecting

73

5.12

Low-Profile Vivaldi Tapered Slot Antennas

118

4.5

The SAI Method for New System Concept Development 74

5.13

Tightly Coupled Dipole Array

121

4.6

Application of the Modified SAI Method to Broadband Access for Small to Medium-Size Public Venues

5.14

Conclusions

122

75

4.6.1 4.6.2 4.6.3 4.6.4 4.6.5 4.6.6

Step 1: Determine Value Proposition and Constraints Step 2: Identification of Potential Perturbations Step 3: Identify Desired Ilities Step 4: Generate Function Alternatives Step 5: Generate Architecture Options Step 6: Select the "Best" Architecture Option

76 77 77 78 79 80

5.15

Problems

123

References

125

6

Transmit/Receive Modules

133

6.1

Introduction

133

4.7

Conclusions

81

6.2

Technical Challenges Often Faced in T /R Module Development

133

4.8

Problems

81

References

83

Part II Detailed Development Activities

85

6.2.1 6.2.2 6.2.3 6.2.4 6.2.5

Heat Transfer Signal Integrity Integration with Other Functions Materials Compatibility Electromagnetic Coupling

134 134 135 135 136 136

Antenna Element Technology Options

87

6.3

General Description of the T /R Module

5 5.1

Introduction

87

6.3.1 6.3.2

System Location of the T /R Module T/R Block Diagram

136 137

5.2

Based Concepts of Antennas

87

6.4

T /R Module Detailed Description

138

5.3

Antenna Development Process

88

5.4

Conventional Dipole

89

Planar Inverted-F Antenna

91

Low Noise Amplifier Low Noise Amplifier Protection High-Power Amplifier and Driver Amplifier Phase Shifter Duplexer

138 143 145 148 148

5.5

6.4.1 6.4.2 6.4.3 6.4.4 6.4.5

150

Meander Line Antenna

99

6.5

T /R Module Manufacturing and Test

5.6 5.7

Microstrip Patch Antennas

102

5.8

Bowrie Dipole Antenna

105

6.5.1 6.5.2 6.5.3 6.5.4

Integrated Circuit Manufacturing Package Manufacturing Interconnects Types T /R Module Test

150 152 153 154

5.9

Waveguide Radiators

108

6.6

Examples of T /R Modules

154

xii

Contents

Systems Engineering of Phased Arrays

6.6.1 6.6.2 6.6.3

A 3-D Ceramic T /R Module for Space-Based Applications 154 T/R Module Using Laminate Circuit Board Technology 155 60-GHz CMOS T/R Module Integrated with Antennas 155

6.7

Conclusions

6.8

Problems

156

References

156

Thermal Design, Heat Transfer Trade Studies, and Reliabili!):

159

Introduction

159

7

7.1

155

xiii

8.4

Basic Digital Beamforming

186

8.5

Adaptive Beamforming

188

8.6

Errors in Beamforming and Their Effects

190

8.7

Multiple Access Methods for 5G Phased Arrays

192

8.7.1 8.7.2 8.7.3

Orthogonal Frequency Division Multiple Access Code Division Multiple Access Other Access Technologies

192 193 193

8.8

Conclusions

194

8.9

Problems

194

References

195

Heat Transfer Fundamentals at the Integrated Circuit Level

160

9

Digital Receiver Exciters

197

7.3

Reliability and MTTF

166

9.1

Introduction

197

7.4

Example: Millimeter-Wave SATCOM Front End

168

9.2

Digital Receiver Architecture Options

199

7.5

Array Cooling Methods

171

9.3

Example Trade Study on Digital Receiver Architecture

200

7.5.1 7.5.2 7.5.3

The Challenge of Phased Array Cooling Brick Array Cooling Tile Array Cooling

171 172 175

9.4

Digital Exciter Architecture Options

204

9.5

Main Components of a Digital Receiver Exciter

204

7.6

Other Reliability Drivers for Phased Arrays

176

7.7

Materials Used for Thermal Management

177

7.8

Conclusions

177

7.9

Problems

178

9.5.1 9.5.2 9.5.3 9.5.4 9.5.5 9.5.6

Low Noise Amplifier Digital Attenuator Frequency Mixer Preselection, Image Rejection, and Antialiasing Filters Frequency Multipliers ADC

205 205 206 207 209 212

References

179

9.6

Analysis of DRXs

213

8

Analog versus Digital Beamforming

181

9.7

Conclusions

213

8.1

Introduction

181

9.8

Problems

214

References

215

8.2

Benefits and Challenges in Analog Bearnforming

182

8.3

Benefits and Challenges in Digital Beamforming

183

7.2

xiv

Contents

Systems Engineering of Phased Arrays

xv

11.5

Typical Risks in Phased Array Development

269

11.6

Advanced Development Impacts All Levels of the System

271

11.7

Other Risk Analysis Topics

272

11.8

Conclusions

272

11.9

Problems

273

225

References

274

Stripmap Synthetic Aperture Radar

232

Conclusions

275

10.5

Radar Detection Performance

240

About the Authors

279

10.6

Conclusions

244

Index

281

Part Ill System Modeling and Advanced Development Activities

217

10

Phased Arra~ S~stem Modeling

219

10.1

Introduction

219

10.2

LFOV Receiver Array

220

10.3

Multichannel Communication System Design

10.4

10.7

Problems

245

References

245

Appendix 1OA Excel Spreadsheet for the LFOV Array

246

Appendix l0B Scilab Code for the Communication System Receiver Array

248

Appendix 10C Scilab Code for the Stripmap SAR Simulation

254

Appendix lOD Gaussian ROC Curve Derivation

257

11

Advanced Development Activities for Phased Arra~s

263

11.1

Introduction

263

11.2

System Risk Management

265

11.3

Advanced Development Activities

267

11.4

Types of Advanced Development Risk Reduction Activities

268

Preface Phased arrays have traditionally been used for radar systems. However, this has changed in recent years. They are now being used or proposed for use in Internet of Things (loT) networks, high-speed backhaul communication, terabitper-second satellite systems, fifth generation (5G) mobile networks, and mobile phones. As a result, there is renewed interest and investment occurring in the development of phased array components and systems. While there are existing books on phased arrays, they are focused on radar applications (only on the antennas) and/or do not consider system design issues for phased arrays. This book fills this gap by considering systems engineering of phased arrays and addresses not only radar, but also backhaul communication systems, SG, medical, and other applications. The main premise of the book is that a systemlevel perspective and approach are essential for the successful development of modern phased arrays. This book has three main sections. Part I is Chapters 1 to 4, which give top-level systems engineering activities such as the systems engineering process, architectures, operational environments, and concept development. Part II is Chapters 5 to 9, which provides information on the detailed development of phased arrays including antennas, transmit/receive (T/R) modules, thermal design, analog versus digital beamforming, and digital receivers. Part III is on system modeling, covered in Chapter 10, and advanced development activities, covered in Chapter 11. The book concludes with Chapter 12, which is a brief summary. Chapter 1 introduces the two important concepts of this book-phased arrays and systems engineering. It describes the basic concept of a phased array with a simple example. The systems engineering process is developed with application to phased arrays. The full-system life cycle is described from concept lr'l/11

xviii

Systems Engineering of Phased Arrays

developed, detailed development, deployment and sustainment, and eventual system decommissioning. Chapter 2 describes phased array architecture alternatives. The mechanical and electrical features of phased arrays are described. Several architectures are described, including the tile array, brick array, panel array, and integrated circuit array level. This chapter also introduces topics (covered in more detail in later chapters) including antennas, analog beamforming, digital beamforming, transmit/receive modules, and integrated circuit technology for phased arrays. Chapter 3 explains several use cases for phased arrays. The first is highaltitude platform stations (HAPS) systems, medical systems with emphasis on breast cancer sensors, military radar, and 5G multiple input multiple output (MIMO). The goal of this chapter is to provide the reader with examples of how phased arrays are used in various applications. Chapter 4 gives details on how a phased array concept is developed for a particular application. The systems engineering concept development process is described and then applied to phased arrays. The approach taken in this chapter is to use "ilities" to capture user and stakeholder nonfunctional requirements. The ilities are used to drive the concept development of a phased array system. Chapter 5 describes antenna technology typically used in phased arrays. Ten different antennas are considered and design processes for them are given for each. These 10 antennas include types that are currently used in phased array, types that are commercially and economical available, and types that are considered state of the art. Examples are given for several of the antennas showing how the design processes are conducted. To facilitate system-level trade study, the main features, benefits, and drawbacks are given for each antenna type. Chapter 6 explains transmit receive modules. The block diagram of a transmit/receive (T/R) module is given and examples are shown. Several of the technical challenges are described that are often faced when developing T /R modules. A detailed description of T/R modules is given that includes component descriptions and modeling equations. Next, semiconductor materials for T/R module integrated circuits (ICs) are presented to aid the systems engineer in choosing technology solutions. The chapter concludes with examples of three-dimensional (3-D) ceramic T/R modules for space-based applications, laminate-based circuit board T/R modules, and 60-GHz CMOS (complementary metal-oxide semiconductor) T/R modules. Chapter 7 gives details on the thermal design of phased arrays. One of the system architecting challenges for phased arrays is solving the heat transfer required to remove thermal energy generated in the T /R module. This is because the heat flux generated at the active components can be several thousand watts per square centimeter. Semiconductor reliability is described, as well as packagino m-:irPri-:il r,nrir,nc -:,nrl rr,r,Jinn mPrhr,rlc

Preface

xix

Chapter 8 presents a comparison between analog and digital beamforming. The emphasis is on the realization of phased arrays using digital beamforming. In the digital beamforming approach, each element in the array is digitized, which means multiple simultaneous beams can be created. Chapter 9 describes how digital receivers can be used in phased arrays. The alternative uses digital receivers at the subarray, which allows for multiple simultaneous receive beams but without the data bandwidth handling requirements of a fully digital beamformed array. The architecture is described and examples are given. Chapter 10 shows how phased arrays can be modeled at the system level for both conventional and digital beamformings. This chapter provides the know-how for system modeling of phased arrays for communication systems and synthetic aperture radar. The foundation of every system simulation is the models used for elements of the system. Chapter 11 presents a few of the advanced development activities that occur in phased arrays. It describes system risk management, advanced development activities and how they reduce risk, typical risks in phased arrays, and the impact of advanced development on all the levels of the system. The benefits of advanced development activities are provided along with a description of the Plan B and Reverse Plan B approach. Chapter 12 is the conclusion and a short summary of the book. In the end, the reader will be provided with knowledge that can be applied in the systems engineering of phased arrays.

Acknowledgments We would like to thank the publisher for their interest in the work and support during the development process. We would also like to thank our wives and family for being patient and understanding during those times of writing and reviewing. Finally, we would like to thank the engineers and scientists with whom we have worked throughout our careers since much of what we know was learned from them.

)()(j

Part I System Engineering Activities This section of the book provides the reader with knowledge of the top-level systems engineering activities applied to phased arrays. This includes system engmeenng processes, architectures, operational environments, and concept development.

1 The Systems Engineering Process and Its Application to Phased Arrays

1.1

Introduction

Traditionally, phased arrays have been used for military radar systems. Typical applications have included airborne radar for fighter planes, ground-based radar for detection or airborne targets, and satellite-based phased arrays for communication links. Consider, for instance, the AN /TPY-2 radar in Figure 1.1, which shows the array mounted on a transportable base. It is used to detect ballistic missiles. Until recently, the majority of phased arrays have been for military systems. However, this has changed in recent years. Phased arrays are now being used or are proposed for use in the IoT networks, high-speed backhaul communication, terabit-per-second satellite systems, 5G mobile networks, and mobile phones. As a result, there is renewed interest and investment occurring in the development of phased array components and systems. The goal of this chapter is to describe the systems engineering process in the context of phased arrays. Systems engineering is described and contrasted with other engineering activities. Systems engineering emphasizes the performance of the whole system, stakeholder needs, and the complete system life cycle. Other fields of engineering may emphasis design activity, reliability, components, testing, or requirements. The systems engineer must be concerned with all these factors. As will be seen in this chapter, a major concern for systems

4

Systems Engineering of Phased Arrays

Figure 1.1 The AN/TPY-2 radar is used by for detection of ballistic missiles at ranges of 1,000 km. (Source: Public domain.)

engineering is the value delivery to users and other stakeholders through the complete life cycle of the system. It is helpful to think of the system life cycle in the three steps or phases. The first step is concept development. During this phase, stakeholder needs are analyzed and existing systems are examined to determine if they c~ ~et /he need or why they cannot. N~ctional re~irements, also called/"ili1ies," are used to capture stakeholder needs and to generllesystem ardiitecture alternatives. The alternatives are then subjected to trade study and a baseline solution is chosen. In addition, a life-cycle plan for the system is generated. Advanced development activities may also be initiated as part of the first step for the purpose of reducing program risk and to aid baseline solution selection. The second step is the actual detailed development of the baseline system. Engineering design and prototype development occur in this step. Fabrication processes, manufacturing solutions, and deployment plans are developed. At the end of the second phase, a viable solution is developed and readied for production. The third step is the production, deployment, operation, and maintenance of the system. It also includes the eventual decommissioning of the system. The systems engirfeering process is described in this chapter with application to phased arrays.

1.2

Methodological Reductionism

Before describing the systems engineering process, it is helpful to describe systems engineering itself and compare it to other engineering disciplines. Systems

The Systems Engi,neering Process and Its Application to Phased Arrays

5

engineering is a different approach compared to many other engineering activities since it is primarily concerned with the whole rather than the parts. Systems engineering is concerned with the big picture and system-level performance. Many other engineering disciplines are concerned with understanding the details and parts of systems. For instance, in a phased array, the systems engineering is concerned with the complete system, its context, customer use cases, stakeholders, value delivery over the lifetime of the system, reliability, and system performance. Compare this with the engineer ·designing the antennas used in the phased array who is concerned with its performance and its interfaces. The component designer is laser-focused on the details. The systems engineer is focused on the big picture. Boch are important and necessary. That said, the systems engineer must also be involved with the subsystems and often the components of the system. The involvement is often at the level of specifications, risk, technology maturity level, prototype plans, and analysis of alternatives for subsystems and components. For instance, the systems engineer will be required to work with the receiver-exciter development engineers. This may include the analysis of digital receivers and exciters, analog versions, che number of them per system or subarray, and the choice of supplier. The systems engineer is focused on the big picture, but muse also have the ability co analyze details at the subsystem or component level. Another way to compare systems engineering with ocher fields of engineering is to chink of the familiar process of methodological reductionism, which is the dominant method of scientific investigation. It assumes chat everything can be disassembled co its constituent parts. The goal is to understand the functioning of the parts so the complete system can be understood. It is illustrated in Figure 1.2 and a good explanation of this process is provided by Blanchard and Fabrycky [l]: Analysis consists, first, of taking apart what is to be explained, disassembling it, if possible, down to the independent and indivisible parts of which it is composed; second, of explaining the behavior of those parts; and, finally, of aggregating these partial explanations into an explanation of the whole. The process of disassembly is continued until the required level of detail is achieved or the limits of disassembly are reached. Some engineers spend a good portion of their effort on understanding the parts and developing models chat will predict their operation in the range of interest to systems. Take, for instance, the study of a T/R module used in a phased array. The module is reduced to its components such as the amplifiers, phase shifters, and control circuits. Each of the components is further reduced co their parts. For instance, the high-power amplifier in the T/R module may be reduced to its transmission lines, passive components, and transistors. Another layer of

6

Systems Engineering of Phased Arrays

The Systems Engineering Process and Its Application to Phased Arrays

7

Physical system

Decomposition into smaller parts

Predict system operation using models of the parts

System

(bl

Lower level parts are subjected study Figure 1.2 The process of methodological reductionism reduces a system to its parts for study and builds a model of the system for the purpose of predicting its behavior.

reduction may be to analyze the transistors to develop models of them. After this process of reduction and the completion of modeling, the T/R module is reconstructed in a computer model and its performance is predicted. The process of disassembly, study, and reassembly is the standard process used in most fields of study. An underlying assumption of this approach is that all observed phenomena can be explained using only mechanical cause and effect. Every observed event was the cause of some prior event and the cause. The operation of everything is considered to be like the operation of a machine. While systems engineering affirms the usefulness of methodological reductionism, it also asserts that reductionism is not the complete story or the only way to implement systems.

1.3 The Systems Engineering Approach

r

11 1...

' ',

The systems engineering approach focuses on the whole rather than the parts. Its emphasis is upon system outcomes rather than perfection of details. As Blanchard and Fabrycky described it: "It does not deny that they [systems] have parts, but it focuses on the whole of which they are part. It provides another way of viewing things, a way that is different from, but compatible with, reductionism." Systems are purposeful and developed with ends in mind particular to stakeholder a1'd user needs. In this sense, all engineered systems are understood ""''co be _!.eleological. That is, they are goal-seeking to purposeful ends for human beings or other objectives. Therefore, the systems engineer works to maximize 1 ~alue delivery to the desired objectives over the entire life cycle of the system. Although defining systems engineering can be difficult, it is possible to use three different descriptors [2] as illustrated in Figure 1.3. The first is the top-down approach. It is concerned with the system as a whole rather than just

"1 ('-.., rr

Parts

(a)

Financial

Management (c)

Figure 1.3 Illustration of systems engineering showing: (a) the top-down approach, (b) the life-cycle approach, and (c) the interdisciplinary approach.

the parts. The second is the life-cycle orientation. Rather than concern for just one aspect of the system, it is concerned with all phases from concept development to decommissioning. The third is interdisciplinary. Systems engineering requires a broad range of knowledge and expertise. These three descriptors provide some definition to systems engineering. Since the interdisciplinary nature of systems engineering is so important, it is further developed using three characteristics. First, it requires a broad range of expertise. This means that the systems engineer is expected to have a broad range of knowledge and to be a subject matter expert in at least one discipline. Second, it means that required knowledge is provided by a team of experts. When a team of experts is used, the systems engineer must work to manage the team and to extract value from it. Third, it means that the systems engineering activity requires a balance between often competing interests to transform customer needs into a system that can deliver value to the stakeholders. These are a few of the implications of the interdisciplinary nature of systems engineering.

1.4 The Three-Phase Process There are several ways to model the systems engineering process. One is the three-phase process model. The three-phase process for systems engineering is illustrated in Figure 1.4. It divides the process into concept development, engi-

8

The Systems Engineering Process and Its Application to Phased Arrays

Systems Engineering of Phased Arrays

Technology opportunities Operational deficiencies

Phase 1 Architecture and concept development Phase 2 Detailed engineering development

Baseline concept ______..,_ --,, and specifications

Phase 3 Prototype system production plan deployment plan

System production and deployment

Installed system operations and maintenance

Figure 1.4

The systems engineering three-phase process consists of concept development, engineering development, and post-development.

neering development, and post-development. Each of the phases has inputs and outputs. This allows systems engineering to be represented in a compact and easily understood model that accurately describes the process. The three phases describe systems engineering as a linear progression of steps. While the process is given as sequence of phases, it is important to recognize that the process is iterative so the whole development effort or portions of it may need to return to prior steps. For instance, a system development may move into engineering development and uncover a major system flaw. This may require a new system concept to be developed which means the development process will be required to move back into concept development. Although the three phases are shown as a linear progression, it is recognized, that in practice, the process is often iterative requiring some phases or portions of phases to be repeated.

1.5

Phase 1: Concept Development

According to this model, the first phase of the systems engineering process is concept development. During this phase, stakeholder are determined and needs are analyzed. Existing systems are examined to determine if they can meet the nPPct

:mcl whv tht>v cmnnt _ Altt>rn::itivf>s ::ir13 cJ13v13Jonf>cl rh::it h::ive the notential

9

to meet the need(s). Analysis and modeling of the alternatives are conducted to as part of the trade study of the alternatives with the goal of selecting a baseline design. The outputs from this phase are system-functional specifications and concept of the baseline solution. The inputs to this phase are operational deficiencies and technology opportunities. An operational deficiency is a statement about the existence of a gap in capabilities of existing systems and the needs of users and customers. For instance, an operational gap in a communications system may be that cosite interference between mobile phone base stations at a sporting event venue is reducing the number of callers that can be supported. Another example for a missile defense system is that existing radars can are not able to detect target threats at altitudes greater than 1,000 km and yet ballistic missile threat targets may exist with maximum altitudes of 2,000 km. Operational deficiencies are one motivation for investigating the possibility of a new system. The other input to the concept development phase is technology opportunities. A technology opportunity is something new such as a process, part, component, subsystem, or system that enables new capability. An example may be that a new semiconductor device process such as gallium nitride is now available that allows radar systems to transmit 5 or 10 times more signal power, which increases the range over which the system can detect targets. New technology opportunities are one motivation for developing a new system. The concept development stage has defined objectives. The objectives work to identify the scope of the activities that occur during this phase. The principal objectives of the concept development phase are [3]: 1. Needs analysis: Establish that there is a valid need (and market) for the new system that is technically and economically feasible. 2. Alternatives exploration: Explore potential system concepts, formulate a set of top-level system performance requirements, and validate them. Alterative systems concepts are developed and analyzed. Concepts of operation and system capabilities are generated for each of the alternatives. 3. Trade study and baseline selection: Select the most attractive system concept, define its functional characteristics, and develop a detailed plan for the subsequent stages of the engineering, production, and operational deployment of the system. The baseline system concept balances capabilities, life-cycle concerns, and cost. 4. New technology validation: Validate at the system level any new technology called for by the selected system concept and show its capability to meet requirements.

5. Risk management plan: Identify possible project risks, analyze the likelihood of the risk occurring, determine the risk impact to the system, choose which risks to actively manage, and develop a risk management plan. 6. Life-cycle plan: Develop a life-cycle plan chat captures the scope of the system from the start of the project to eventual decommissioning and disposal. The life-cycle plan will be complete, but will not contain all the detail that will be incorporated in it through the rest of the systems engineering process. For instance, it may include the fact that a new test facility is required, but at this point the life-cycle plan will only contain a list of a few of the major pieces of test equipment that are known to be required. The six objectives for the concept development phase are shown in Figure 1.5. Note that a major effort in the concept development phase occurs in needs analysis, concept exploration, and trade study/baseline selection. This is because alternatives will need to be explored through modeling, simulation, and possibly testing of key components or subsystems. The level of effort required to understand the alternatives can be significant depending upon the type of alternatives, prior work on similar systems, the level of fidelity required in the analysis, and available data. 1.5.1

The Systems Engineering Process and Its Application to Phased Arrays

Systems Engineering of Phased Arrays

10

Needs Analysis

The primary objective of the needs analysis step is to determine that there is a valid need for the system. This requires the systems engineer to determine the stakeholders who have an interest in the system. The customers, who are one type of stakeholder, must also be clearly identified. The customers of the system may not be the users of the system. Therefore, the users of the system must also be identified. As an example, consider that the customer who buys a phased ar-

ray for a 5G mobile phone base station system may be a large communications company, but the user of the system is the individual downloading content or making phone calls. The needs of the stakeholders must be understood as a part of needs analysis. An activity during the needs analysis is a realistic examination of existing systems to determine if they can be easily modified to meet the need. It may be that functionality can be added to existing systems with a software upgrade. It may be possible to form a system of systems to meet the need. For example, for detection of drones at airports, it may be possible to use existing phased array radars and systems as described in [4]. Obviously, if an existing system can meet the need, even if it requires minor modification, then why is a new system required? If the answer is that existing systems cannot meet the need, or if the cost of modifying existing systems is prohibitive, or if there are other reasons it cannot be used, then the reasons must be documented. Otherwise, the result of the needs analysis may be that a method is developed to use an existing system to meet the need. The needs analysis phase also starts the exploration of nonfunctional system properties. One method for converting customer needs into system nonfunctional requirements is based on the use of "ilicies'~ Examples of iiities are reliability, manufacturability, maintainability, ~testability. Ilities are ~ o ~ a l ~equirem~nts chat capture user and customer needs. They are defined as [5]: "desired properties of systems, such as flexibility or maintainability, that o~e~~a.:_nifest them!e~er after? system has been put to its initial u.:S These properties are not the primary functional requirements of a system's performance, but typically concern wider system impacts with respect to time and stakeholders than are embodied in chose primary functional requirements." Needs can be captured in the language of iii ties and used later in the trade study and baseline selection step to choose between alternatives. This is accomplished by using ilities as part of the selection criteria in the selection matrix. 1.5.2

Concept Development • Needs Analysis • Alternatives Exploration • Technology Validation • Trade Study Baseline Selection • Proactive Risk Management • Advanced Development Activities Figure 1.5 The concept development phase includes needs analysis, concept exploration, trad_e s~udy/baseline selection, new technology validation, risk management plan, and life-

11

Alternatives Exploration

]/

This step determines two main items. T h e ~ system concepts chat have the potential to meet customer needs. One method is to use ideation sessions with subject matter experts. The process of developing new systems to meet user expectations is a creative process that has been the subject of intense study [6-8]. It is described as [9]: "a matter of generating, developing and communi- , eating ideas, where 'idea' is understooaasaoas1c element of thought that can be either visual, concrete or abstract." One approach to ideation is that it is a rather loosely structured session or completely unscheduled, but is essentially ad hoc with open creativity. Another approach to ideation is the TRIZ method [10, 11]. TRIZ is the Russian acronym for the English translation "Theory of

12

Systems Engineering of Phased Arrays

Inventive Problem Solving" and was developed by G. S. Altshuller in the former U.S.S.R. It uses patterns of problems and solutions instead of ad hoc methods. In addition, it has shown that TRIZ can also be used as a framework for trade studies in [12] . These ideation sessions can generate system architecture options. If predecessor systems exist, additional techniques can be used to develop system alternatives. If the system configuration allows it, then an analysis can be conducted to determine the parts of the system which contribute the most to the gap between the system performance and user needs. A systematic approach to apply is given in [13]: 1. Partition the system into its major subsystems. 2. Postulate alternatives that replace one or more of the subsystems essential to the mission with an advanced, less costly, or otherwise supe. . nor version. 3. Vary the chosen subsystem (or superior version) singly or in combination. 4. Consider modified architectures, if appropriate. 5. Continue until you have a total of four to six meaningful alternatives. /

/ The second main item determined during this step is a set of system perormance requirem~ts-that often occurs during alternatives development. One method is to use requirement elicitation. This is the use of various techniques to obtain requirements from stakeholders and other sources [14]. It is also the activity of refining requirements. It may be tempting to jump directly into defining only functional requirements of the system early in the concept development phase. However, it is best to avoid this approach for phased arrays (and most any system) during the early part of concept development since it may limit the types of systems that will be considered during the alternatives' exploration phase. As noted by Carpino and Nichele [15], "prematurely translating the perceived stakeholders needs into design requirements, is often a consequence of insufficient regard to the end-users priorities." Instead, include nonfunctional system properties and life-cycle properties (such as ilities) as part of the requirement space that is later used in baseline selection. The requirements that are developed may include functional requirements, quality requirements, and constraints on the system. Two other methods for capturing requirements are the system context and concepts of operation. The context is a statement and diagram that describe the boundaries of the system and its environment. The environment may include other systems, users, weather, operators, and government regulators. The

The Systems Engineering Process and Its Application to Phased Arrays

13

system context diagram usually includes the system inputs and outputs. This information can be useful in developing requirements. Concepts of operation (CONOPS) are statements and diagrams that describe how the system will be used. They often include statements and illustrations of the objectives or end states the system can achieve. Using system context and concepts of operation are methods to capture system needs. As a short example of a concept of operations, consider the graphic shown in Figure 1.6. It illustrates a fighter aircraft that is enabled with an active electronically steered array (AESA), which is a type of phased array found on modern aircraft platforms. It provides a graphical description of the mission scenario. It shows the main operational concepts and the unique characteristics. The figure is a simple example of an operational view-I (OV-1), which is part of the U.S. Department of Defense Architecture Framework (DoDAF). An OV-1 is a useful tool for discussion and presentation of the concept of operations. It provides an executive summary. Requirements engineering is an important function and a subdiscipline in systems engineering [ 16]. Some stakeholders are eager to share their needs and system requirements. Other times, the systems engineer will have to use survey methods such as interviews with stakeholders and questionnaires. While many requirements will be obtained from stakeholders, others can be obtained from documentation of similar systems that have been developed. Another source of system requirements is the simulations performed on alternatives. As alternatives are developed and examined during trade studies, it is possible to obtain system requirements from simulations. This is because the simulations may demonstrate capabilities that can be converted into requirements. System requirements can be obtained using several methods.

I t

•

•

0

•

f

•

-

AESA Enabled Fighte~

•

I•

l

•

Search ~

~

,

•

•

•

k

Example OV-1 illustrating a fighter aircraft enabled with an AESA that simultaneously provides communication, weapons delivery, search and track, and ground moving target indicator (GMTI) functions. Figure 1.6

14

Systems Engineering of Phased Arrays

The Systems Engineering Process and Its Application to Phased Arrays

15

Two outputs from this step are top-level system performance requuements and a set of 4 to 6 system alternatives. "O

1.5.3 Trade Studies and Baseline Selection

The baseline system is selected by performing a trade study, which ranks the alternatives against weighted system needs. An important part of this activity is performing system-level modeling, which provides the data that populates part of the trade study matrix. A methodology in systems engineering is modelbased engineering (MBE). It uses models (often graphical models) to represent the elements of a system. The engineer can then model the performance of the system against user needs and/or ilities to provide data used in trade studies. For phased arrays, the system model can be constructed using multiple methods. The simplest to use may be spreadsheets. Some phased array engineers have developed sophisticated array models in spreadsheets that allow for nearly instantaneous trade study results and what-if simulations. For instance, it is very common for phase array engineers to use spreadsheets to perform link budget calculations for communication systems and for signal-to-noise ratio analysis radar systems. Another option is to use commercially available numerical computing software. Some vendors of numerical computing software have phased array tools that can be added as options. Phased array system designers use numerical computing software to analyze options and provide information for use in trade studies. Others write their own custom software programs. Some organizations have developed high-fidelity phased array analysis software that can allow for rapid analysis of array options. For instance, some organizations have custom software to predict array patterns (with coupling between elements), array scan performance (showing grating lobes), array current distribution, and estimate antenna gain. However, another option is to use commercially available visual system simulators for phased array modeling [17]. Some of the simulators have phased array elements included as a standard modeling element. There are multiple options available to the systems engineer for modeling phased arrays to generate some of the data used in the trade study. A process for using ilities as a method for selecting a baselines system is given in [15]. The method uses a quality function deployment (QFD) matrix and rates the ability of each system alternative to meet ilities. The ilities in the matrix are ranked and weighted by importance. The system alternative that best meets the ilities is chosen as the baseline solution. This approach was extended in [18] to include the selection of subsystems and even components. A simplified trade study matrix for selecting the baseline solution is shown in Figure 1.7. As part of the trade study analysis, several selection criteria are used. They are generated throughout the concept development phase and should include nonfunctional orooerties of the systems described using ilities as

"O

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-"'

c..

,

~ - 40

O' - - - -

Figure 3.3 Breast cancer imaging system showing an array of 16 antenna elements in a hemispherical shape. (© 2009 IEEE. Reprinted, with permission, from [20].)

63

Edge Average Throughput type (a)

0

I

100

■

200

■

300

Number of users

(bl

Figure 3.4 Comparison of the benefit of using SOMA compared to TOMA for based on user data throughput for (a) edge users and the average user in a distribution of 100 users, and (b) the average user throughput as a function of the number of users. (© 2017 IEEE. Reprinted, with permission, from [28].)

64

Use Cases for Phased Arrays

Systems Engineering of Phased Arrays

SDMA. The SDMA system used a framework consisting of a joint scheduling and resource allocation algorithm. It improves resource utilization efficiency and yet has low complexity with reduced required computational resources. As can be seen from the figure, data rates increase from 50 to 70 Mbps to over 300 Mbps. The digital beamforming system uses one or more access points with an array of antenna elements that use adaptive beamforming to optimize system performance. The benefits of this arrangement for 5G systems are basically the same as for other phased array systems and they are: 1. Increased user throughput: The user experience is improved because the data rate is increased. 2. jamming immunity: Using adaptive beamforming, an antenna null can be placed in the direction of the jamming signal. Using this method, it is possible to place antenna nulls that will reduce the signal level of the jammer by as much as 20-30 dB compared to the desired signal. 3. Reduced interference: Because of adaptive beamforming, it is possible to minimize the effect of interfering cosite signals from other base stations, user equipment, or other backhaul systems. This is also achieved using adaptive beamforming to place nulls in the direction of the interfering signal. 4. Reduced power consumption for user equipment: Applications in which access points or base stations are using beamforming provide antenna gain in the direction of the user equipment. In applications in which battery power is a primary concern such as internet-of-things devices, the transmit power from the user equipment can be reduced and maintain the same data rate.

65

tenna beams. The system operates in a 15-GHz band. Their results showed an increase of 125% in data throughput.

3.5

Airborne Radar for Fighter Aircraft

The highest-end phased arrays are used in military applications. They provide advanced capabilities in the hardware and in software algorithms. There are many different examples including ground-based systems such as AN/TPY-2 radar used in THAAD missile defense system and airborne radars such as the AN/APG-81 used on the Joint Strike Fighter F-35. These highly capable and multifunction radars used phased arrays as the key enabling technology. 3.5.1

Introduction to Military Phased Arrays

Phased arrays for military applications have been enabled by several technology advancements over the past few decades [32]. Many of them have been due to industrial investments in research and development but most have been due to government sponsored developments. A few of the advancements are: • Gallium arsenide, silicon geranium, and gallium nitride monolithic microwave integrated circuit (MMICs); • Digital beamforming; • Digital signal processing; • Space-time adaptive processing (STAP); • Electronic packaging and assembly; • Software used to design phased arrays (i.e., 3-D electromagnetic simulators).

These are a few of the benefits of adaptive beamforming for 5G systems. 3.4.3

5G Phased Array Examples and Summary

There are several examples of proposed and deployed 5G systems using MIMO beamforming. One example is a proof of concept system using massive MIMO beamforming at 2.4 GHz described in [29]. The system used various combinations of 8, 16, and 32 active elements in an array of patch antennas along with software-defined radios. As expected, the results show an increase in data rate as the number of active elements in the array is increased. Another example in [30, 31] described indoor and outdoor field experimental results with a base station containing a 64-element array with analog beamforming and 48 possible an-

These advancements have resulted in advanced system capabilities for phased array radars. The next section describes the key challenges and benefits of airborne radar for fighter aircraft. 3.5.2 Airborne Phased Array System Description with Key Challenges and Benefits

The most sophisticated and capable phased arrays that have been widely deployed are for airborne radar applications on fighter planes such as the F-35 Joint Strike Fighter. These radars have phased arrays with many transmit/receive (T/R) modules. These systems offer some impressive benefits compared to older radars. A few of the benefits are [33, 34]:

66

67

1. Beamsteering agility: The radars are able to steer their radar beams rapidly.

3.6

2. Multiple simultaneous modes: Arrays can support multiple modes such as search, track, moving target indication (MTI), and communication.

The field of use cases is an important pare of systems engineering and is part of the requirements analysis. The approach to use cases in this chapter may be considered by some to be a limited application of the available breath of knowledge that has been developed. For instance, the approach in [38] expands the definition of use case to be an agile practice (or set of practices) that captures a set of requirements and drives the incremental development of a system that fulfills them. The point in this approach is that the use case does more than communicate the ways that a system achieves its goals. On this definition, the use case is a tool that helps systems engineers develop an appropriate system that meets user needs-it supports the development of the system. The point is that the interested reader can expand the use cases presented in this chapter so that they can be used to help drive the development systems. This chapter provides the systems engineering with three types of systems that can benefit from functionality provided by phased arrays. The benefits and challenges of the systems have been provided and several example systems were described. This information demonstrates the wide range of systems that can use phased arrays to meet customer needs and stakeholder expectations.

3. Subarray reconfiguration according to desired operating modes: Each subarray in the array can be reconfigured to support a unique operating mode. 4. Improved mechanical reliability: Since there are no moving parts to introduce mechanical failures, the radars arrays are more reliable. 5. More reliable electrics and graceful degradation: Because amplifiers and beam-steering phase shifters are distributed on the face of the array in transmit/receive (T/R) modules, it makes the radars much more reliable since it avoids the single-point failure. As T /R modules begin to fail, radar performance degrades gracefully rather than abruptly, which can be a critical benefit when in operation. While these are important system benefits and they are all enabled because of the phased array, there are also several challenges in developing and deploying them. A few of them are: 1. Thermal dissipation and heat transfer: This is a challenge because significant heat is generated in the T /R modules and it must be removed. Most (or all) high-performance airborne radars use liquid cooling to conduct away the heat generated by the T /R modules. 2. Electronic packaging: The electrical circuit density, operating frequency (normally X-band), operational environment, and heat generated require significant effort and expense in proper electronic packaging. 3. Calibration: Sophisticated methods need to be used for array calibration such as near-field chamber (NFC) methods [35, 36]. 3.5.3

Use Cases for Phased Arrays

Systems Engineering of Phased Arrays

3.7

Problems

Q3. l

Describe a HAPS system in general terms in one paragraph. Describe an example of a phased array chat is used in a HAPS system.

Q3.2

If a HAPS system is located at an altitude of 20 km, what field of view is required for the phased array antenna to achieve a circular spot pattern on Earth with a diameter of 30 km?

Q3.3

If the altitude of the HAPS system in Q3.2 can vary by+/- 1 km, what field of view is required in the array to ensure coverage over the full 30km diameter spot pattern?

Q3.4

Perform an internet search and find an example of a breast cancer sensor using phased arrays not already given in this book. Provide the reference or web address and describe the system in a paragraph.

Q3.5

What are three challenges in using phased arrays for medical applications?

Q3.6

What are three advantages of using phased arrays at microwave frequencies for medical treatment and diagnosis?

Airborne Phased Array Examples and Summary

There are several examples, but the two discussed here are the AN/APG-79 radar (for F-18 aircraft) and theAN/APG-81 (for F-35 aircraft). TheAN/APG79 radar was developed for deployment on the F/A-18E/F Super Hornet and the EA- l 8G Growler. The radar allows for simultaneous air-to-air and air-toground modes. This means that it can deliver weapons to targets while defending itself [37].

Conclusions

68

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Alexander, I., and T. Zink, "Introduction to Systems Engineering with Use Cases," Computing & Control Engineering Journal, December 2002, pp. 289-297.

[2]

Cockburn, A., Writing Effective Use Cases, Reading, MA: Addison-Wesley, 2001.

[3]

d'Oliveira, F., F. de Melo, and T. Devezas, "High-Altitude Platforms-Present Situation and Technology Trends," Journal ofAerospace Technology and Management, Vol. 8, No. 3, July-September 2016, pp. 249-262.

[4]

Clark, T., and E. Jaska, "Million Element ISIS Array," Proceedings of2010 IEEE International Symposium on Phased Array Systems and Technology, Waltham, MA, October 12-15, 2010.

[5]

Sturdivant, R., and J. Lee, "Systems Engineering of IoT Connected Commercial Airliners Using Satellite Backhaul Links," Proceedings of2018 IEEE Topical Workshop on Internet of Space (TWIGS), Anaheim, CA, January 14-17, 2018.

[6]

Alsarnhi, S., I. Yemen, and N. Rajput, ''An Intelligent HAP for Broadband Wireless Communications: Developments, QoS, and Applications," International Journal ofElectronics and Electrical Engineering, Vol. 3, No. 2, April 2015, pp. 134-143.

[7]

Sturdivant, R., and E. Chong, "System Latency Performance of Mechanical and Electronic Scanned Antennas for LEO Ground Stations for Io T and Internet Access," Proceedings of IEEE 2011 Topical Workshop on Internet of Space (TWIGS), Phoenix, AZ, January 15-18, 2017.

[8]

Huang, J., Y. Liou, and H. Ferng, "The Effect of Platform Displacement on a HAPS CDMA System with Multibeam Antennas," Proceedings of2008 IEEE 19th International Symposium on Personal, Indoor, and Mobile Radio Communications, Cannes, France, September 15-18, 2008.

[9]

Huang, J., et al., "The Impact of Using Multiple HAPS to Combat Platform Instability on Uplink CDMA Capacity," Proceedings of2007 IEEE 65th Vehicular Technology Conference (VTC2007-Spring), Dublin, Ireland, April 22-25, 2007.

[IO]

Kang, B., B. Ku, and D. Ahn, "Ka Band Active Phased Array Antenna with Digital Beam Forming for the HAPS Systems," Proceedings of IEEE 2003 International Symposium on Personal, Indoor, and Mobile Radio Communications, Beijing, China, September 7-10, 2003.

[11 ]

Huang,]., Z. Wu , and W Wang, "Designs ofMicrocell for an Integrated HAPS-Terrestrial CDMA System," Proceedings of 2008 IEEE 19th International Symposium on Personal, Indoor, and Mobile Radio Communications, Cannes, France, September 15-18, 2008.

[12]

Widiawan, A., and R. Tafazolli, ''Analytical Investigation on Sharing Band Overlaid High Altitude Platform Station-Terrestrial CDMA System," Electronic Letters, Vol. 41, No. 2, February 2005, pp. 77-79.

[13]

Use Cases for Phased Arrays

Systems Engineering of Phased Arrays

Teunissen, W , V. Jain, and G. Menon, "Development of a Receive Phased Array Antenna for High Altitude Platform Stations Using Integrated Beamformer Modules," Proceedings ofIEEE International Microwave Symposium, Penn, PA, June I 0-15 , 2018.

69

[I 4]

Kowalski, M., et al., "Optimization of Electromagnetic Phased-Arrays for Hyperthermia Via Magnetic Resonance Temperature Estimation," IEEE Trans. on Biomedical Engineering, Vol. 49, No. 11, November 2002, pp. 1229-1241.

[15]

Chandra, R., et al., "On the Opportunities and Challenges in Microwave Medical Sensing and Imaging," IEEE Trans. on Biomedical Engineering, Vol. 62, No. 7, July 2015, pp. 1667-1682.

(16]

Gagarin, R., et al., "Determination of Pulmonary Edema Using Microwave Sensor Array: Simulation Studies with Anatomically Realistic Human CAD-Models," Proceedings of 2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), Orlando, FL, July 7-13, 2013.

[17]

Latif, S., D. Nelson, and V. La, ''An On-Body Conformal Printed Array Antenna at Mmwave Frequencies for Healthcare Applications," Proceedings of2016 17th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM), Montreal, Canada, July 10-13, 2016.

[18]

Xie, Y., et al., "Mulcistatic Adaptive Microwave Imaging for Early Breast Cancer Detection," IEEE Trans. on Biomedical Engineering, Vol. 53, No. 8, August 2006, pp. 1647-1657.

[19]

Bucci, 0., et al., "On the Design of Phased Arrays for Medical Applications," Proceedings ofthe IEEE, Vol. 104, No. 3, March 2016, pp. 633--648.

[20]

Klemm, M., et al., "Radar-Based Breast Cancer Detection Using a Hemispherical Antenna Array-Experimental Results," IEEE Trans. on Antennas and Propagation, Vol. 57, No. 6, June 2009, pp. 1692-1704.

[21]

Klemm, M., et al. , "Experimental and Clinical Results of Breast Cancer Detection Using UWB Microwave Radar, " Proceedings of IEEE Antennas and Propagation Society International Symposium, San Diego, CA, July 7-12, 2008.

[22]

O'Loughlin, D., "Microwave Breast Cancer Imaging: Clinical Advances and Remaining Challenges," IEEE Trans. on Biomedical Engineering, Early Access, February 27, 2018.

[23]

Sun, S., et al., "MIMO for Millimeter-Wave Wireless Communications: Beamforming, Spatial Multiplexing, or Both?" IEEE Communications Magazine, December 20 I 4, pp. 110-121.

[24]

Pi, Z., and F. Kahn, ''An Introduction to Millimeter-Wave Mobile Broadband Systems," IEEE Communications Magazine, Vol. 49, No. 6, June 2011, pp. 101-107.

[25]

Li, Q., and G. Li, "MIMO Techniques in WiMAX and LTE: A Feature Overview," IEEE Communications Magazine, Vol. 48, No. 5, May 2010, pp. 86-91.

[26]

Ertel, R. , "Overview of Spatial Channel Models for Antenna Array Communication Systems," IEEE Personal Communications, Vol. 5, No. 1, February 1998, pp. 10-22.

[27]

"View on 5G Architectures (Version 2.0)," 5G Public Private Partnership (PPP) Architecture Working Group, July 18, 20 I 7.

[28]

Li, Y., et al., "Radio Resource Management Considerations for 5G Millimeter-Wave Backhaul and Access Networks," IEEE Communications Magazine, Vol. 55, No. 6, June 2017, pp. 86-92.

68

References [l]

Alexander, I., and T. Zink, "Introduction co Systems Engineering with Use Cases," UJ puting & Control Engineering journal, December 2002, pp. 289-297.

[2]

Cockburn, A., Writing Effective Use Cases, Reading, MA: Addison-Wesley, 2001.

[3]

d'Oliveira, F., F. de Melo, and T. Devezas, "High-Altitude Platforms-Present Sicuaw and Technology Trends," journal ofAerospace Technology and Management, Vol. 8, o. July-September 2016, pp. 249-262.

[4]

Clark, T., and E. Jaska, "Million Element ISIS Array," Proceedings of2010 IEEE Interr. tional Symposium on Phased Array Systems and Technology, Waltham, MA, October 12-1' 2010.

[5]

Sturdivant, R., and J. Lee, "Systems Engineering of Io T Connected Commercial Airlin . Using Satellite Backhaul Links," Proceedings of2018 IEEE Topical Workshop on Intemtr Space (TWIGS), Anaheim, CA, January 14--17, 2018.

[6]

Alsamhi, S., I. Yemen, and . Rajput, ''.An Intelligent HAP for Broadband Wireless Corr munications: Developments, QoS, and Applications, " International journal of Electro11 and Electrical Engineering, Vol. 3, No. 2, April 2015, pp. 134--143.

[7]

Sturdivant, R., and E. Chong, "System Latency Performance of Mechanical and El tronic Scanned Antennas for LEO Ground Stations for loT and Internet Access," Prom ings ofIEEE 2017 Topical Workshop on Internet ofSpace (TWIGS), Phoenix, AZ, Janua 15-18, 2017.

[8]

H uang, J., Y. Liou, and H. Ferng, "The Effect of Platform Displacement on a HAP CDMA System with Mulcibeam Antennas," Proceedings of2008 IEEE 19th Intematio, Symposium on Personal, Indoor, and Mobile Radio Communications, Cannes, France, er tember 15-18, 2008.

[9]

Huang, J ., et al., "The Impact of Using Multiple HAPS co Combat Platform lnstabilityo Uplink CDMA Capaciry," Proceedings of2007 IEEE 65th Vehicular Technology Confern (VTC2007-Spring), Dublin, Ireland, April 22-25 , 2007.

[10]

Kang, B. , B. Ku, and D. Ahn, "Ka Band Active Phased Array Antenna with Digital Bea,:, Forming for the HAPS Systems," Proceedings of IEEE 2003 International Symposium Personal, Indoor, and Mobile Radio Communications, Beijing, China, September 7-ll 2003.

(11]

H uang, J., Z. Wu, and W. Wang, "Designs ofMicrocell for an Integrated HAPS-Terrestri CDMA System," Proceedings of 2008 IEEE 19th International Symposium on Pmon., Indoor, and Mobile Radio Communications, Cannes, France, September 15-18, 2008.

[12]

Widiawan, A. , and R. Tafazolli, ''.Analytical Investigation on Sharing Band Overlaid Hig Altitude Platform Station-Terrestrial CDMA System," Electronic Letters, Vol. 41, o.• February 2005, pp. 77-79.

(13]

Use Cases or Phased Arra s

Systems Engin ee rin g of Phased Arrays

Teunissen, W , V Jain, and G. Menon, "Development of a Receive Phased Array Anteon for H igh Altitude Platform Stations Using Integrated Beamformer Modules," Proceedin ofIEEE International Microwave Symposium, Penn, PA, June 10- 15, 2018 .

69

ki, M ., et al., "Optimization of Electromagnetic Phased-Arrays for Hyperthermia Magnetic Resonance Temperature Estimation, " IEEE Trans. on Biomedical Engineering,

I 49, No. 11 , November 2002, pp. 1229-1241. dra, R., et al., "On the Opportunities and Challenges in Microwave Medical mg and Imaging," IEEE Trans. on Biomedical Engineering, Vol. 62, No. 7, July 2015, 1667-1682. rin, R., et al., "Determ ination of Pulmonary Edema Using Microwave Sensor Array: ulation Studies with Anatomically Realistic Human CAD-Models," Proceedings

2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), Orlando, FL, July 7-1 3, 2013.

uf. S., D . Nelson, and V La, "An On-Body Conformal Printed Array Antenna at Mmwave Frequencies for H ealthcare Applications," Proceedings of2016 17th International iposium on Antenna Technology and Applied Electromagnetics (ANTEM), Montreal, Canada. July 10-1 3, 20 16. Y., et al., "Multistatic Adaptive Microwave Imaging for Early Breast Cancer

Det tion," IEEE Tram. on Biomedical Engineering, Vol. 53, No. 8, August 2006, pp. 1647-1657. Bucci, 0., et al. , "On the D esign of Phased Arrays for Medical Applications," Proceedings tk IEEE, Vol. 104, No. 3, March 2016, pp. 633-648. Klemm, M., et al. , "Radar-Based Breast Cancer Detection Using a Hemispherical Antenna y-Experimental Results," IEEE Trans. on Antennas and Propagation, Vol. 57, No. 6, unc 2009, pp. 1692-1704. Klemm, M., et al. , "Experimental and Clinical Results of Breast Cancer Detection mg UWB Microwave Radar," Proceedings of IEEE Antennas and Propagation Society flkrnational Symposium, San Diego, CA, July 7-12, 2008.

Loughlin, D ., "Microwave Breast Cancer Imaging: Clinical Advances and Remaining Challenges," IEEE Tram. on Biomedical Engineering, Early Access, February 27, 2018. un S., et al., "MIMO fo r Millimeter-Wave Wireless Communications: Beamforming, rial Multiplexing, or Both?" IEEE Communications Magazine, December 2014, p 110-121.

P Z., and F. Kahn, ''.An Introduction to Millimeter-Wave Mobile Broadband Systems," IEEE Communications Magazine, Vol. 49, No. 6, June 2011, pp. 101-107.

Li Q., and G. Li, "MIMO Techniques in WiMAX and LTE: A Feature Overview," IEEE Communications Magazine, Vol. 48, No. 5, May 2010, pp. 86-91.

End. R., "Overview of Spatial Channel Models for Antenna Array Communication terns," IEEE Personal Communications, Vol. 5, No. l, February 1998, pp. 10-22. View on 5G Architectures (Version 2.0), " 5G Public Private Partnership (PPP) Architecture Working Group, July 18, 2017.

Li Y., et al., "Radio Resource Management Considerations for 5G Millimeter-Wave Backhaul and Access Networks," IEEE Communications Magazine, Vol. 55, No. 6, June 201 7, pp. 86-92.

Systems Engineering of Phased Arrays

70 (29]

Wirth, T., et al., "Proof-of-Concept of Flexible Massive MIMO Beam forming at 2.4GHz," Proceedings of 2017 51st Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, October 29-November 1, 2017.

(30]

Tateishi, K., et al., "Outdoor Experiment on User Mobility Using Distributed MIMO Beamforming for 5G Radio Access," Proceedings of2018 IEEE Wireless Communications and Networking Conference (WCNC), Barcelona, Spain, April 15-18, 2018.

[31]

Kurita, 0., et al., "Indoor and Outdoor Experiments on 5G Radio Access Using Distributed MIMO and Beamforming with a Variety ofTP Deployments," Proceedings of 2017 IEEE 86th Vehicular Technology Conference (VTC-Fall), Toronto, Canada, September

4

24-27, 2018. (32]

Brookner, E., "Advances and Breakthroughs in Radar and Phased Arrays," Proceedings of 2016 CIE international Conference on Radar (RADAR), Guangzhou, China, October 10-13, 2016.

[33]

Kemkemain, S., A. Larroque, and C. Enderli, "The Industrial Challenges of Airborne AESA Radars," Proceedings of JET International Radar Conference 2013, Xi'an, China,

Phased Array Concept Development Example

April 14-16, 2013. [34]

Gautier, W., W. Gruener, and M. Kirscht, "Technology Challenges and Opportunities for Next Generation AESA Based Airborne Surveillance Radar," Proceedings ofEUSAR 2016: 11th European Conference on Synthetic Aperture Radar, Hamburg, Germany, June 6-9,

4.1

Introduction

2016. [35]

Aumann, H., and F. Willwerth, "Phased Array Calibrations Using Measured Element Patterns," Proceedings ofIEEE Antennas and Propagation Society International Symposium, Newport Beach, CA, June I 8-23, 1995.

(36]

Fulton, C., and W. C happell, "Calibration Techniques for Digital Phased Arrays," Proceedings of 2009 IEEE international Conference on Microwaves, Communications, Antennas and Electronic Systems, Tel Aviv, Israel, November 9-11, 2009.

[37]

Brookner, E., "Phased-Array Radar Astounding Breakthroughs-An Update," Proceedings of2008 IEEE Radar Conference, Rome, Icaly, May 26-30, 2008.

[38]

Jacobson, I., I. Spence, and K. Biemer, Use-Case 2.0: The Guide to Succeeding with Use Cases, London, England: IVAR Jacobson Internacional, 2011.

This chapter is concerned with how to apply systems engineering methods to develop system concepts. This chapter delivers additional details and other options to concepts developed that were presented in Chapter 1. Specifically, a detailed process for using ilities to generate a system architecture and baseline concept is given. This chapter is also different from Chapter 2 because it provides a process that can be used to convert system nonfunctional requirements into a baseline system concept with phased arrays. However, Chapter 2 describes and contrasts the main system architecture types and provides a theoretical and practical understanding of them. The emphasis of this chapter is on system concept development. When it comes to developing a new system, a primary function of the systems engineer is to translate operational needs and technology opportunities into a viable system baseline concept. There are certainly other functions that a systems engineer performs, but this is one of the tasks that distinguish it from job functions such as program management and detailed engineering. While it is true that it is not possible to develop a single process or even a suite of processes that apply in every situation, it is possible for them to be adapted to fit specific needs. The reader is encouraged to learn the method presented and to modify it to fit specific systems.

71

Phased Array Concept Development Example

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72

73

The chapter begins with a description of the two inputs to concept development, needs (operational deficiencies) and technology opportunities. Suggestions on generating system needs and on finding technology opportunities are given. The system archicecting with ilities (SAI) method is described. The chapter concludes with some suggestions on applying it. The summary wraps up the chapter.

projectiles, but is not capable of detecting and tracking drones. The gap is the difference between the desired capability, detecting drones, and the current capability, detecting artillery projectiles. Determining needs is the process of identifying and quantifying gaps. A resource for needs assessment is given in [2].

4.2

The other input to concept development is technology opportunities and it is illustrated in Figure 1.4 in Chapter 1. They are new ideas, products, materials, manufacturing processes, and integration approaches. For many industries and companies, technology opportunities are the engine of success. Moreover, it has been recognized for some time that technology innovation is required for corporate growth and for wealth creation in nations [3]. Therefore, considerable research has been devoted to analysis of how to discover technology opportunities and technology innovation. Technology opportunities are the other input to concept development. One approach to the discovery of technology opportunities within organizations is to exploit existing technology and products as described in [4]. On chat approach, organizations use a function-based framework with a structure of information on produces and technologies. One way co expand on chis framework is to use big data methods to extract information from patents and ocher sources similar to what is described in [5, 6]. A possible benefit of chis approach is a more economical method for discovery of technology opportunities. Ocher methods are available for technology opportunity discovery and a practical guide is given in [7], but the point in chis section is chat they are one of the inputs to concept development and can be critical to successful system development.

Needs Assessment-A Common Starting Point

As was described in Chapter 1 in Figure 1.4, a new system concept development starts with operational deficiencies and technology opportunities as inputs. Operational deficiencies are the needs experienced by users and other system stakeholders and they can be discovered using a needs assessment. Needs assessment can be straightforward for some systems. For instance, consider the automotive need for a system that reacts faster and more reliably than humans to possible collisions. This need is an input that was the basis for an automated cruise control and collision avoidance systems in automobiles. For other systems, the needs will be less obvious and more difficult to identify. The discovery of needs can also be a speculative endeavor. Consider the vision of the innovator Steve Jobs, cofounder of Apple, who was able to see that customers needed smart phones and other smart devices. As described in [l], entrepreneurs use their prior knowledge and information distributed in society for opportunity (needs) discovery. Regardless of the source of the needs, new system development starts with a needs assessment, which feeds into the concept development. One approach to needs assessment is to focus on what are called gaps, which are the difference between current and desired results. On this approach, the needs are the gaps illustrated in Figure 4.1. An example of a gap is that a particular fire finder radar system is excellent at detecting and tracking artillery Current results

Desired results

D

D Gap = system need

figure 4.1

Illustration of gaps between desired and current results are system needs.

4.3

Technology Opportunities

4.4 System Architecting System architecture is an important step in the development of a baseline concept. This is because it sets many important aspects of the solution and guides future development. However, what is system archiceccing? As a starting point, consider the following definitions: 1. In IEEE Std 610.12 [8], architecture is defined as "organizational structure of a system or component." 2. In the ISO/IEC/IEEE 24765 Internacional Standard [9], it is defined as "fundamental organization of a system embodied in its components, their relationships co each other, and to the environment, and

74

Phased Array Concept Development Example

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the principles guiding its design ad evolution ... the organizational structure of a system and its implementation guidelines." 3. In [10], the authors defined "architecting as the process of structuring the components of a system, their interrelationships, and their evolu. . non over nme.

User needs Technology opportunities

75

Determine value proposition & constraints Identify potential perturbations

))

The last definition includes the fact chat systems will change over rime as environments and needs evolve. As will be seen, chis is one of the motivators for the architecting method described in the next section as it has the potential to meet evolving user and stakeholder needs. With the inputs to the concept development phase explained and system architeccing described, the process of concept development using the SAi method will be given in the next section.

Identify initial desired llities Generate fu nction alternatives Generate are hite ctu re options

4.5 The SAi Method for New System Concept Development This section describes a modification to the SAI method for developing systems architecture and the resulting system baseline concept. The method was originally developed for application to system of systems and uses eight steps, but it has been modified for use in subsystems in [11] and reduced to six steps. Using the modified SAI method with its six steps is appropriate for most phased· arrays because they are usually considered a subsystem of a larger platform. For instance, a phased array radar for a military fighter aircraft is usually considered a subsystem of the avionics and larger aircraft platform. As an introduction to the modified SAI method, consider the six steps illustrated in Figure 4.2: Step 1: Determine value proposition and constraints. This step requires the identification, understanding, and documentation of overall system value propositions. Step 2: Identify potential perturbations. This is the identification and categorization of possible perturbations that can interfere with system value delivery. Step 3: Identify initial desired ilities. In chis step, the ilities are identified chat promote the long-term behavior of the system. Combining +ossible perturbations with desired ilities can begin to distinguish iii ties. Step 4: Generate function alternatives. The purpose of this step is to generate value-driven (values from Step 1) functional alternatives for the system architecture. The result is a list of options chat exist for each of the main subsystem functions.

Select "best" architecture solution figure 4.2

The six steps to the modified SAi method.

Step 5: Generate architecture alternatives. This step is concerned with the generation of and selection of options that can be added to architecture alternatives to achieve desired ilities. This is accomplished by combining the various function options from Step 4. Step 6: Select "best" architecture solution. The output from this final step is the baseline solution chat will be carried forward into detailed design. This step will include analysis of each option such as simulations, and prototype testing. This last step will use ilicies with the quality function deployment (QFD) trade study approach as described in [12].

4.6 Application of the Modified SAi Method to Broadband Access for Small to Medium-Size Public Venues A full treatment of the modified SAI method is beyond the scope of chis chapter. Therefore, only the main content of each step will be illustrated. Nevertheless, this will provide the reader with enough information to apply the technique. However, before the six steps can begin, operational deficiencies (needs and needs analysis) and technology opportunities need to be described. For

76

the illustration in this chapter, we will consider only one user need. In practice, there are often many user needs that systems and subsystems must take into account. The need is for the user experience for wireless access in public venues. With regard to the download of content, users need to download movies, music, big data sets, and other content in a few seconds rather than minutes or hours in public venues with a large number of users. Currently, users have limited bandwidth access at public venues due to the load placed on access resources. Therefore, there is a gap between the user need for broadband and the ability of current systems to deliver it. The subsystem being contemplated is the antenna and the multiple access approach. In other words, given the needs (gap between current and desired capability), a new subsystem is required to fill the gap. The next few sections describe the application of the six steps to the modified SAI method. 4.6.1

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4.6.2

77

Step 2: Identification of Potential Perturbations

This step identifies things that can interfere with value deliv~~Y. over the lifetime of the system that can be used in later steps to develop 1lmes. These can be changes in the subsystem design, context, or stakeholder needs. They are important because these changes can put value delivery at risk. An ?utput from this step is a table of each perturbation that is categorized accordmg to seven descriptors: type, space, origin, intention, nature, consequence, and effect.

• Type: Three types are considered. The first is a shift, a long-term change in the context of stakeholder needs, which will likely not return to the prior state. The second is a disturbance, which is a short-term cha~ge that requires action for resolution. The third type is a disruption, whICh is a transient change that requires no action for resolution. • Space: This is a description of space the perturbation is occurring. The space can be the design itself, the context of operations, or the needs of stakeholders.

Step 1: Determine Value Proposition and Constraints

This first step is concerned with the documentation of the overall value proposition, constraints, classification of stakeholders, and elicitation of stakeholder value and design space preference, if any exist.

• Origin: This is the source of the perturbation that can be either internal to the subsystem (or system) or external to it.

• Value proposition: The value proposition is a short description that is one sentence long or, at most, a paragraph long. For the broadband data access subsystem, the value proposition is: "Provide a method that enables broadband data delivery in open format public venues such as sporting events and amusement parks."

• Intention: This is the disturbance intentionally initiated by stakeholders. In other words, is it a change that occurred because of the desired resulting effect? The answer is yes, no, or unknown.

• Constraints: These are physical, geographical, organizational, and policy constraints that limit the possible architectures that can be implemented. For the proposed system, a few of them are that the system must be capable of being approved by appropriate government agencies (such as communications authorities, and local building code authorities) and the system must operate in physical areas such as amusement parks and sporting events.

• Effects: These are the effects of the perturbation that will vary depending on the type of subsystem.

• Identification and classification ofstakeholders: During this step, various stakeholder types are distinguished. For the proposed system, a few of the stakeholders are users of the system, owners and operators of the venue, ba&haul access suppliers, system owners, regulatory groups, and system designers. • Elicitation of stakeholder value and design space preferences: Stakeholder value can be obtained by interviewing the stakeholder groups identified in the previous step.

• Nature: Is the perturbation naturally occurring or is it artificial? • Consequence: Will it have a positive, negative, or unknown effect?

These seven descriptors were applied to five identified perturbations as an example and are shown in Figure 4.3. Note chat five types of potential perturbations are shown, although there are many others. For each type, the seven descriptors were determined. This list of perturbations can be used lacer in the process to develop ilities. 4.6.3

Step 3: Identify Desired llities

This step generates a list of potential iii ties that promot~ long-term :7alue delivery of the subsystem. They can be generated from direct express10ns and requests from stakeholders. This can occur during interviews where stakeholder explicitly state desired ilities. Another source is that iii ties can be gene~ated from Step 2 where perturbations were identified. In this case, the perturbanons reveal

Nature

Consequence

Effect

Yes

Artificial

Unknown

Change in value

External

Yes

Natural

Negative

Subsystem state change

Space

Origin

Regulation Shift change

Context

External

Movement Disturbance of user equipment

Context

Name

Type

Intention

Weather

Disruption

Context

External

No

Natural

Negative

Change in value

Comm. disruption

Disturbance

Design

Either

Either

Artificial

Negative

Change in value

Increase in Disturbance user equipment

Context

External

Yes

Natural

Negative

Reduced data rate delivery

Figure 4.3 List of five perturbations to value delivery from the subsystem.

the need for specific ilities. Another source is brainstorming session with the development team, users, and other stakeholders. A hypothetical list of ilities for the proposed system is shown in Figure 4.4. The list is valid ilicies, but the source of the ility is hypothetical since actual stakeholder surveys and brainstorming session were not conducted. 4.6.4 Step 4: Generate Function Alternatives

This step is the generation of subsystem alternatives that have the potential to meet the desired ilities generated in Step 3. In ocher words, a list of multiple function options to implement the subsystem is generated. One approach is to conceive of the subsystem divided into functions. For each function, there may be multiple options. Therefore, the architecture alternatives generated in this

II·

lllltlll

~

Adaptability

The subsystem must adapt to changes in the location of user equipment

Perturbations analysis

Flexibility

The subsystem be able to change states as the number of users and their distribution in space changes

Perturbations analysis

Reliability

79

Phased Array Concept Development Example

Systems Engineering of Phased Arrays

78

The system must function with low failure rates and low .,maintenance

Stakeholder survey

Functionality

The subsystem must have the ability to maintain value delivery over the lifetime of the system

Brainstorming session

Evolva bility

The subsystem must be capable of adapting to changes in user equipment and other context changes

Brainstorming session

Figure 4.4 List of ilities for the user needs and though this list is hypothetical, the ilities themselves are real.

seep are organized according to function and multiple options exist for each function. The option types tend to be technologies such as hardware, algorithms, software, and operations. T he list can be generated during brainstorming meeting with the development team and other stakeholders. While the list should include functional options that have the potential to meet the desired ilities, there should be little preselection of options at this point. In other words, it is best to have a list of more options than it is to eliminate potential options during this step. A list of potential options is shown in Figure 4.5. While the list is hypothetical, the options are real. Note that the list includes two types of functional alternatives, antenna technology options and multiple access options, listed in the third column. Certainly, other options exist for the antenna and for multiple access, but the goal is to show most of the antenna options and a limited list of multiple access options because more than that is not required to demonstrate this step. In a real-world application of this method, there will likely be multiple functions considered, each with its own set of options. 4.6.5

Step 5: Generate Architecture Options

In this step, architectures are generated by combining the various options for each function that were generated in Step 4. The number of architecture options is the product of the number of all function options. In other words, the number of options for each function is counted and then multiplied which can be represented as

Option Name

Description

Function: Antenna or Multiple Access

Fixed Beam antenna

Single fixed antenna beam

Antenna

Switched Beam antenna

Multiple antennas that can be switched in or out independently

Antenna

Multiple MIMD antenna

Multiple antennas used to exploit multi path effects

Antenna

Passive phased array

Single antenna beam formed with analog phases shifters and centrally located amplifiers

Antenna

Analog AESA

Single antenna beam formed with analog phases shifters with amplifiers at each antenna element

Antenna

Digital AESA

Multiple simultaneous digitally formed antenna beams

Antenna

CDMA

Code division multiple access

Multiple access

TOMA

Time division multiple access

Multiple access

Figure 4.5

List of potential options for each function in the subsystem.

Systems Engineering of Phased Arrays

80

Phased Array Concept Development Example n

Number of Architecture Options=

Ila;

(4.1)

i=I

where a;= number of options available for the ith function and n = number of functions in the subsystem. In our example, there are six antenna options and two access options. This means that the maximum number of architecture options is 6 X 2 = 12, and they are listed in Figure 4.6. However, for most any practical syste~, ~ome combinations may not be viable. Therefore, (4.1) provides an upper limit on the number of possible architecture alternatives. 4.6.6

Step 6: Select the "Best" Architecture Option

This step applies a selection methodology to choose the best architecture option. One option is to list the options and generate a list of benefits and drawbacks for each option. In addition, the identified options can be analyzed and ranked by their ability to meet each particular ility. A systematic way to do this is to use a QFD analysis as described in [12]. The same approach is taken here where the ilities are used as criteria for choosing the best architecture option. The same trade study procedure is followed as outlined in Section 1.5.3. Each of the criteria (ility) is given a weighting, Wk, which is related to its importance to the mission of the subsystem. Each of the options is assigned a value, Vi, for its ability to achieve each of the criteria (ility). If this is done, then the score for each option is given by using (1.1) from Chapter 1.

Option Number

Figure 4.6

Access Options

Antenna Options

1

CDMA

Fixed beam antenna

2

CDMA

Switched beam antenna

3

CDMA

Multiple MIMD antenna

4

CDMA

Passive phased array

5

CDMA

Ana log AESA

6

CDMA

Digital AESA

7

TOMA

Fixed beam antenna

~

TOMA

Switched beam antenna

9

TOMA

Multiple MIMO antenna

10

TOMA

Passive phased array

11

TOMA

Analog AESA

12

TOMA

Digital AESA

List of the 12 possible architecture options.

81

Using this approach, a trade study matrix can be developed as shown in Figure 4. 7 for a limited number of available options considered since a full analysis of all 12 options is not necessary to illustrate the technique. From the figure, the table is divided into three sections. The first section lists the options chat are subject to the trade study. In chis case, there are 4 of the possible 12 options that are listed (to save space). The second section shows the value assigned to each option based upon its ability to achieve the ility criteria. This value is assigned based upon testing, simulation, and other methods such as expert opinion and history from deployed solutions. The third section is the trade study results and shows the score for each of the options. As can be seen from the cable, the option of TOMA and digital AESA is scored at 61, which means it is the preferred method. In a real-world analysis, the analysis would consider more of the options and che justification for value assigned for each of che criteria would be provided (i.e., simulation results or similar).

4.7

Conclusions

This chapter describes the application of the modified SAI method for selecting a baseline phased array subsystem. This provides the systems engineer with a process that can be used for selecting the correct baseline design. A hypothetical example is provided demonstrating the method. While the example is hypothetical, the technology options are real as are the ilities. The result shows that the baseline subsystem concept is a digital beamforming phased array chat uses TOMA.

4.8

Problems

Q4. l

For new system development, what is the primary job function of the systems engineer? Provide four ways that this function is different from other engineering disciplines.

Q4.2

Name the two inputs to the concept development phase and describe each in a paragraph of at least 5 sentences.

Q4.3

Summarize the definitions of system architecting provided in Section 4.4 using a paragraph of at least 5 sentences. Do not just repeat the definitions provided. Rather absorb them and synthesize a summary in your own words.

Q4.4

What is the difference between the SAI method and the modified SAI method?

Q4.5

According to the SAI method, what are potential perturbations to a subsystem or system?

Phased Array Concept Development Example

Systems Engineering of Phased Arrays

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direction along the XY plane. The electric field cancels out along the z-axis resulting in a figure-8 shape along the }Z plane. While, ideally, the input impedance for a half-wave dipole is 73Q + jOn at resonance, there is typically a reactive component in one's initial design due to the physical implementation. This reactive can be tuned by decreasing or increasing the dipole length empirically in the laboratory or through 3-D software modeling and analysis tools [3, 4] . Two critical circuit components of a dipole, and other antennas, are impedance matching network and unbalanced to balanced (balun) converter. The impedance matching network converts dipole input impedance to the desired system impedance, which is normally son. For instance, the transmission line system within T/R modules is usually son. The transmission lines in the system and mo1ules are normally unbalanced such as microstrip, stripline, or coax. However, the dipole must be fed with a balanced transmission line. Therefore, the impedance matching network can include the transition from an unbalanced to a balanced transmission line. These transitions are known as baluns. Figures 5.5 and 5.6 illustrate various types of balun configurations used along with their equivalent circuits and transmission line configurations [5-7] .

Figure 5.4

Half-wave dipole rad iation pattern.

While the beam of a dipole is omnidirectional in the H-plane, it is often necessary to focus the antenna beam in one direction. This is done by placing it in front of a metal backplane (often referred as the antenna ground plane) as shown in Figure 5.7. In an array environment, the radiation emitted from an embedded dipole is subjected to coupling from the adjacent dipoles. Figure 5.8 shows a typ~cal 2-D dipole array configuration in front of a back plane. The mutual coupling between elements can affect the dipoles radiation pattern, input impedance, and operating frequency. The impact of chis mutual coupling varies depending on the array size and spacing, frequency, and scan angle. The terms "active impedance" and "active" or "embedded" element patterns are used to distinguish the embedded dipole element performance from the single, self, or isolated dipole element performance. While [1, 2, 8-10] discussed the theory of mut~al coupling between elements within an array, the final determinati~n of the acc_1ve element impedance can be done empirically in the laboratory usmg waveguide simulators [10, 11] or through 3-D software modeling and analysis tools such as HFSS [3] or CST [4] to model the waveguide simulators using the periodic boundary condition and Floquet modes.

5.5

Planar lnverted-F Antenna

Planar inverted-F antenna (PIFA) is a popular antenna element used in mobile phone, Wi-Fi, and loT applications because of its small size and low profile [11,

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