Microwave Circulator Design Second Edition CH00_FM_6417.indd 1 12/19/13 12:14 PM For a listing of recent titles in the Artech House Microwave Library, turn to the back of this book. CH00_FM_6417.indd 2 12/19/13 12:14 PM Microwave Circulator Design Second Edition Douglas K. Linkhart artechhouse.com CH00_FM_6417.indd 3 12/19/13 12:14 PM Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the U.S. Library of Congress. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. ISBN-13: 978-1-60807-583-6 Cover design by Vicki Kane © 2014 ARTECH HOUSE 685 Canton Street Norwood, MA 02062 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 CH00_FM_6417.indd 4 12/19/13 12:14 PM Contents Preface xi Acknowledgments xv 1 Theory of Operation 1 1.1 Units, Conversions, and Symbols 1 1.2 The Physical Basis of Ferrimagnetism 4 1.3 Ferrimagnetic Resonance 11 1.4 Microwave Propagation in Ferrites 15 1.5 Other Technologies 29 1.5.1 Semiconductor Circulators 29 1.5.2 Nanotechnology Circulators 30 1.5.3 Thin Ferrite Films 31 1.5.4 Active Circulators 32 2 Circulator Specification 35 2.1 The Parameters 35 2.2 Reflections and Segmentation 48 2.3 Junction Circulators 52 vv CH00_FM_6417.indd 5 12/19/13 12:14 PM vi Microwave Circulator Design 2.3.1 Single- Ferrite (Non- Composite) Junction Circulators 54 2.3.2 Composite- Ferrite Junction Circulators 56 2.4 Lumped- Constant Circulators 56 2.5 Differential Phase Shift Circulators 58 2.6 Switching Circulators 60 2.7 Okada Circulators 61 2.8 Field- Displacement Isolators 61 2.9 Resonance Isolators 64 3 Applications of Circulators 69 3.1 Load Isolation 69 3.2 Duplexing 71 3.3 Multiplexing 76 3.4 Parametric Amplifiers 77 3.5 Phase Shifting 81 4 Material Selection 87 4.1 Ferrites 87 4.1.1 Ferrite Classes 87 4.1.2 Ferrite Manufacturing 88 4.1.3 Design Considerations 90 4.1.4 Test Methods 91 4.1.5 Specifications 93 4.1.6 Temperature Effects 93 4.1.7 Ferrite Selection 96 4.2 Magnet Selection 100 4.3 Magnetic Compensating Material Selection 102 4.4 Dielectric Selection 103 4.5 Metals Selection 104 CH00_FM_6417.indd 6 12/19/13 12:14 PM Contents vii 5 Electrical Design 107 5.1 Junction Circulators 107 5.1.1 Basic Principles 107 5.1.2 Historical Papers 111 5.1.3 Above- Resonance Approximations 125 5.1.4 Below- Resonance Approximations 130 5.1.5 Network Synthesis 132 5.1.6 Center Conductor Geometries 143 5.1.7 Waveguide Junction Geometries 149 5.1.8 Stripline Circulator Synthesis Algorithm 153 5.1.9 Microstrip Circulator Synthesis Algorithm 157 5.1.10 Waveguide Junction Circulator Synthesis Algorithm 161 5.1.11 Okada Circulators 163 5.1.12 Circulators Having Composite Ferrites 165 5.2 Lumped- Constant Circulators 167 5.3 Differential Phase Shift Circulators 171 5.4 Resonance Isolators 177 5.5 Dummy Loads for Isolators 179 5.6 Temperature Effects 181 5.7 Intermodulation Distortion 186 5.8 RF Power Effects 187 5.8.1 Steady- State Thermal Effects 187 5.8.2 Transient Thermal Effects 191 5.8.3 Voltage Breakdown 193 5.8.4 Spin- Wave Instability 198 6 Magnetic Design 205 6.1 Magnet Sizing 205 6.1.1 Ferrite Demagnetization Factors 207 6.1.2 Leakage Flux Approximation 213 6.1.3 Approximate Design of Magnetic Circuits 214 CH00_FM_6417.indd 7 12/19/13 12:14 PM viii Microwave Circulator Design 6.1.4 Simulation of Magnetic Circuits 217 6.2 Shielding 219 6.3 Temperature Compensation 221 6.4 Completing the Circuit 223 6.5 Special Cases 225 6.5.1 Switching Circulators 225 6.5.2 Self-Biased Circulators 228 6.5.3 Considerations for Microstrip Circulators 228 7 Mechanical Design 231 7.1 Thermal Considerations 231 7.1.1 Stripline Power Handling 231 7.1.2 Power Dissipation in Ferrites 233 7.1.3 Cooling of Ferrites 234 7.2 Venting 235 7.3 Coaxial Junction Circulators 237 7.3.1 Packaging Techniques 237 7.3.2 Dimensional Tolerances 242 7.3.3 Controlling Cavity Resonances 244 7.3.4 Transitions 249 7.3.5 RFI Control 253 7.3.6 Dissimilar Metals 253 7.3.7 Finishes 253 7.4 Lumped-Constant Circulators 254 7.5 Waveguide Circulators 256 7.6 Resonance Isolators 258 8 Assembly and Testing 261 8.1 Assembly Techniques 261 8.2 Testing 268 8.2.1 Finding the Operating Point 268 CH00_FM_6417.indd 8 12/19/13 12:14 PM Contents ix 8.2.2 Taking Data 271 8.2.3 RF Power Testing 272 8.2.4 Intermodulation Testing 272 8.2.5 Multipaction Testing 273 8.2.6 Magnetic Moment Measurement 275 8.2.7 Measurement Uncertainty and Gauge Studies 276 9 Tuning 281 9.1 Interaction Between Magnetic and Electrical Adjustments 281 9.2 Magnetic Adjustment 281 9.2.1 Above-Resonance Magnetic Adjustment 282 9.2.2 Below-Resonance Magnetic Adjustment 283 9.2.3 Magnet Charging, Calibration, and Stabilization 283 9.3 Electrical Adjustment 285 9.4 Eigenvalue Evaluation 295 10 Design Examples 301 10.1 Introduction to Examples 301 10.2 Above-Resonance Stripline Junction Circulator 302 10.3 Below-Resonance Stripline Junction Circulator 311 10.4 Waveguide Junction Circulator 319 10.5 Microstrip Circulator 324 10.6 Differential Phase Shift Circulator 329 10.7 Lumped-Constant Circulator 333 List of Symbols 339 Frequently Used Equations 347 About the Author 351 Index 353 CH00_FM_6417.indd 9 12/19/13 12:14 PM