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A Calibration Free Vector Network Analyzer Scholars' Mine Masters Theses Student Theses and Dissertations Summer 2013 A calibration free vector network analyzer Arpit Kothari Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses Part of the Electrical and Computer Engineering Commons Department: Recommended Citation Kothari, Arpit, "A calibration free vector network analyzer" (2013). Masters Theses. 7125. https://scholarsmine.mst.edu/masters_theses/7125 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. i A CALIBRATION FREE VECTOR NETWORK ANALYZER by ARPIT KOTHARI A THESIS Presented to the Faculty of the Graduate School of the MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE IN ELECTRICAL ENGINEERING 2013 Approved by Dr. Reza Zoughi, Advisor Dr. Daryl Beetner Dr. David Pommerenke ii 2013 Arpit Kothari All Rights Reserved iii ABSTRACT Recently, two novel single-port, phase-shifter based vector network analyzer (VNA) systems were developed and tested at X-band (8.2 - 12.4 GHz) and Ka-band (26.4 – 40 GHz), respectively. These systems operate based on electronically moving the standing wave pattern, set up in a waveguide, over a Schottky detector and sample the standing wave voltage for several phase shift values. Once this system is fully characterized, all parameters in the system become known and hence theoretically, no other correction (or calibration) should be required to obtain the reflection coefficient, (Γ), of an unknown load. This makes this type of VNA “calibration free” which is a significant advantage over other types of VNAs. To this end, a VNA system, based on this design methodology, was developed at X-band using several design improvements (compared to the previous designs) with the aim of demonstrating this "calibration-free" feature. It was found that when a commercial VNA (HP8510C) is used as the source and the detector, the system works as expected. However, when a detector is used (Schottky diode, log detector, etc.), obtaining correct Γ still requires the customary three-load calibration. With the aim of exploring the cause, a detailed sensitivity analysis of prominent error sources was performed. Extensive measurements were done with different detection techniques including use of a spectrum analyzer as power detector. The system was tested even for electromagnetic compatibility (EMC) which may have contributed to this issue. Although desired results could not be obtained using the proposed standing-wave-power measuring devices like the Schottky diode but the principle of “calibration-free VNA” was shown to be true. iv ACKNOWLEDGEMENTS I am aware that this thesis would never have been possible without the generous help that I received from various quarters. My greatest debt of gratitude is to my supervisor, Professor Reza Zoughi for his illuminating guidance, constructive criticism and for making available to me the amntl lab and all the resources necessary to conduct my research. I am deeply indebted to Dr. David Pommerenke and Dr. Daryl Beetner for their insightful suggestions and invaluable assistance during the course of my research. My very special thanks to Dr. Mohammad Tayeb Ghasr for his motivating guidance, constant encouragement, unfailing patience and support all through my research. I am grateful to the IEEE I&M society for the 2011 Graduate Fellowship Award which provided me with the financial assistance while doing this research. I would like to record my appreciation of the Curtis Laws Wilson Library, which supplied me with important books, journals, and articles and to the University Librarians, who provided valuable help at the various stages of my work. My thanks also to my lab colleagues, Mark, Mojtaba, Toby and all the others for the wonderful and enlightening discussions and episodes of Futurama. But for the unwavering faith and steadfast support of my parents and my brother, I would not have been able to complete this work. I am indeed very thankful to them and to my family members for the moral support I always received from them. v This work is dedicated to my late revered grandmother Shrimati Madan Kunwar Kothari. (May 25, 1925 – Mar 14, 2013) vi TABLE OF CONTENTS Page ABSTRACT ....................................................................................................................... iii ACKNOWLEDGEMENTS ............................................................................................... iv LIST OF ILLUSTRATIONS ............................................................................................. ix LIST OF TABLES ........................................................................................................... xiv SECTION 1. INTRODUCTION .............................................................................................. 1 1.1. VECTOR NETWORK ANALYZERS (VNAs) ................................................ 1 1.1.1. Background. ............................................................................................. 1 1.1.2. RF Detection. ........................................................................................... 2 1.1.3. One-Port VNAs. ....................................................................................... 3 1.1.4. Previous Work. ...................................................................................... 5 1.1.5. Current Work. ......................................................................................... 7 2. SYSTEM DESIGN ........................................................................................... 10 2.1. INTRODUCTION ............................................................................................ 10 2.2. -20 dB COUPLER ............................................................................................ 11 2.3. PHASE-SHIFTER ............................................................................................ 15 2.3.1. Phase-Shifter Design. ............................................................................. 15 2.4. DETECTOR CHARACTERIZATION ............................................................ 17 3. SYSTEM MODELING AND CALIBRATION .............................................. 20 3.1. INTRODUCTION ............................................................................................ 20 3.2. CALCULATION OF Γ BASED ON PHASE SHIFT ..................................... 20 3.3. ITERATIVE Γ ESTIMATION ........................................................................ 21 3.3.1. System Model ........................................................................................ 21 3.3.2. Testing with Several DUTs. ................................................................... 24 3.3.3. Estimation of Γ ....................................................................................... 26 3.4. CALIBRATION ............................................................................................... 27 3.5. FACTORS AFFECTING PERFORMANCE .................................................. 30 3.6. EFFECT OF LOW PHASE SHIFT.................................................................. 31 vii 4. SENSITIVITY ANALYSIS ............................................................................. 36 4.1. INTRODUCTION ............................................................................................ 36 4.2. METHODOLOGY ........................................................................................... 36 4.3. SIMULATION AND ANALYSIS ................................................................... 39 4.3.1. Signal-to-Noise Ratio (SNR). ................................................................ 39 4.3.2. Loss in Phase-Shifter. ............................................................................ 41 4.3.3. Total Phase Shift. ................................................................................... 42 4.3.4. Scaling Constant C. ................................................................................ 43 4.3.5. Detector Slope. ....................................................................................... 45 4.4. PERFORMANCE COMPARISON WITH COMMERCIAL VNA ................ 47 4.5. SUMMARY ..................................................................................................... 49 5. MEASUREMENTS ......................................................................................... 50 5.1. INTRODUCTION ............................................................................................ 50 5.2. ALTERNATIVE DETECTION AND DAQ METHODS ............................... 51 5.3. HP8510C VNA USED AS DETECTOR ......................................................... 52 5.3.1. HP8510C VNA with Full 2-port Calibration. ........................................ 53 5.3.2. HP8510C VNA with Response Calibration. .......................................... 56 5.3.3. HP8510C VNA is Un-calibrated. .......................................................... 57 5.3.4. b2 Measurements. .................................................................................. 62 5.3.5. Air as a Standard. ................................................................................... 63 5.3.6. S-parameter Correction and Verification.
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