Donadio, Oberdan (2012) G-band waveguide to microstrip transition for MMIC integration. PhD thesis. http://theses.gla.ac.uk/3354/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] G-band Waveguide to Microstrip Transition for MMIC Integration by Oberdan Donadio Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in the School of Engineering College of Science and Engineering January 2012 Declaration of Authorship I, Oberdan Donadio, declare that this thesis titled, `G-band Waveguide to Microstrip Transition for MMIC Integration' and the work presented in it are my own. I confirm that: This work was done wholly or mainly while in candidature for a research degree at the University of Glasgow. Where any part of this thesis has previously been submitted for a degree or any other qualification at this University or any other institution, this has been clearly stated. Where I have consulted the published work of others, this is always clearly at- tributed. Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this thesis is entirely my own work. I have acknowledged all main sources of help. Where the thesis is based on work done by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself. Signed: Oberdan Donadio Date: 02/09/2011 i \A smooth sea never made a skillful mariner" (English proverb) Abstract In recent years, Millimetre-Wave (MMW) frequencies (30-300 GHz) have been exploited for a variety of attractive applications such as astronomical observation, medical imag- ing, aircraft aided-control landing, security and concealed weapons detection. All this was also possible thanks to the advances in high frequency circuits where Monolithic Microwave Integrated Circuits (MMICs) represent a key factor. Systems working at MMW often use metal waveguides as interconnect elements and transitions are em- ployed to transfer the signals from these elements to the Radio Frequency (RF) circuits. The objective of this thesis is to design, fabricate and characterise electromagnetic tran- sitions between rectangular waveguide (WR) and planar transmission lines at G-band frequencies (140-220 GHz). The first part of this work presents an overview of the elec- tromagnetic properties of the atmosphere at MMW frequencies and their use for passive MMW imaging applications. Fundamental design concepts and prototypes of real-time imagers are also represented, based on the pioneering work carried out at QinetiQ Ltd. An extensive review of the scientific literature on waveguide transitions presents previous designs and architectures. The work proceeds through design, simulation, fabrication and measurements of G-band transitions highlighting advantages and disadvantages of different structures. The novel design of Elevated E-plane probes, used as waveguide to microstrip transitions in this work, extends the fabrication technique of MMIC air-bridges to build suspended metal structures and provides an additional optimising parameter to improve the reflec- tion performance of the transition by decomposing the substrate influence on the metal probe. The innovative Elevated E-plane probe is fabricated on Semi-Insulated Gallium Arsenide (SI-GaAs) and it is MMIC-integrated, reducing system complexity and optimizing fab- rication and assembly costs. The core of the thesis details the fabrication processes and procedures and a separate section describes the manufacture of G-band rectangular waveguide blocks that host the transitions. The overall fabrication is carried out using in-house facilities at the Univer- sity of Glasgow without the aid of external facilities. Measured results are presented and discussed, validating design and simulations. This work has led to a successful design and fabrication of GaAs-integrated rectangular waveg- uide to microstrip line transition at G-band. Acknowledgements The investigation which is the subject of this Thesis was financially supported by EPSRC and QinetiQ Ltd. and was carried out as CASE award under the terms of QinetiQ Agreement No. 45358. I would like to express my gratitude to my supervisor Dr. Khaled Elgaid for giving me the great opportunity of this Research project at the University of Glasgow and for his insightful guidance and advices throughout its course. I'm also particularly grateful to Dr. Roger Appleby, my industrial supervisor, who gave me the chance to collaborate with QinetiQ and for the fruitful discussions and meetings we had during the course of the project. Thanks to QinetiQ Ltd who contributed to support the research and allowed me to publish its results. Extra special thanks to Prof. Iain Thayne, my second supervisor, for his encouragements and useful feedbacks. I would like to thank Susan Ferguson for introducing me to fabrication, for support and for being always an important source of information when needed. Special thanks to the Ultrafast group and to Helen Mclelland for helping during fabrication processes. Thanks to Wilson MacDougall, from the Mechanical Workshop, for his help in operating the CNC milling machine during the fabrication of my waveguides. I particularly thank Alex Ross for helping me in the substrate thinning and for all the interesting conversations we had. Thank you Alex. No acknowledgement would be complete without mentioning Dr. Gabor Mezosi, whom I thank for sharing his points of view and for his continuous encouragement. He has been a colleague and a precious friend. Thanks to Dr. Michael Strain for his guidance and valuable comments. I wish to thank the wonderful people from the JWNC, they are too many to list but I will remember you all. I also thank all nice friends I had around at the department, Lai Bun, Chi Jeon, Adel, Ian, Antonio, Giuseppe, Carla, Philippe, Giangiacomo, Marc, Corrie, Barry and please forgive me if I forgot someone..... On a personal note, I want to thank my family for supporting me in my choices and for always being there when I needed. Finally, from the bottom of my heart I want to thanks Neus, who has always been by my side and helped me during my hardest moments. I could not have finished this work without her help! Thank you all! iv Publications and Events Aspects of the work described in this Thesis has been published or presented in following papers and internal events: • O. Donadio, K. Elgaid, and R. Appleby, "Waveguide-to-microstrip transition at G-band using Elevated E-plane Probe" Electronics Letters, 47(2), pp.115-116, January 2011. • O. Donadio, K. Elgaid, "Fabrication of Broadband waveguide-to-microstrip tran- sition at G-band", Postgraduate Student Colloquium, University of Glasgow, 2009. • O. Donadio, K. Elgaid, "MMW Waveguide-to-planar Transmission line Design", Postgraduate Student Conference, 1st winner Posters Session, Heriot-Watt Uni- versity Edinburgh, 2008. Contents Declaration of Authorshipi Abstract iii Acknowledgements iv List of Figures ix List of Tables xiii Abbreviations xiv 1 Introduction1 1.1 Introduction...................................1 1.2 An Overview of Millimetre Waves.......................1 1.2.1 Atmospheric Absorption........................2 1.3 Millimetre Wave Imaging...........................6 1.4 Passive Millimetre-Wave (PMMW) Imaging................8 1.4.1 Contrast Model and Materials Properties..............9 1.4.2 System Performance.......................... 12 1.4.3 Different Systems............................ 15 1.5 Trends towards Higher Frequencies...................... 19 1.6 Conclusions................................... 20 2 Rectangular Waveguide to Planar Transmission Line Transitions 21 2.1 Introduction................................... 21 2.2 Aspects of Propagation in Rectangular Waveguide............. 22 2.2.1 Low Loss Transmission Line...................... 22 2.2.2 Rectangular Waveguide Dimensions and Frequency Bands..... 22 2.3 Architecture of the Transitions........................ 22 2.3.1 Ridge-Waveguide Transitions..................... 24 2.3.2 Aperture-coupled Transitions..................... 26 2.3.3 Transversal Transitions........................ 31 2.3.4 In-Line Transitions........................... 35 2.4 Some Considerations.............................. 40 vi Contents vii 2.5 Conclusions................................... 41 3 Design and Methods 45 3.1 Introduction................................... 45 3.2 Electromagnetic Design using EDA Software Packages........... 46 3.2.1 HFSS, FEM and Adaptive Meshing................. 46 3.2.2 Simulation setup............................ 49 3.2.2.1 Materials assignment.................... 49 3.2.2.2 Excitations.......................... 49 3.2.2.3 Boundaries.......................... 50 3.2.2.4 Analysis Setup........................ 50 3.2.2.5 Custom Meshing Operations................ 51 3.3 Design Specifications.............................. 51 3.3.1 Considerations on Design options..................