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Design of an Orthomode Transducer in Gap Waveguide Technology Master of Science Thesis in the Program Communication Engineering

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Design of an Orthomode Transducer in Gap Waveguide Technology Master of Science Thesis in the Program Communication Engineering Design of an Orthomode Transducer in Gap Waveguide Technology Master of Science Thesis in the program Communication Engineering ALI IMRAN SANDHU Antenn Group, Department of Signals & Systems Chalmers University of Technology Göteborg, Sweden, September 2010 The Author grants to Chalmers University of Technology the non-exclusive right to publish the Work electronically and in a non-commercial purpose make it accessible on the Internet. The Author warrants that he/she is the author to the Work, and warrants that the Work does not contain text, pictures or other material that violates copyright law. The Author shall, when transferring the rights of the Work to a third party (for example a publisher or a company), acknowledge the third party about this agreement. If the Author has signed a copyright agreement with a third party regarding the Work, the Author warrants hereby that he/she has obtained any necessary permission from this third party to let Chalmers University of Technology store the Work electronically and make it accessible on the Internet. Design of an Orthomode Transducer in Gap Waveguide Technology ALI IMRAN SANDHU c ALI IMRAN SANDHU, 2010 Examinar: Prof. Per-Simon Kildal Technical report no 2010:xx Antenna Group, Department of Signals & Systems Chalmers University of Technology SE-41296 Gteborg Sweden Telephone +46 (0) 31-772 1000 Cover: Picture shows the 3D OMT strucuture with magnitude E field inside, simu- lated in HFSS Antenna Group, Department of Signals & Systems Gteborg, Sweden September 2010 I would like to dedicate my work to my family. I believe that I have made it possible merely due to the prayers and great moral support from my parents throughout my stud- ies. Special dedications to my daughter and my wife for their patience and support being away from me. Acknowledgements I owe my deepest gratitude to all of those who made this thesis possible. I would like to thank • Professor Per-Simon Kildal for his confidence in me that I could complete this master project and his excellent supervision. He provided tremendous support, guidance, and motivation throughout this project. Thanks for always having time to answer questions and replying to emails almost instantaneously. It has been a rewarding and unique experience to work and study under your supervision! • Professor Ahmed A.Kishk for being so nice and devoted towards my thesis progress. I have always found him clearing my concepts, even during weekends and late at evenings. I must appreciate his 3D drawing capabilities, which helped me a lot to visualise and implment the designs. I am very thankful for his sincere guidance regarding my thesis work and future studies. • Dr. Jian Yang, without whom's support this thesis would not have been possible. I have always felt comfortable in bothering him for discussions related to my thesis work and future studies as well. I would like to appreciate his sincere guidance related to the antenna course. He was not related to my master thesis, even then he always assisted me on issues related to HFSS simulations and theoratical concepts. I cannot limit my gratitude for him in words. • Anders Edquist from Ansoft support. He has always assisted me in resolving complex as well as very basic issues related to my simulations. He always replied my emails frequently with detailed images and technical notes which helped me in learning the software to a greater extent. • Ashraf for his support. Elenna has been a very nice office mate. She has assisted me in clarifying many concepts. I will remember her laughters. • The fellow students and the faculty members who made MPCOM program an interesting yet an enjoyable course. A very special thanks to the Chalmers admis- sion council, who gave me an opportunity to pursue my master studies, and for providing me more than enough resources to utilize. I will treasure the friendships and memories that I have taken from here. iii Abstract Ortho-mode transducer (OMT) is a waveguide structure capable of discriminating two independent signals of the orthogonal dominant modes provided at the common equip- ment port and supplying them to the fundamental mode of the allocated single signal in- terface ports, maintaining a good match at all electrical ports and high cross-polarization discrimination between the independent signals. Gap waveguide is a new waveguide technology recently introduced in [1] and experimen- tally verified in [2]. It is formed inside the gap between the two metallic surfaces one of which is provided with a texture or thin multilayer structure that is used to realize conducting ridges surrounded by a high impedance surface of some kind, which might ideally be a PMC surface. Gap waveguides have made use of bed of nails [3], as a high impedance surface for parallel plate mode suppression, which has resulted in a band stop for more than an octave bandwidth(2:1). Since wave propagation is made prohib- ited in any arbitrary direction other than the conducting ridge, mechanical joints can be applied far away from the propagation path.This gives very good electrical perfor- mance, since it prevents leakage of electromagnetic energy even at high frequencies such as for millimeter and sub millimeter waves, when waveguides are manufactured in two pieces.Gap waveguides are planner and much cheaper to manufacture as compared to hollow waveguides, furthermore they have been very promissing, being very wide band and low loss than alternative so called substrate integrated waveguides(SIW). Arkivator telecom has shown interest in the gap waveguide technology, therefore in col- laboration with Chalmers, Arkivator telecom has provided an opportunity to investigate whether if the design of passive microwave devices in gap waveguide technology is prac- tically realizable, along with a good overall electrical performance. An OMT in gap waveguide technology has been designed, optimized, and simulated for approximately 7 percent bandwidth centered at 42 GHz. The simulations have been done using HFSS. The device exhibits a return loss better than 28dB and isolation better than 35dB for the desired frequency band. The device has shown excellent circular polarization perfor- mance even better than the existing standard waveguide based alternatives. The axial ratio was found to be below 0.2dB with a cross polar isolation better than 40dB. iv Preface This thesis is submitted in partial fulfilment of the requirements for a Master's Degree in communication engineering at Chalmers University of Technology. It contains work done from January to August 2010. My supervisors on this project were Prof. Per-Simon Kildal,Chalmers University of Technology and Prof. Ahmed A. Kishk, University of Mississippi. This thesis has been made solely by the author; most of the text however, is based on the research of Prof. Per-Simon and his research group, and I have done my best to provide references for these sources. This thesis is based on designing, simulating and measuring an orthomode transducer (OMT) in the recently introduced gap waveguide technology, which has proved to be very wide band and less lossy. The major advantage of the ridge gap waveguide as compared to hollow waveguides is that they are planner and much cheaper to manufacture, in particular at high frequencies such as for millimetre and sub millimetre waves. The latter is due to the fact that there are no mechanical joints required, across which electric currents must float. Arkivator Telecom has shown interest in the newly introduced gap waveguide technology; therefore in collaboration with Chalmers, Arkivator Telecom has provided an opportunity to investigate whether if the design of passive microwave devices in gap waveguide technology is practically realizable, along with a good overall electrical performance. This OMT design is among several other projects in pipeline, funded and industrially supported by Arkivator Telecom. This dissertation presents the essential theoratical context along with a few physically realizeable alternatives based on extensive simulations to design the OMT in the gap wavegudie technology. Furthermore the report is structured, so that every chapter is ded- icated to an individual component associated with the OMT. The Introduction(Chapter 1) presents information on the device's electrical performance requirements along with a brief discription of various frequently used technical terminologies. Chapter 2 (Ortho- mode Transducer) covers fundamental concepts to understand the working principle of an OMT. Chapter 3 (Gap Waveguide) describes the principle, operation and detailed analysis of gap waveguides along with a brief introduction to PMC realization approaches. Most of the context of this chapter is taken from the research of Prof.Per Simon Kildal and his v fellow researchers. Chapter 4 and Chapter 5 describes a brief theortical content relaated to septum polarizers and quarter wave plates respectively. Chapter 6 is dedicated to the design and simulations for individual components asso- ciated with the OMT. In addition to the simulations, a comparative discussion for a few alternatives in terms of performance and fabrication limitations has been included also. Chapter 7 presents the re-optimized designs that incorporate all necessary fabri- cation tolerances. These designs have been placed forward for fabrication. The results presented in this chapter are expected to produce a very close agreement with the pro- totype's measurements. This last chapter is followed by Conclusion, summarizing the so far progress
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