University of Colorado, Boulder CU Scholar Electrical, Computer & Energy Engineering Electrical, Computer & Energy Engineering Graduate Theses & Dissertations Spring 4-1-2014 Low-Profile Antennas for Wideband Transmit Application in HF/UHF Bands Rohit Sammeta University of Colorado Boulder, [email protected] Follow this and additional works at:https://scholar.colorado.edu/ecen_gradetds Part of theElectromagnetics and Photonics Commons Recommended Citation Sammeta, Rohit, "Low-Profile Antennas for Wideband Transmit Application in HF/UHF Bands" (2014).Electrical, Computer & Energy Engineering Graduate Theses & Dissertations. 92. https://scholar.colorado.edu/ecen_gradetds/92 This Dissertation is brought to you for free and open access by Electrical, Computer & Energy Engineering at CU Scholar. It has been accepted for inclusion in Electrical, Computer & Energy Engineering Graduate Theses & Dissertations by an authorized administrator of CU Scholar. For more information, please [email protected]. LOW-PROFILE ANTENNAS FOR WIDEBAND TRANSMIT APPLICATIONS IN HF/UHF BANDS by Rohit Sammeta B.Tech, Indian Institute of Technology-Bombay, Mumbai, INDIA, 2004 M.S., University of Mississippi, Oxford, MS, 2007 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Electrical, Computer, and Energy Engineering 2014 This thesis entitled: Low-Profile Antennas for Wideband Transmit Applications in HF/UHF Bands written by Rohit Sammeta has been approved for the Department of Electrical, Computer, and Energy Engineering Dejan S. Filipović W. Neill Kefauver Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. Rohit Sammeta (Ph.D., Electrical Engineering) Low-Profile Antennas for Wideband Transmit Applications in HF/UHF Bands Thesis directed by Prof. Dejan S. Filipović Frequency Independent (FI) antennas have impedance and far-field properties that remain largely invariant with frequency making them an excellent choice for wideband applications. The need for polarization diversity prompts the use of 4-arm sinuous or 4-arm log-periodic FI apertures that can radiate dual-CP over the full bandwidth. The 4-arm sinuous is almost always backed with carbon loaded absorber limiting its use to receiving or low-power transceiver use. Similarly the 4-arm log-periodic antenna suffers from twice the size requirement as compared to the spiral or the sinuous. The sinuous and log-periodic antennas that are commercially available or reported in literature are rated only for low powers (2 - 10 W) and are not low-profile especially in the UHF band. The need for low profile antennas extends to the HF band also where antennas capable of transmitting with large instantaneous bandwidths are needed. It is this need for transmit capable low profile antennas in HF/UHF bands that this thesis addresses. The development of low-profile antennas for transmit applications in the parts of UHF (500 MHz – 3 GHz) and HF (2 MHz – 10 MHz) bands is presented. In the UHF band, 4-arm sinuous and 4-arm planar log-periodic (LP) antennas are chosen for their wideband dual circular polarized (CP) FI performance. Various techniques like dielectric lens-loading, lossless cavity-backing with integrated matching network, ferrite-tiled cavity-backing, and ferrite-tiled ground plane backing are incorporated to convert the inherently bidirectional sinuous aperture into low-profile, flush-mountable, efficient, unidirectional antennas with dual CP capability. The developed prototypes are fabricated, characterized, and shown to be capable of transmitting 10 times higher power than conventional sinuous antennas while maintaining thermal and electromagnetic stability. iii A novel method to halve the size of a 4-arm planar log-periodic aperture for dual CP performance is introduced. The size reduction is achieved by coupling the currents from the booms of the LP to an annular ring resulting in a ring-turnstile-LP composite aperture. This novel aperture is fabricated, characterized and is shown to be a highly desirable antenna for dual CP applications due to its small size, simple beamformer, and dual CP capability over the same bandwidth. The proposed concept is implemented in slot configuration and the resulting ring-turnstile-slot LP is developed and fabricated. Through both low-power and high power characterizations, the antenna is shown to be a low profile bidirectional antenna capable of transmitting hundreds of Watts of CW power. A reconfigurable antenna configuration of a horizontal dipole and a vertical loop is proposed to achieve bandwidths close to 24 KHz for NVIS communication in the HF band. The antenna is designed to be used with the Amphibious Assault Vehicle (AAV) and is low- profile with NVIS compatible radiation patterns throughout the frequency band. The vertical loop is operated in the lower frequencies and the horizontal dipole at higher frequencies in the HF band and the effects of real grounds, wire diameter and the AAV’s tracks on the achieved bandwidth, gain, efficiency, and input resistance are illustrated. Various studies involving the effect of the grounds, position of the antenna above the roof of the AAV, and effect of the AAV’s presence on the performance of horizontal dipole and horizontal loop antennas is also detailed. The results presented in this thesis and the antennas developed herein should pave the way for use of sinuous antenna in efficient transmit applications for the first time, and the use of the log-periodic antenna for dual-CP transmit applications alongside the spiral or the sinuous in its novel reduced size form, while maintaining hundreds of Watts of CW power capability in the UHF band for both the antennas. The reconfigurable antenna in the HF band should provide an excellent starting configuration for achieving large bandwidths for NVIS transmit applications requiring high data rates. iv Dedication To my parents, Ramprasad Sammeta and Sarada Sammeta. Acknowledgements I would like to express my sincere gratitude to my advisor Prof. Dejan Filipović for his unwavering support and guidance through the course of my PhD. Filip has been invaluable to the process of shaping my work into its present form. He has constantly provided me with ideas and encouragement, and his work ethic and zeal have been an inspiration to me. Filip let me get as much as I wanted to from the PhD process and for that I consider myself lucky to have been his student. Apart from his professional support, he has been very supportive and understanding of the personal hardships I had to face during this time. Simply put, I could not have had a better advisor. I want to thank the members of my comprehensive and defense thesis committee: Prof. Zoya Popović, Prof. Edward Kuester, Prof. Scott Palo, and Dr. Neill Kefauver for their time and efforts to evaluate and improve my research. Special acknowledgement is owed to Dr. Kefauver for his thorough and complete review of this thesis. His comments and suggestions have greatly improved this work. The courses I have taken with Prof. Popović and Prof. Kuester have added considerably to my knowledge base and I thank them for that too. A big thank you to all the graduate students and postdoctoral fellows from the Antenna Research Group; especially, Dr. Matthew Radway, Dr. Joseph Mruk, Dr. Mohamed Elmansouri, Dr. Maxim Ignatenko, Dr. Nathan Sutton, Nathan Jastram, James Bargeron, Jaegeun Ha, and Saurabh Sanghai for their help with measurements and fruitful technical conversations. A special thanks to Mohamed for being a great friend and also helping out immensely with all the time domain characterizations presented in this thesis. Thank you to Timothy Samson, Dr. Hongyu (Eric) Zhou, David Lopez, Sushant Shrestha, and Dr. Muhanned Tarifi, for being awesome labmates. vi Nathan Jastram, Scott Schafer, and Jennifer Imperial have been great friends during these PhD years. They have my gratitude for all the beer, burger, and movie nights and various shenanigans that helped me unwind and keep my sanity. Nate especially for the company he kept while often working late into the night (until his marriage i.e. ;)), Scott for helping me learn some key concepts, and Scott and Jennifer for indulging in my ramblings about the world and all that is beautiful and ugly about it. I have been fortunate to have made great friends over the course of my life. There are far too many to list them all here so I will just say a big thank you to everyone! However two stand out, Zubin Jacob and Dheeraj (Golu) Singaraju. I have shared some of the best times in my life with them and know that I can always count on their support and company. To put it eloquently, they are my bros! So a special thanks to Zubin and Golu. Last but most importantly, I want to thank my family. My parents especially, for everything they have done for me. I am who I am today largely due to their unconditional love and support. My father has been my biggest influence. I learnt the importance of fearlessness, hard work and single-minded dedication from him. Losing him has been a very big blow and I hope I make him proud with what I do in my life. From my mother I learnt the virtues of being a patient and caring person. Her love and affection mean a lot to me. This is why this thesis is dedicated to them. My little sister Shilpa has always been supportive of me in one form or other and for that I thank her sincerely. Of course, a big thank you to my beautiful wife Priya who has stood by me during the critical periods of my PhD with her love and support. She is an important source of happiness in my life and I look forward to continue making many wonderful memories with her. vii Table of Contents Chapter 1 Introduction ............................................................................................................................ 1 1.1 Overview of Frequency Independent (FI) Antennas .......................................................... 1 1.2 Overview of HF Antennas .................................................................................................. 3 1.3 Thesis Motivation ............................................................................................................... 4 1.3.1 The Need for Wideband Antennas ............................................................................... 4 1.3.2 Advancement of Transmit Capabilities ....................................................................... 5 1.3.3 Low-Profile Characteristics ......................................................................................... 5 1.4 Thesis Organization ........................................................................................................... 6 2 Lens Loaded Cavity Backed Transmit Sinuous Antenna ............................................. 10 2.1 Introduction .......................................................................................................................10 2.2 Basic Sinuous Aperture .....................................................................................................12 2.3 Antenna Design .................................................................................................................15 2.3.1 Sinuous Aperture ........................................................................................................15 2.3.2 Dielectric Lens Loading ..............................................................................................16 2.3.3 Cavity Backing ............................................................................................................21 2.3.4 Beamformer Network ..................................................................................................24 2.4 VSWR and Far-Field Characterization .............................................................................26 2.5 High Power Test ................................................................................................................32 viii 2.6 Discussion ..........................................................................................................................37 2.7 Comparison with Conical Sinuous Configuration ............................................................39 2.8 Summary ...........................................................................................................................43 3 Efficient Lens Loaded Cavity Backed Sinuous Antenna .............................................. 45 3.1 Introduction .......................................................................................................................45 3.2 Antenna Design .................................................................................................................47 3.2.1 Cavity Study ................................................................................................................47 3.2.2 Matching Network ......................................................................................................50 3.3 Antenna Assembly .............................................................................................................54 3.4 VSWR and Far-Field Characterization .............................................................................57 3.5 High Power Test ................................................................................................................62 3.5.1 High Power Test Method ............................................................................................62 3.5.2 Failure Analysis ..........................................................................................................66 3.6 Time Domain Analysis ......................................................................................................70 3.7 Boresight Directivity Dip ..................................................................................................73 3.8 Discussion and Summary ..................................................................................................75 4 Lens Loaded Ground Plane Backed Sinuous Antenna ................................................. 79 4.1 Introduction .......................................................................................................................79 4.2 Antenna Geometry ............................................................................................................80 4.3 Assembly ............................................................................................................................84 4.4 VSWR and Far-Field Characterization .............................................................................85 ix