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Phase Center Stabilization of a Horn Antenna and Its Application in a Luneburg Lens Feed Array Written by Brian H Phase Center Stabilization of a Horn Antenna and its Application in a Luneburg Lens Feed Array by Brian H. Simakauskas B.S., University of Massachusetts, 2010 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfilment of the requirement for the degree of Master of Science Department of Electrical, Computer, and Energy Engineering 2015 This thesis entitled: Phase Center Stabilization of a Horn Antenna and its Application in a Luneburg Lens Feed Array written by Brian H. Simakauskas has been approved for the Department of Electrical, Computer, and Energy Engineering ______________________________________ Dejan S. Filipović ______________________________________ Maxim Ignatenko 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. iii Simakauskas, Brian H. (M.Sc., Electrical, Computer, and Energy Engineering) Phase Center Stabilization of a Horn Antenna and its Application in a Luneburg Lens Feed Array Thesis directed by Professor Dejan S. Filipović With any reflecting or refracting structure, such as a parabolic reflector or lens antenna, the knowledge of the focal point is critical in the design as it determines the point at which a feeding signal should originate for proper operation. Spherically symmetrical lenses have a distinct advantage over other structure types in that there exists an infinite number of focal points surrounding the lens. Due to this feature, a spherical lens can remain in a fixed position while a beam can be steered to any direction by movement of the feed only. Unlike phased arrays that beam-steer electronically, a spherical lens exhibits no beam deterioration at wide angles. The lens that accomplishes this is in practice called the Luneburg lens which has been studied since the 1940s. Due to the electromechanical properties of the horn antenna, it is often used to feed the above mentioned configurations. In the focusing of any feed antenna, its phase center is an approximate point in space that should be coincident with a reflector or lens’s focal point to minimize phase error over the radiating aperture. Although this is often easily accomplished over a narrow bandwidth, over wide bandwidths some antennas have phase centers that vary significantly, making their focusing a challenge. This thesis seeks to explain the problem with focusing a Luneburg lens with a canonical horn antenna and offers a modified horn design that remains nearly focused over a frequency band of 18 – 45 GHz. In addition to simulating the feed / lens configurations, the lens and feed horn will be fabricated and mounted for far field measurements to be taken in an anechoic antenna range. A final feed design will be implemented in an array configuration with the Luneburg lens, capable of transmitting and receiving multiple beams without requiring any moving parts or complex electronic beam-forming networks. As a tradeoff, a separate receiver or switching network is required to accommodate each feed antenna. This aspect of the system, however, is outside the scope of research for this thesis. iv Acknowledgements To the US Navy’s Office of Naval Research, I am extremely thankful for their support of this research and for my position with the Antenna Research Group. I know that I have taken a lot away from this experience and I hope my work will contribute to the long-term goals of the CIA project. I owe my advisor, Professor Dejan Filipović, a great deal of thanks for giving me the opportunity to work with the Antenna Research Group. During my tenure here, I not only gained invaluable experience and knowledge related to antennas and EM concepts, but through working with Filip and my peers I am privileged to have participated in an active research environment with such great people. Thanks to those who served on my thesis committee: Filip, Dr. Maxim Ignatenko, Dr. Neill Kefauver, and Dr. James Mead all who have provided much appreciated and useful feedback. Maxim’s guidance was extremely valuable throughout this entire project. I owe Dr. Nathan Jastram many thanks for his help with the antenna range in getting the measurements necessary for this thesis. I am also thankful to Jim, Ivan, and Andy of ProSensing. My experiences while working there are what motivated me to continue my education over three years ago. I owe my lovely fiancée Luella an enormous gratitude for her constant support throughout my graduate school career. From day one, she has not only tolerated my busy workload but has remained supportive and kept me motivated to see this through to the best of my abilities. I truly could not have asked for anyone better to share this experience with. Lastly, a thank you to my parents, brother, and sister for their unconditional support over all the years. v Contents Chapter 1 Introduction .................................................................................................................................. 1 1.1 Background ....................................................................................................................... 1 1.2 Luneburg Lens .................................................................................................................. 2 1.3 Horn Antennas .................................................................................................................. 4 1.4 Application ........................................................................................................................ 5 1.5 Phase Center Definition .................................................................................................... 6 Chapter 2 Extraction of Phase Center Position ........................................................................................... 10 2.1 Coordinate System / Geometry ....................................................................................... 10 2.2 Slope Method .................................................................................................................. 12 2.3 Least Mean Squares Solution .......................................................................................... 14 2.4 Exact Solution Using an Iterative Approach ................................................................... 16 2.5 Summary ......................................................................................................................... 18 Chapter 3 Phase Center of Horn Antennas ................................................................................................. 20 3.1 Introduction ..................................................................................................................... 20 3.2 Analytical Derivations .................................................................................................... 21 3.3 Example Horn Simulations ............................................................................................. 22 Chapter 4 Phase Stabilized Horn Design and Fabrication .......................................................................... 26 vi 4.1 Introduction ..................................................................................................................... 26 4.2 Methods for Phase Center Stabilization .......................................................................... 27 4.2.1 Flare Angle Design .................................................................................................... 27 4.2.2 Corrugations ............................................................................................................... 27 4.2.3 Flare Profile Design ................................................................................................... 30 4.3 Horn Design 1 ................................................................................................................. 32 4.3.1 Parametric Study Setup .............................................................................................. 32 4.3.2 Parametric Study Results ........................................................................................... 34 4.3.3 Fabrication ................................................................................................................. 36 4.3.4 Performance ............................................................................................................... 37 4.4 Horn Design 2 ................................................................................................................. 40 4.4.1 Parametric Study Results ........................................................................................... 41 4.4.2 Fabrication ................................................................................................................. 41 4.4.3 Performance ............................................................................................................... 43 4.5 Summary ......................................................................................................................... 45 Chapter 5 Luneburg Lens / Feed Horn Implementation ............................................................................. 47 5.1 Introduction ..................................................................................................................... 47 5.2 Luneburg Lens Simulation – Open-Ended Waveguide..................................................
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