Date of Award

8-2017

Document Type

Thesis - Open Access

Degree Name

Master of Science in Electrical & Computer Engineering

Department

Electrical, Computer, Software, and Systems Engineering

Committee Chair

Dr. William C. Barott

First Committee Member

Dr. Brian Butka

Second Committee Member

Dr. Thomas Yang

Abstract

The radio spectrum is becoming increasingly crowded. Researchers are putting efforts into finding ways to increase spectrum utilization. The National Science Foundation (NSF) is funding research to study various methods to improve utilization of the spectrum and reduce the influence of interference. In the Radar & Microwaves Laboratory at Embry-Riddle, research is being conducted for the applications of passive radar and radio astronomy. As interference is a major threat to both of these applications, interference mitigation is a requirement. More commonly, antenna arrays are used for research in both applications as they can improve performance and reduce cost.

The focus of this thesis is the development of a prototype testbed for real-time experimental studies of time-modulated arrays (TMAs). The design includes in-lab development of antenna elements, systems development of the heterodyne receiver architecture, and development of firmware and software for receiving and analyzing RF signals. The TMA antennas and radios are designed to operate at about 2.3 GHz. This targets passive radar using XM Radio as the transmitter of opportunity. The prototype testbed is designed to show the capabilities of multibeaming and interference suppression using time-modulated arrays.

To verify the performance of the system, each subsystem underwent specific testing. Once all subsystems are verified, the entire system underwent various experiments to show the capabilities. These experiments included bench-top receiver verification, Vector Network Analyzer (VNA) verification of array elements, and over the air experimentation to show the harmonics of element switching during operation. In addition to the hardware, simulations show the effects that design has on the system. The simulations explore the effects of time-modulation and optimization of element weights. A new method of optimization was experimented with. The method is an iterative convex optimization process that begins with an ideal system with a known solution. The problem is then morphed into the actual system, which has a more complex solution, through an iterative process. At each step, the system is optimized through the use of a hill climbing algorithm and the new values become the initial values for the next step. This iterative process is used to improve the optimization than applying a single hill climb optimization on the complex system with an unknown solution. The simulations show that the element spacing is a major factor in performance of the system.

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