New Techniques for Time-Reversal-Based Ultra-wideband Microwave Pulse Compression in Reverberant Cavities

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Virginia Tech


Generation of high-peak power, microwave ultra-short pulses (USPs) is desirable for ultra-wideband communications and remote sensing. A variety of microwave USP generators exist today, or are described in the literature, and have benefits and limitations depending on application. A new class of pulse compressors for generating USPs using electromagnetic time reversal (TR) techniques have been developed in the last decade, and are the topic of this dissertation. This dissertation presents a compact TR microwave pulse-compression cavity that has ultra-wide bandwidth (5 GHz – 18 GHz), and employs waveguide feeds for high-peak power output over the entire band. The system uses a time-reversal-based pulse compression scheme with one-bit processing (OBTR) to achieve high compression gain. Results from full-wave simulations are presented as well as measurements showing compression gain exceeding 21.2 dB, 22% efficiency, and measured instantaneous peak output powers reaching 39.2 kW. These are all record results for this type of pulse compressor. Additionally presented is new analysis of variation in compression gain due to impulse response recording time and bandwidth variation, new experimental work on the effect of mode stirrer position on compression gain, and a novel RF switch-based technique for reducing time-sidelobes while using OBTR. Finally, a new technique is presented that uses a reverberant cavity with only one feed connected to an ultra-wideband circulator (6.5 GHz to 17 GHz) to perform TRPC. Prior to this work, TRPC has only been demonstrated in electromagnetics using two or more feeds and a reverberant cavity acting as the time-reversal mirror. This new 1-port technique is demonstrated in both simulation and measurement. The proposed system achieves up to a measured 3 dB increase in compression gain and increased efficiency. Also, a novel application of the random coupling model (RCM) to calculate compression gain is presented. The cavity eigenfrequencies are modeled after eigenvalues of random matrices satisfying the Gaussian orthogonal ensembles (GOE) condition. Cavity transfer functions are generated using Monte Carlo simulations, and used to compute the compression gains for many different cavity realizations.



Ultra-short pulse (USP), pulse compression, ultra-wideband (UWB), time-reversal, reconfigurable cavity, dispersive cavity