Numerical and experimental evaluation of sinuous antennas for remote sensing applications

Abstract

The objective of the research presented in this dissertation is to analyze the operation of the sinuous antenna and seek to overcome practical design challenges when utilizing the antenna in radar applications. The sinuous antenna can operate over ultra-wide bandwidths while producing polarization diversity, which makes the antenna an attractive candidate for polarimetric radar. However, the sinuous antenna may suffer from unintended resonant modes which distort the radiation and will produce ringing when the antenna is used to transmit pulses. An investigation was performed to determine the correlation between design parameters and these resonant modes. Design guidance is presented, which mitigates the excitation of these modes. A new sinuous antenna outer truncation technique is also presented, which prevents low-frequency resonances. Dispersion in sinuous antennas is another undesirable characteristic when radiating pulses.Since the active region on the antenna moves with frequency, the spectral content of the radiation is spread out over time. The original pulse may be reconstructed by applying a phase correction that compensates the dispersive effects. A simple dispersion model that is suitable for a fieldable system is proposed and implemented, which allows the antenna to transmit and receive temporally short pulses successfully. With these design challenges overcome, a new sinuous antenna was developed for the detection of targets close to the ground surface with ground-penetrating radar (GPR). GPR systems often employ a bistatic antenna configuration; however, this leads to extreme bistatic angles when attempting to detect targets close to the ground surface, which often reduces system performance. The operation of the sinuous antenna as an array of closely spaced yet independent arms is investigated as a potential quasi-monostatic antenna with a low height profile. The quasi-monostatic configuration dramatically reduces the bistatic angles, which significantly improves performance for close-in targets while keeping the isolation to a manageable level. A prototype antenna is fabricated and integrated into a GPR testbed. The polarimetric nature of the antenna allows for the discrimination between linear and circular targets, which is demonstrated with measured data.