Experimental Investigation of UWB Impulse Response and Time Reversal Technique Up to 12 GHz: Omnidirectional and Directional Antennas

An experimental study of the time reversal (TR) technique is presented in a single-input-single-output configuration over the frequency range of 2-12 GHz. A special emphasis of this work is to investigate and compare impulse response (IR) and TR characteristics for omnidirectional biconical and directional spiral antennas over realistic indoor ultrawideband (UWB) channels in both line-of-sight (LOS) and non-line-of-sight (NLOS) environments. We discuss the effects of channel multipath dispersion and antenna frequency-dependant delay distortions on the received responses in both time and frequency domains. The effectiveness of TR for waveform compression is characterized by computing root mean square delay spread and peak-to-average power ratio. Our study suggests that the effectiveness of time reversal is subject to a tradeoff between competing effects-namely, compensation of spectral phase variation (which leads to compression) and aggravation of spectral amplitude structure (which opposes compression). Although TR is a powerful technique for compensation of phase distortions associated with broadband frequency-independent antennas (as shown in LOS experiments with spiral antennas), it shows only modest performance in compressing time spread associated with multipath delays.