Ultra-wideband characterization of lossy materials: short-pulse microwave measurements

Planar antennas are switched photoconductively to generate picosecond bursts of freely propagating radiation with usable spectral amplitudes in the 5-to-86-GHz frequency range. This radiation is used to measure the frequency-dependent, complex index of refraction of dispersive materials in reflection and transmission. Novel deconvolution techniques are also demonstrated for extracting frequency-domain information from time-domain measurements. Experimental results are presented for the particular case of water, and the relative merits of reflection and transmission time-domain measurements on materials are discussed. It is shown that the frequency-domain results from transmission measurements are generally of better accuracy than reflection measurements, although reflection measurements are required for thick lossy samples. Good results were obtained over a significantly wider bandwidth in transmission than were obtained in reflection.