Short-pulse propagation in a hollow waveguide: analysis, optoelectronic measurement, and signal processing

An asymptotic analysis is performed for short-pulse propagation in a hollow waveguide. It is demonstrated that each time-domain mode supported by the guide is characterized by a time-dependent frequency which, as time proceeds, approaches the modal cutoff frequency. This phenomenon is demonstrated experimentally by performing short-pulse optoelectronic measurements for the case of rectangular waveguide. In these measurements a short-pulse laser is used to switch planar antennas photoconductively, generating freely propagating waveforms with instantaneous bandwidth from 15-75 GHz. Time-frequency signal processing is performed on the measured data, the results of which are in close agreement with the predictions of the asymptotic analysis