Ultra-Wideband Pulse Shaping Using Lossy and Dispersive Nonuniform Transmission Lines

This paper presents the first known synthesis method for the design of nonuniform transmission lines (NUTLs) for ultra-wideband (UWB) pulse shaping, which can account for, and partially compensate for, the loss and dispersion present in real transmission lines. Without this compensation, cumulatively increasing distortion occurs in UWB pulse trains generated using NUTLs. The synthesis method novelly combines techniques from both the microwave and digital design domains: first, the transfer function of the transmission line is modeled as a cascade of minimum-phase and all-pass networks in the Z-domain; next, this model is used in a modified layer-peeling algorithm that automatically partially corrects for line nonidealities. Two possible implementations are presented: one taking advantage of noncausal filtering and the other with filtering implemented in the frequency domain. The effectiveness of the method is confirmed with both simulations and measurements of an UWB pulse shaper, which generates the first known sequence of modified Hermite polynomial pulses with successful compensation for loss and dispersion in an NUTL up to 15 GHz. The presented example shows that the synthesis method reduced the error between NUTL models and measurements by an average of 55%.