Characterization and simulation of bi-quadratic coplanar waveguide tapers for time-domain applications

The design and performance of a novel coplanar waveguide (CPW) taper for picosecond pulse applications is described. Tapers with widely differing widths varying from 62.5 mu m to 900 mu m are investigated. The circuit characteristics were simulated in both time domain and frequency domain using a 3-D transmission-line-matrix (TLM) method. An optimum biquadratic shape which reduces the reflections from more than 5% to below 2% in comparison to a linear taper was found. The circuits were measured in the frequency range up to 40 GHz with a wafer prober. At 40 GHz, the insertion loss values were less than 0.4 dB. For a double taper, risetimes of 6.4 ps were achieved which correspond to a bandwidth of 55 GHz;.<>