Computer-aided design of circular ridged waveguide evanescent-mode bandpass filters using the FDTLM method

The analysis and design of a circular ridged waveguide evanescent mode bandpass filter are described. Two and three resonators filters are presented for the 30 GHz range. Insertion loss is typically below 1 dB and return loss is better than 20 dB, on the average. The full-wave FDTLM (frequency-domain transmission line matrix) method is used to compute the generalized S-parameters of the overall filter structures including the effect of finite metalization thickness and model interaction between filter discontinuities. A comparison to other filter structures in circular waveguides shows excellent agreement between measured and computed results.<>