Analysis of 220-GHz Low-Loss Quasi-Elliptic Waveguide Bandpass Filter

A 220-GHz low-loss and wideband waveguide bandpass filter with fourth-order quasi-elliptic response is presented and analyzed in this letter. An electric cross-coupling realized by easily manufactured capacitive iris is introduced in the classical folded quadruplet topology. The prototype fabricated by conventional computer numerical control (CNC)-metal-milling technology exhibits meaningful results of an insertion loss of around 0.6 dB and a 3-dB fractional bandwidth of 9.8% centered at 214.3 GHz, which are in excellent agreement with the simulated ones. The effects of tolerance and surface roughness on the filter performance are discussed in detail. All the results indicate that the present CNC process can meet the accuracy and roughness requirement of such waveguide filter in WR-4 band.