Reduction of insertion loss in millimeter-wave tunable filter over 100 GHz

Rapid advances in millimeter-wave wireless communication technologies require accurate spectrum analysis in the frequency domain over 100 GHz. A tunable pre-selection filter is a key device in building such a spectrum analyzer. We have prototyped a new tunable filter in the frequency range from 110 to 140 GHz, but it suffered significant insertion losses around 116 and 140 GHz. This paper clarifies structural causes of these losses and presents the correct dimensions of the filter. Computer simulation of the redesigned filter gives reduced and flattened insertion loss in the working range.