Characterization of semilumped CPW elements for Millimeter-wave filter design

In this paper, two accurate models for interdigital capacitors and shunt inductive stubs in coplanar-waveguide structures are presented and validated over the entire W-band frequency range. Using these models, a novel bandpass filter (BPF) and a miniaturized high-pass filter are designed and fabricated. By inserting interdigital capacitors in BPF resonators, an out-of-band transmission is introduced, which improves rejection level up to 17 dB over standard designs of similar filters. A high-pass filter is also designed, using semilumped-element models in order to miniaturize the filter structure. It is shown that a fifth-order high-pass filter can be built with a maximum dimension of less than λ_g/3. Great agreement between simulated and measured responses of these filters is demonstrated.