Ultra‐compact highly selective quasi‐elliptic filters based on combining dual‐mode SIW and coplanar waveguides in a single cavity

Abstract

Two bandpass filters (BPFs) are implemented on a single dual-mode square-shaped substrate-integrated waveguide (SIW) cavity with two etched coplanar waveguides. The proposed BPFs can achieve two transmission zeros (TZs) using dual modes in the SIW cavity (i.e. TE₁₀₂ and TE₂₀₁) with non-resonating mode (i.e. fundamental TE₁₀₁), which provides a direct input-to-output coupling. Moreover, the positions of the two TZs can be tuned by changing the positions of input and output ports. Moreover, an extra TZ with controllable position is also achieved by using controllable electric and magnetic mixed coupling; and the TZ also can be split into two TZs for the mixed cross-coupling paths. The BPFs with the controllable TZs improve the selectivity and out-of-band rejection. The designed BPFs have a centre frequency of 5.8 GHz. The measured results agree with the simulated ones.