Pseudo-elliptic substrate integrated waveguide filters with higher-order mode resonances

Two substrate integrated waveguide (SIW) pseudo-elliptic bandpass filters are presented that utilize higher-order mode cavities. In the first filter, two full-wave TE₁₀₂ resonators and two fundamental TE₁₀₁ resonators in a compact structure are properly coupled to generate two transmission zeros in a four-pole SIW filter. The coupling matrix of the structure with a centre frequency of 10 GHz and 200 MHz bandwidth is designed, and good agreement is achieved with simulations of two commercially available field solvers. In the second topology, by using symmetric inductive discontinuities and two rectangular SIW cavities, TE₁₀₂ and TE₃₀₁ modes are excited and generate two transmission zeros, one on each side of the passband. This dual-mode SIW filter with a centre frequency of 10 GHz and bandwidth of 300 MHz has been prototyped, and the measured data are in good agreement with results obtained from the coupling matrix and CST Microwave Studio.