Compact-Balanced BPF and Filtering Crossover With Intrinsic Common-Mode Suppression Using Single-Layered SIW Cavity

In this letter, compact-balanced bandpass filter (BPF) and filtering crossover are proposed with intrinsic common-mode (CM) suppression by using a single-layered substrate-integrated waveguide (SIW) cavity. The SIW cavity with low profile is TEn0m mode resonator, which has only one nonzero electric field component. Hence, it is also a natural frequency selection device of the differential signal. Meanwhile, the CM signal cannot excite the cavity due to the characteristics of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). For the design of the balanced SIW BPF, the differential-mode (DM) equivalent half circuit is a single-ended SIW filter with height halved. Furthermore, the microstrip differential transition structure is designed to excite the SIW cavity and has little conversion between DM and CM. On this basis, a compact SIW-balanced filtering crossover is proposed using the degenerate modes TE
₁₀₂
and TE
₂₀₁
. Finally, compact third-order SIW-balanced BPF and filtering crossover are designed and fabricated, and the measured results show good agreement with the simulated ones.