High common-mode suppression balanced bandpass filter using isosceles right-angled triangular resonator

A balanced bandpass filter with high common-mode (CM) suppression using isosceles right-angled triangular (RAT) resonator is proposed in this Letter. The two high order orthogonal modes (TM210Z and TM200Z) are generated in the two overlapped isosceles RAT resonators under differential-mode (DM) and CM excitation, respectively. In this structure, TM210Z mode will be transmitted and TM200Z mode will be blocked. Furthermore, four via-holes are introduced to disturb TM210Z mode while TM200Z mode is unaffected, in order to shift the DM passband to the position of CM suppression. The designed balanced bandpass filter operating at 6.12 GHz with 3 dB fractional bandwidth of 5% is fabricated and measured. The measured and simulated results match very well with each other validating the feasibility of the proposed design concept.