Design of a Multilayer Dual-Band Balanced Bandpass Filter on a Circular Patch Resonator

This letter presents a novel multilayer dual-band balanced bandpass filter (BPF) design by using two perturbed circular patch resonators. The TM 11 mode and 21 of the resonator with odd-symmetric field distributions are explored to realize desired differential-mode (DM) transmission common-mode (CM) suppression. Two patches properly coupled in back-to-back form dual-passband response virtue coupling apertures etched on ground. In addition internal coupling, above also further utilized for undesired degenerate harmonic Besides, slot perturbations introduced perturb resonant independently adjust center frequency higher passband, while lower passband remains almost unchanged. Thus, passbands can be flexibly controlled simultaneously tuning slots size patch. For validation, BPF prototype is implemented. results indicate 18 26% wide fractional bandwidths centered at 5.5 7.5 GHz return loss than 20 dB under DM operation CM suppression 40 over an ultra-wide band.