A New Design Approach for Balanced Bandpass Filters on Right-Angled Isosceles Triangular Patch Resonator

A new approach to design a balanced bandpass filter (BPF) is presented in this letter. By virtue of resonant properties of a right-angled isosceles triangular patch resonator (RAITPR), a modified RAITPR with one electric wall and two magnetic walls is constructed. This resonator, namely, half-mode RAITPR, can support half-TM10-mode of the RAITPR. By adopting proper coupling topology between three adjacent RAITPRs and two half-mode RAITPRs, a third-order balanced BPF is proposed to achieve good differential-mode filtering selectivity and high common-mode suppression. To verify this design concept, a balanced BPF operating at 2.0 GHz with a 3-dB fractional bandwidth of 12.9% is in final designed and fabricated. Good agreement is achieved between the simulated and measured results over a wide bandwidth from 0 to 4.0 GHz.