Novel dual-mode resonator bandpass filter with high rejection in extended wide stopband

A dual-mode resonator filter is designed to have a wide upper stopband. The design incorporates a controllable transmission zero near the passband for selectivity enhancement. Through the proposed input and output coupling structure, more transmission zeros are generated for multi-order spurious passband suppression and upper stopband extension. As a result, the stopband is extended up to 7 times the center frequency (7f_o) with a rejection better than 30-dB, and to 5.82f_o with at least 40-dB. Measurement results show good agreement with simulation.