High-selectivity dual-passband bandpass filter with dual coupled lines

A microstrip dual-band bandpass filter is presented. By adjusting the even- and odd-mode impedances, two resonances formed two passbands. Moreover, transmission zeros are located at both sides of two passband skirts, which can be adjusted by the coupling coefficient of the shorted coupled line. For demonstration, a dual-band bandpass filter operating at 0.8 and 2.2 GHz is designed and fabricated. The theoretical analysis and measurement are presented. Good agreement verifies the proposed method.