A compact dual-mode dual-band bandpass filter design with controllable first passband

A single patch resonator with right crossed slots and rectangular perturbation is proposed to implement a dual-mode dual-band bandpass filter. The first resonance varies with the width and length change of the slots leading to a flexibly tuned first passband during the design phase. The second resonance is not perturbed because of the right crossed slots. The rectangular perturbation located at the diagonal creates transmission zeros near the first passband edges while the spur-lines generate transmission zeros near the second passband so as to achieve higher frequency selectivity. Therefore the bandwidths of the two passbands can be tuned independently. A dual-mode dual-band filer operating at 1.57 and 5.2 GHz for GPS and WLAN application is designed and manufactured for demonstration. Good agreements are found between simulation and measurements.