New dual-band band-pass filter design with enhanced dual-band skirt characteristics

A new frequency transformation concept is proposed to overcome the skirt characteristic of dual-band bandpass filters (BPF) caused by the conventional frequency transformation method. The new frequency transformation incorporates an extra frequency parameter to achieve additional rejection function in the high-frequency stop-band. To realize the concept, the dual-band BPF's resonators are modified based on their frequency responses. A new dual-band BPF was also designed with the modified resonators, fabricated and measured, and achieved desired enhanced skirt characteristic.