Compact Quasi-Elliptic Wideband Bandpass Filter Using Cross-Coupled Multiple-Mode Resonator

A novel compact wideband bandpass filter (BPF) is proposed based on cross-coupled multiple-mode resonator (MMR). The proposed resonator is constructed by introducing cross coupling between the high-impedance lines of a classical MMR. It is shown that new symmetrical pairs of transmission zeros (TZs) can be generated at the lower and upper stopbands, respectively, leading to a quasi-elliptic function response that enhances the selectivity and out-of-band rejection significantly. One filter prototype is designed, fabricated and measured for validation and shows the expected performance.