A compact sept‐band bandpass filter utilising a single multi‐mode resonator

This study proposes a compact sept‐band bandpass filter (BPF) with controllable centre frequencies and bandwidths. To achieve compact size and low insertion loss, the filter deploys a single multi‐mode resonator and abandons conventional source–resonator coupling structure to reduce the order of coupling sections. The fabricated BPF demonstrates seven passbands located at 1.0, 1.6, 2.3, 2.8, 3.5, 4.2, and 5 GHz, which are targeted for global system for mobile communications (GSM), wireless local area network, WIFI, and 4G/5G communication. Within the seven passbands, the minimum insertion losses are 0.9, 1.5, 0.5, 1.2, 0.9, 1.9, and 1.6 dB, respectively. The overall size of the fabricated filter is 0.1 λ g  × 0.21 λ g . This work provides a new approach to obtain the most passbands of BPF while achieving less insertion‐loss and enhanced selectivity simultaneously.