Planar Realization of a Triple-Mode Bandpass Filter Using a Multilayer Configuration

A triple-mode bandpass filter has been designed using a multilayer approach. The filter topology consists of a square loop resonator located inside a resonant cavity. The walls of the cavity were designed using periodic metal vias that connect the top and bottom ground planes for an overall planar configuration. A filter prototype was fabricated and measured, producing a fully canonical filtering function with three resonant poles and three transmission zeros. The filter yielded an insertion loss of 1.1 dB at the passband centered at 5.8 GHz