Design of dual-mode band-pass filter employing dumbbell-shape resonator

A novel band-pass filter using a dual-mode resonator is presented with a excellent performance. The effect of out/input coupling structures arranged at 1800 geometrically is discussed for the dual-mode filter. The coupling coefficient between degenerate modes of dual-mode resonator is investigated by the perturbation size. The dual-mode band-pass filter is designed, fabricated and measured. The filter is designed and implemented at 2.8 GHz with 10.5% bandwidth, and the performances show a low passband insertion loss of 0.7 dB with good harmonics inhibited and the rejection better than 25 dB from about 3 GHz.