In this paper a substrate integrated waveguide (SIW) quasi-elliptic filter with a controllable bandwidth is proposed. The quasi-elliptic filter response is caused by the cross coupling technique and a dual-mode resonance cavity. The dual-mode resonance cavity with TE 101 and TE 102 modes is used to generate the passband, and the cross coupling provides two signal transmission paths to produce transmission zeros (TZs). The bandwidth of the filter can be controlled by a pair of disturbing metallic via-holes. A quasi-elliptic filter with the center frequency of 11.03 GHz is designed, fabricated and measured. The experiment data agree well with the simulated ones.

Abstract-A new class of tri-band bandpass filter(BPF) is presented, and harmonic passband bandwidth can be independently controlled. In the implementation, three coupling paths are used to control the bandwidth of each passband. The first coupling path is two grounded vias which are utilized to realize coupling between two short-stub loaded resonators. And the first coupling path delivers signals at the first passband. Meanwhile, the second coupling path delivers signals at both the first and second passbands. And the third coupling path only delivers signals at the third passband. Using this method, both the frequency and bandwidth of each passband can be designed and tuned easily. In this filter design, the first harmonic passband can be adjusted separately and is independent of the fundamental passband. Two grounded vias improve flexibility and form a fundamental passband and harmonic passband independently controllable passband filter. For demonstration, a tri-band BPF with three passbands at 1.5 GHz, 2.5 GHz, and 3.5 GHz with insertion losses of 0.34, 0.76 and 1.08 dB is designed, fabricated and measured. So this proposed filter will be attractive in wireless communication systems.