A Novel Compact Tri-band Filter Based on a Single Substrate Integrated Waveguide Cavity

A compact tri-band bandpass filter (BPF) using a single substrate integrated waveguide (SIW) cavity with offset feed-line is proposed in this paper. Firstly, a single SIW cavity fed by microstrip-line and L-shape slots with rectangular slot is applied to construct a tri-band BPF. The offset feed-line is used to excite the three resonant modes to achieve the three passbands. The rectangular slot in the SIW is applied to improve the filtering performance. This filter has a very compact configuration, which still remains a good filtering performance. Then, a second order tri-band filter based on the first order tri-band filter is designed and analyzed. Finally, the proposed second order tri-band filter is fabricated and verified by simulations and experiments.