Compact, dual-band, and hybrid filter based on combline and substrate integrated waveguide resonators

A novel compact hybrid dual-band bandpass filter based on combline and substrate integrated waveguide (SIW) resonators is proposed. By exploring an SIW-based hybrid cavity structure, a controllable dual-band response is achieved. The low-frequency passband is obtained by the combline, or mushroom resonators and the high-frequency passband is formed by the TE101 and TE301 modes. Unlike other designs that use the main mode and the high-order mode of the same resonator, we innovative use the TE301 mode of the rectangular cavity and cleverly divide this rectangular cavity into two small cavities, and use its TE101 mode to form the second passband with the TE301 mode of the large cavity. To improve the selectivity and out-of-band suppression, three transmission zeros are configured in this design. In order to verify the proposed design concept, a compact dual-band filter using this hybrid resonance structure is fabricated and measured. It demonstrates good filtering performance, including a compact size of 0.45 x 1.09 lambda(0), a low insertion loss of 0.57 and 1.67 dB in the two bands, and a high-design flexibility.