Two Compact Bandpass Filters With Controllable Band Based on Eighth-Mode Substrate Integrated Waveguide

In this brief, the hybrid technique of eighth-mode substrate integrated waveguide (EMSIW), coplanar waveguide (CPW) resonator, and complementary split-ring resonator (CSRR) is studied. On this basis, two compact bandpass filters (BPFs) with a controllable band based on EMSIW are proposed in this brief. Filter I embeds a CPW resonator between two cascaded EMSIW resonators, increasing the coupling of the two cavities without increasing the circuit size. Filter II is loaded with CSRRs between each of the EMSIW cavities. The fundamental mode of the SIW cavity and CSRR mode generates two separate passbands that can be independently controlled. The coupling topology and working principle of the two filters are illustrated through eigenmode simulation, field distribution analysis, and equivalent circuit model analysis. Compared with the reported works, both filters have compact size (
$0.33\,\,\lambda _{\mathrm{ g}} \times 0.33\,\,\lambda _{\mathrm{ g}}$
), and high slope selectivity in addition to a tunable passband.