Dual passband filter based on semicircular cavity substrate integrated waveguide using complementary split ring resonators

This paper presents a compact dual passband filter based on semicircular cavity substrate integrated waveguide (SIW). Semicircular complementary split ring resonators (CSRRs) of unequal dimensions are loaded in the SIW to generate the passbands by lowering down the resonant frequencies below the cutoff frequency of the SIW. This loading of CSRRs provides independent control over the passband resonance frequencies by varying the ring dimensions. After introducing the CSRRs into the semicircular SIW cavity the proposed bandpass filter generates two passband resonances at 3.83 GHz and 7.36 GHz with 3 dB fractional bandwidth of nearly 34% and 10% respectively. Minimum insertion loss of less than 0.5 dB with a return loss better than 25 dB is realized for both passbands of the filter.