Compact wide-stopband SIW dual-band filter with closely spaced passbands

Abstract

Compact substrate-integrated waveguide (SIW) dual-band bandpass filter with closely spaced passbands and wide-stopband characteristics is proposed for the first time based on inline-coupled perturbed SIW triple-mode cavities. The first three resonant modes in the triple-mode cavities can be flexibly controlled so that two closely spaced passbands can be realised based on the first two resonant modes, and wide-stopband can be achieved by staggering the third and other higher-order resonant modes without resorting to extra structures. The external and internal couplings of the dual passbands can be specified and designed flexibly benefitting from the offset feeding ports and coupling windows. A prototype centred at 13 and 14 GHz is synthesised, designed, fabricated, and tested as a demonstration, extending the stopband to 1.97f1 with rejection level better than 25 dB.