Wide‐stopband substrate‐integrated waveguide diplexers and dual‐band bandpass filter with large frequency ratios

Abstract

Compact substrate-integrated waveguide (SIW) diplexers and dual-band bandpass filter (BPF) with widely separated passbands and wide-stopband are proposed for the first time based on half-mode substrate-integrated rectangular cavity (HMSIRC). Thanks to the dual-mode cavities and two respective channels, the frequencies and couplings of the two passbands can be flexibly controlled. To conquer the limitation of conventional full-mode cavity, the use of HMSIRC could intrinsically reject TE201 mode and many higher-order even modes, simultaneously realizing wide-stopband and widely separated passbands based on TE101 and TE102 modes. Moreover, the properly arranged internal coupling windows, which could intrinsically suppress the specific unwanted modes by sufficiently employing the existing design degrees of freedom, help further separate the two passbands and extend the stopband. The passband and stopband responses are systematically analyzed for different frequency ratios with the realizable frequency ratio and stopband bandwidth up to 1.91 and 2.65f1, respectively, which supplies the design guideline for SIW diplexers and dual-band BPFs with widely separated passbands and wide-stopband. Two SIW diplexers and an SIW dual-band BPF with frequency ratios of 1.72, 1.85, and 1.72 are synthesized and designed for demonstration, realizing the rejection levels and stopband bandwidths of 20 dB/2.34f1, 35 dB/2.36f1, and 20 dB/2.6f1, respectively.