Substrate-Integrated Waveguide Triple-Band Bandpass Filters Using Triple-Mode Cavities

Substrate-integrated waveguide (SIW) triple-mode triple-band bandpass filters (BPFs) are synthesized, designed, and demonstrated for the first time based on a novel type of SIW triple-mode square cavities perturbed by centered cross-shaped metallized via holes. The resonant characteristics of the cavity are analyzed first to show the range of the realizable frequency ratios, and the design parameters corresponding to the specifications, i.e., the external quality factors and the internal coupling coefficients for the three passbands, can be specified flexibly within certain ranges by exploiting an advanced triple-mode coupling controlling technique. Two SIW triple-mode triple-band BPFs, including a third-order direct-coupled one operating at 13, 14, and 15 GHz and a fourth-order cross-coupled one operating at 11, 12, and 13 GHz, are synthesized, designed, fabricated, and measured for demonstration. Compact circuit sizes and excellent filtering performances have been achieved for the two prototypes.