Resonance Characteristics of Substrate-Integrated Rectangular Cavity and Their Applications to Dual-Band and Wide-Stopband Bandpass Filters Design

Resonance characteristics of substrate-integrated rectangular cavity (SIRC) are systematically analyzed in this paper. Synthesis design techniques of substrate-integrated waveguide (SIW) dual-band bandpass filters (BPFs) and wide stopband BPFs are demonstrated on the basis of these characteristics. The design concept of dual-band BPFs is to add some extra single-mode SIRC resonators to dual-mode resonator filters to increase the degrees of freedom in extracting direct-coupling coefficients, while the external quality factors Qe and crosscoupling coefficients desired in two passbands can be realized simultaneously by determining proper offset position of the I/O ports and cross-coupling window, respectively. Consequently, all the design parameters including Qe and coupling coefficients Mi j required for both the passbands could be satisfied. The principle of wide-stopband BPFs is to select the constitutive SIRC resonators with identical fundamental frequency but staggered higher order ones to suppress multispurious peaks to low levels and narrow bandwidths. Then emphasis is placed on the rejection of TE202 mode, with its resonant frequency two times of TE101 for all SIRC resonators, by centered I/O ports and coupling windows. Several experimental prototypes of SIW dual-band BPFs and wide-stopband BPFs are designed and fabricated to validate these concepts. The measured results are in excellent agreement with the simulations.