Accurate design of pseudoelliptic inline SIW filters with frequency-dependent couplings

This paper presents an accurate synthesis method for inline SIW (Substrate Integrated Waveguide) generalized Chebyshev bandpass filters with frequency-dependent couplings. The technique is based on the synthesis of a coupling matrix that takes into account the impedance of the frequency-dependent stub. Thus, a loading effect compensation in adjacent resonators (via resonant frequency adjustment) and coupling elements (via coupling-value modifications) is possible. The application of this method of synthesis is illustrated through an experiment in which a third-order filter consisting of rectangular half-wavelength resonators is implemented in substrate integrated waveguide (SIW) technology. The resonators are separated by inductive irises and a parallel shorted stub. The stub acts as a dispersive inverter and produces the transmission zero. A substantial improvement in design accuracy is thus obtained. The measured and simulated results for this method are in good agreement.