A Substrate Integrated Waveguide (SIW) Bandpass Filter in A Box Configuration With Frequency-Dependent Coupling

This letter presents the design of a microwave bandpass filter with frequency-dependent coupling implemented in substrate integrated waveguide (SIW) technology. The proposed filter implements a four-pole generalized Chebyshev filtering function with two transmission zeros. Resonators are arranged in an extended box configuration with dispersive coupling on a main signal path, which produces an extra zero in comparison to classical approaches. The frequency-dependent coupling is implemented as a shorted stub with an additional septum made from via-holes. Such modification allows better control of the positions of the resonant frequencies of coupled SIW cavities, as well as of the position of the transmission zero. The filter was fabricated in SIW technology and good agreement was achieved between the simulated results and those measured.