Folded Substrate-Integrated Waveguide Band-Pass Post Filter

This letter presents a novel concept of band-pass filter realized with metal posts in folded substrate-integrated waveguide (FSIW) technology, together with an efficient specific design procedure. As a first step, it is shown that a particular dimension of the middle vane in the FSIW yields an equivalence to a dielectric-loaded unfolded rectangular waveguide. This equivalence is investigated by comparing the modal dispersion characteristics in both folded and unfolded structures. A direct comparison of the posts placed in the FSIW and in the equivalent unfolded waveguide then further confirms their similar characteristics. As a result, the classical mode-matching method (MMM), straightforwardly applied in the equivalent unfolded structure, can be used to efficiently design a post filter in FSIW technology. For illustration, the method is applied to realize a 5th-order Chebyshev band-pass post FSIW filter with a center frequency of 7GHz and a fractional bandwidth of 5.71%. The viability and efficiency of the design approach is successfully validated by finite-element simulations and measurements.