Compact Wideband Ridge Half-Mode Substrate Integrated Waveguide Filters

In this paper, the propagation properties of the ridge half-mode substrate integrated waveguide (RHMSIW) are analyzed and RHMSIW coupling topologies to implement compact wideband filters are explored. The propagation constant and the cutoff frequency of the RHMSIW are discussed. Two types of ultra-wideband RHMSIW coupling topologies are proposed by employing the evanescent-mode HMSIW and RHMSIW structures. To improve the stopband performance while keeping a small size, another novel mixed-coupled RHMSIW topology is developed to introduce transmission zeros in filters by combining the evanescent-mode coupling with the slot coupling. Wideband RHMSIW filters are designed and fabricated with these coupling topologies. It is shown that compact size and good stopband performance can be achieved for the proposed wideband RHMSIW filters.