In this letter, compact ultra-wideband filters are designed by employing a novel ridged half-mode folded substrate-integrated waveguide (RHMFSIW) and double-ridged half-mode SIW (DRHMSIW). The RHMFSIW is proposed by loading the half-mode folded substrate integrated waveguide with a ridge, where the ridge introduces additional capacitance hence leading to a lower cutoff frequency and a smaller size. Compact ultra-wideband filters are designed and fabricated based on the RHMFSIW. Another novel DRHMSIW is developed to implement the tight coupling required in the ultra-wideband filters. To improve...
