Miniaturized half-mode substrate integrated waveguide bandpass filters using cross-shaped fractals

This paper presents a novel miniaturization technique for half-mode substrate integrated waveguide (HMSIW) bandpass filters using cross-shaped fractal structures. The overall filter area is reduced by 28% and 37% compared to conventional HMSIW bandpass filters when the first and second iterations of the cross-shaped fractals are used, respectively. In addition, the miniaturized filters exhibit lower insertion losses because the measured resonator unloaded quality factor increases from 221 for a conventional HMSIW resonator, to 258 and 264 for the first and second fractal iterations, respectively. To make the filter compact, a novel capacitive coupling mechanism is introduced in this work that results in improved upper stopband rejection due to a transmission zero above the filter passband. Two-pole, 4.5% Chebyshev bandpass filter prototypes with center frequency of 1.15 GHz are designed and fabricated on Rogers RT/Duroid 6010LM substrate. The filters have measured insertion losses <;1 dB and return losses better than 11 dB, and are very suitable for compact wireless communication systems.