Substrate Integrated Gap Waveguide Bandpass Filters with High Selectivity and Wide Stopband
In this paper, a seventh-order filter using substrate integrated gap waveguide (SIGW) technology, i.e. SIGW filter, is proposed for the first time, which has high selectivity and wide stopband. The SIGW filter includes three-layer substrates. The top layer substrate realizes a perfect magnetic conductor (PMC) using periodic plated vias and metallic patches. It is applied for packaging substrate integrated waveguide (SIW) filter to avoid interference and losses induced by external radiation emission and internal radiation leakage. The middle layer substrate generates a gap layer. In the base/bottom layer, cascaded resonators of the SIW filters are formed by properly etching slots on the metal plane and placing plated vias in the middle of this layer. The higher-order modes of TE103 and TE104 are suppressed using slots designed in the base layer at the third-order cavity, which leads to wide stopband. Moreover, the effect of the SIGW-based PMC structure on bandwidth and transmission zeroes is studied. The measured results demonstrate that the proposed SIGW filters perform well in the both passband and stopband.