Compact single- and dual-band band-pass filters employing mixed eighth-mode substrate-integrated waveguide and microstrip line resonators

In this study, single- and dual-band band-pass filters (BPFs) employing mixed eighth-mode substrate-integrated waveguide (EMSIW) and microstrip line (MSL) resonators are proposed and investigated. The mixed resonators feature compact circuit size, moderate quality factor and flexible design topology. By exploiting the mixed resonators to implement the BPF designs, a single-band BPF is developed, exhibiting four-order broadband band-pass filtering responses in a single-layered substrate. Several transmission zeros are introduced near the working passband to enhance the frequency selectivity. Moreover, the proposed BPF has the capability to suppress the harmonics superior to 20 dB rejection level up to 2.36 f(0). Meanwhile, two dual-band BPFs are designed in double-layered substrates with magnetic and electric coupling schemes. Both dual-band BPFs exhibit compact circuit size and low insertion loss. To the best of the authors' knowledge, it is the first time to develop single- and dual-band BPFs based on mixed EMSIW and MSL resonators in this study. For demonstration, a series of single- and dual-band BPFs with mixed SIW/MSL resonators are developed and fabricated. The simulated, measured and synthesised results have reached satisfactory agreements.