A compact wideband bandpass filter (BPF) based on half-mode substrate integrated waveguide (HMSIW) is proposed in this paper. The proposed BPF is achieved by etching a couple of S-shaped complementary spiral resonators (S-CSRs) on the top layer of HMSIW cavity to achieve a wide passband as well as generate two transmission zeros in the vicinity of the passband respectively to improve the selectivity. In addition, compared with a conventional CSRs-loaded HMSIW structure, the proposed S-CSRs-loaded HMSIW makes the overall size of the filter largely reduced with the same electrical length. Among the HMSIW structures ever reported, the proposed S-CSRs are the first time to be introduced into HMSIW. To validate its practicability, a compact wideband HMSIW BPF loaded with S-SCRs has been designed and implemented through the PCB process. The measured and simulated S-parameters of the filter are presented to show the proposed filter's predicted performance, and good agreements is obtained between them. This result demonstrates that the newly proposed HMSIW structure loaded with S-CSRs is an excellent candidate for compact filters.
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