Miniaturized SIW filter using D-shaped resonators with wide out-of-band rejection for 5G applications

In this article, substrate integrated waveguide (SIW) filter with compact size and wide out-of-band rejection is designed for 5G (sub-6 GHz) applications. To achieve the proposed filter responses, D-shaped resonators oriented face-to-face are etched out on the top layer of SIW. Due to the resonators loading, the filter provides a passband below the cut-off frequency of SIW. This decrease in the operating frequency of the filter allows us to achieve size miniaturization. To enhance the frequency responses, a double-stage SIW filter is proposed and investigated. The equivalent electrical-circuits are developed to validate the transmission responses. To support our claim, single- and double-stage SIW filters are designed, fabricated and tested. The filter prototypes achieve size miniaturization, low insertion loss and wide out-of-band responses. The measured responses are very similar to the full-wave simulation responses.