Design of Filtering Magic-T with Wideband and Wide Stopband Based on HMSIW and Spoof Surface Plasmon Polaritons

A novel filtering magic-T (FMT) with a compact size, a broad bandwidth, and a wide stopband rejection based on the dielectric-covered L-shaped groove (DCLSG) half-mode substrate integrated waveguide and the spoof surface plasmon polariton (HMSIW-SSPP) structure is proposed for the first time. A HMSIW magic-T (HMT) based on dual-layer substrates is first designed. Then, we construct the proposed FMT by periodically etching the subwavelength DCLSG SSPP structure into the HMT. The proposed FMT achieves a bandpass filtering response and a nearly 50% reduction of longitudinal dimension attributed to the bandpass characteristics and strong slow-wave property of the DCLSG HMSIW-SSPP structure. In addition, beneficial from the regulable cut-off frequencies of the DCLSG HMSIW-SSPP structure, the proposed FMT provides a wide impedance bandwidth and independently adjustable lower and upper cut-off frequencies of the passband. Finally, a prototype of the proposed FMT is fabricated to validate this design idea. The measured results illustrate that the FMT has a 3-dB fractional bandwidth of 40.23% and a 20-dB stopband rejection up to 2.12 f₀ (f₀: center frequency of the passband).