WR-4 Band Wideband Waveguide Diplexer Based on Spoof Surface Plasmon Polaritons and Its Application in Terahertz Communications

In this article, a wideband diplexer is proposed based on spoof surface plasmon polaritons (SSPPs). The dispersion properties of the SSPP unit cell are analyzed, which shows that the upper/lower cutoff frequency and the bandwidth of the channel filter can be flexibly controlled. Based on the proposed SSPP-based bandpass filter (BPF), a WR-4 band wideband diplexer is further developed by the space-mapping technique, which is used to achieve high computational efficiency and design accuracy. For demonstration, two SSPP-based channel BPFs and the proposed diplexer are fabricated by high-precision computer numerical control (CNC) milling technology. The measured results show that the average insertion losses (ILs) of two BPFs are 1.6 and 2.4 dB, respectively, and the return losses are both better than 17 dB. Meanwhile, the measured 3-dB bandwidth of the proposed diplexer is 174–204 GHz and 225–255 GHz for two channels. The average ILs are 1.8 and 2.7 dB within the passbands of two channels, and the corresponding return losses are both better than 16 dB, which are all in good agreement with the simulated ones. Furthermore, a WR-4 band dual-carrier wireless link is built based on the proposed diplexer for future 6G terahertz (THz) communications. The corresponding real-time date rate is 41.6 Gbps for the proposed wireless link and the transmission distance is up to 3 km.