Duplexer Based on Spoof Surface Plasmon Polaritons Transmission Lines

We propose duplexer based on spoof surface plasmon polaritons (SSPPs) transmission lines (TLs). The duplexer consists of two domino SSPP TLs with different lower cut-off and higher cut-off (asymptotic) frequencies, forming the two frequency band channels. The low frequency band channel is the domino SSPP TL with higher unit height. For the branch of the high frequency band channel, which is based on a SSPP TL with lower unit height, multiple SSPP TL sections functioning as band-stop structures are placed aside the SSPP TL to realize satisfying out-of-band rejection below the lower cut-off frequency. The two branches are fed through a common rectangular waveguide. Different transition length of the two branches as well as a shifted placement from the center is designed to achieve efficient transition for both branches at respective bands.