Miniaturised high-isolation K-/Ka-band diplexer with 3D antarafacial channel integration using vertical quasi-coaxial matching network

A miniaturised high-isolation K-/Ka-band diplexer with exceeding adjacent channels using 3D antarafacial channel integration and vertical-quasi-coaxial-based matching network is proposed. For smaller size, lower loss and lower channel interference, the high-order low-pass filter for the K-band channel and the four-line-interdigital-coupled wideband bandpass filter for the Ka-band channel are respectively designed on two low-loss glass-based substrates, and these two substrates are integrated on the two antarafacial surface of the mounting board. The vertical-quasi-coaxial (VQC) embedded in the mounting board is not only used as three-dimensional (3D) interconnection of the two antarafacial channels but also designed as the constituent part of the matching/isolation network, and this can effectively decrease the impedance traction caused by the Ka-band filter for the K-band channel of the diplexer. In addition, four transmission zeros of the K-band filter are designed at the whole passband of the Ka-band channel to improve the isolation to the K-band channel for guaranteeing the performance of the diplexer at the Ka-band channel. Furthermore, working principle, design method and test solution of this proposed K-/Ka-band diplexer are well illustrated, and the high-isolation (>40 dB) in very adjacent wideband channels at K-band (18-23.5 GHz) and Ka-band (25.8-31.6 GHz) is achieved within a tiny size of 9 x 4 x 0.87 mm.