Miniaturized Diplexer Using Dual Half-Mode SIW Cavity for 5G Sub-6 GHz Communications

Prof. Mojgan Daneshmand made seminal contributions to the advancements of substrate integrated waveguide (SIW) technology together with her students and colleagues. In this paper, we present our recent work on miniaturized SIW diplexer in memory of Mojgan and her family. The proposed diplexer is centered at 3.45 and 4.9 GHz for 5G sub-6 GHz communications, which is enabled by a common dual half-mode substrate integrated rectangular cavity (HMSIRC) coupled with singlemode cavities in each channel. Besides the elimination of T-junction, HMSIRCs are also introduced for the miniaturization of sub-6 GHz circuits. Additionally, by employing the first two modes in the dual-HMSIRC, a large frequency ratio of 1.42 between 3.45 and 4.9 GHz can be realized, which is difficult to implement with the original whole cavity scheme because of spurious passband problems. A 2^nd-order example with ripple fractional bandwidths of 2% and 1.6% for the two channels is synthesized, designed, fabricated, and tested for demonstration.