A Differential SISPSL Branch-Line Coupler With Common-Mode Suppression Using Compensated Stub

In this brief, a novel differential branch-line coupler based on substrate integrated suspended parallel strip Line (SISPSL) is proposed. The differential branch-line coupler is based on the multilayer structure, and utilizes the inherent differential characteristics of parallel strip line to construct the feeding port. The common-mode suppression is enhanced by loading a quarter-wavelength stub on the main transmission line at each port. The proposed SISPSL coupler is designed and fabricated using the PCB process, and it has the advantages of self-packaging and high common-mode suppression.