Balanced-to-Balanced Diplexer and Quadruplexer With High Selectivity and Wide CM Suppression

Abstract

In this brief, a balanced-to-balanced diplexer with high selectivity and wide common-mode (CM) suppression is presented and analyzed. Based on the proposed diplexer, an improved quadruplexer is designed. The balanced diplexer and quadruplexer are based on U-type microstrip feedlines, stepped-impedance microstrip/slotline transition structures and bandpass filter units. The design of U-type microstrip feedline and slotline transition is adopted at input and output ports, therefore the differential-mode (DM) response and intrinsic broad bandwidth CM suppression can be realized. By employing two or four stub-loaded resonators (SLRs), two or four channels with different frequencies can be achieved, respectively. Meanwhile, the center frequencies, fractional bandwidth (FBW) and transmission zeros (TZs) can be controlled by changing the dimensions of SLRs. The presented diplexer and quadruplexer exhibit sharp out-of-band rejection. To the author's knowledge, this is the first article to propose a balanced quadruplexer. In order to verify the feasibility of proposed design, a diplexer and a quadruplexer have been fabricated. Good agreements between the simulated and measured results can be observed.