A Compact Microstrip Quadruplexer Using Slotline Stepped Impedance Stub Loaded Resonators

In this paper, a novel compact quadruplexer is implemented by using slotline stepped impedance stub loaded resonators (SISLRs) in ground plane. Four folded dual-mode slotline SISLRs with one input and four output coupled line structures are designed at different frequencies for the quadruplexer operation. By properly adjusting the geometrical parameters of a single dual-mode slotline SISLR, its first two resonant frequencies can be controlled, and thus it can be utilized to implement a second-order bandpass filter when these resonant frequencies are suitably assigned. Furthermore, because the proposed quadruplexer utilizes the distributed coupling technique, a small circuit size can be obtained. As a result, the proposed quadruplexer occupies an extremely small area, i.e., 0.22λ0×0.25λ0 (0.36λg×0.41λg). Finally, good agreement between measurement and EM simulation verifies the design method successfully.