High-Isolation Microstrip Triplexer Using Multiple-Mode Resonators

A microstrip triplexer with high isolation is proposed in this letter. The triplexer utilizes multi-mode resonators, stepped-impedance resonators, and distributed coupling technique. To begin with, we design a diplexer with near passbands according to the excitation condition of the multi-mode resonators. The first passband is excited in odd mode, and the second one is of even mode. In this way, one can improve the isolation. Furthermore, without increasing any circuit size, the diplexer can be promoted to triplexer due to the third channel using distributed coupling technique.