Compact and high-isolation microstrip quadruplexer

A microstrip quadruplexer with high isolation and compact size is proposed. The quadruplexer utilizes multimode resonators (MMRs), stepped-impedance resonators, and distributed coupling technique. In this proposed quadruplexer, the first and third passbands are excited in the odd modes of MMR, and the second and fourth passbands are of even modes of MMR. Then, with transmission zeros controlled, one can improve isolation. The quadruplexer occupies only a small area of 0.049λ02, and the isolation is better than 31 dB.

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