A compact microstrip quadruplexer with high isolation is presented in this letter. The quadruplexer consists of a distributed coupling feeding line, output feeding lines and uniform resonator pairs. Since the uniform resonators would resonate at multiple fundamental frequencies, to obtain a high-isolation quadruplexer, the resonators are properly located with respect to the input and output feeding lines to suppress the harmonic responses. Furthermore, because each pair of resonators control a specific channel frequency independently and the loading effect among channels is very small, the proposed quadruplexer has flexible passband frequencies.
