Aiming at the problem of narrow frequency tuning range and large volume of coaxial cavity electrically tunable duplexer, the influence of external Q value and the coupling coefficient on passband bandwidth is studied and analyzed, as well as the reason of narrow tuning range caused by frequency detuning of resonant cavity. A porous coupling structure and the treatment method to solve the resonance frequency detuning are put forward, and a compact UHF band electronic duplexer is designed. The experimental results show that the duplexer can achieve the effect of miniaturization, high selectivity and constant absolute bandwidth, in which two sets of filters can be tuned synchronously to maintain the characteristics of the same frequency.