Aiming at the problems of narrow frequency tuning range and large volume of coaxial cavity electrically tunable duplexer, the influence of the external Q value and the coupling coefficient on the passband bandwidth of the tunable filter is studied and analyzed,the reason why the tuning range of the filter becomes narrow due to the frequency detuning of the cavity is also analyzed,The paper proposes a porous coupling structure and a processing method to solve the resonance frequency detuning, A compact UHF band duplexer is designed. The experimental results show that the diplexer can achieve miniaturization, high selectivity and basically constant absolute bandwidth, Among them, the two filters can be tuned synchronously to maintain the characteristics of the same frequency.