Double loops coupling structure and its application in the multicoupler

In the cavity broad-band UHF multicouplers,the equivalent electric length in the port of the cavity filters is usually too long,which reduces the multicoupler performance.To solve this problem,a double loops input/output coupling structure used in the cavity tunable bandpass filter is proposed in this paper firstly. Then the theoretical analysis and the simulated-experimented verification of this structure are also carried out.The results show that provide adopting this structure, the reflection characteristic of the tunable filter stop band can be adjusted independently with only little influence to its performance of pass band.The equivalent electric length in the port of the cavity filters can also be reduced efficiently.Finally, a coaxial-cavity tunable filter using double loops input/output coupling structure is designed and a 4-ways multicoupler constituted of four tunable filters is fabricated. The experimental results reveal the validity of this structure.