Isolation-improved branch-line coupler based on feed-forward technique

In this paper, the improved feed-forward technique to enhance the isolation of a Tx/Rx is presented. It is particularly suitable for Tx/Rx antenna applications and also could be implemented in MMICs. It is achieved about -55 dB isolation after applying feed-forward technique to the branch-line coupler. The proposed feed-forward structure is implemented using the branch-line coupler, the coupled line and the Wilkinson combiner, especially consisted of only microstrip lines, without implementation of other devices like phase shifter and attenuator or application of multi-layer, at ISM band of 5.8 GHz.