Computer-Aided Tuning of Butler Matrices

This article proposes a computer-aided tuning approach for Butler matrices (BMs). It is implemented in two stages. First, extract the amplitude imbalance of each individual coupler from the overall BM measurement results using the proposed diagnosis procedure. The extracted results led to the instructions for fine adjustments. After that, each coupler is adjusted using the proposed method. As a result, the nonideal effect of a BM can be tuned out to achieve significant performance improvement. An
$8 \times 8$
BM was designed, fabricated, and tuned using the proposed approach. The final results show excellent amplitude imbalance performance, which is improved by more than 80% relative to the initial results. For the first time, a systematic tuning method is demonstrated to achieve excellent amplitude imbalance for a BM.