A study of meandered microstrip coupler with high directivity

Abstract

A novel design technique to improve the directivity of a microstrip direction coupler by a meandered structure is proposed in this paper. Increasing of even-mode phase velocity by the proposed meandering method is reported for the first time. An analytical method to obtain closed-form equations of even-mode phase velocity is developed. The proposed structure is verified by experiments. More than 40 dB measured directivity improvement comparing to conventional microstrip coupler is achieved.