High Directivity Quarter-wave Microstrip Coupler with Cancellation Circuit of Wilkinson Divider

A high directivity quarter-wave microstrip coupler with a cancellation circuit of a Wilkinson divider is presented. The presented coupler utilizes a cancellation circuit between a coupling port and an isolation port of the conventional quarter-wave microstrip coupler to enhance the isolation at the desired frequency. The cancellation circuit consists of the Wilkinson divider, and an attenuator. The frequency where the isolation is enhanced can be controlled by the attenuator. The cancellation circuit can be applied to the couplers that have already been fabricated. The measured directivity of the presented coupler is improved from 8.9 dB to 24.9 dB at 1.9 GHz, compared with the conventional coupler.