High Directivity Coupler Suppressing Leak Coupling with Cancellation Circuit of Wilkinson Divider

A high directivity microstrip coupler suppressing leak coupling 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 microstrip coupler to enhance the isolation. The cancellation circuit consists of the Wilkinson divider, the multistage attenuator, and the phase offset line. The frequency to enhance the isolation is controlled by the attenuators. As the directivity is improved without the modification of the conventional coupler, the cancellation circuit can be applied to the fabricated conventional couplers. The measured directivity of the presented 1/18 lambda coupler is improved from 4.8dB to 43.0dB at 2.6GHz, compared with the conventional 1/4 lambda coupler with -20dB coupling. Simultaneously, the 27.4% relative bandwidth with the 20dB directivity is achieved.