Broadband rat-race coupler in suspended stripline technique for measurements of large-signal S parameters

A broadband rat-race coupler has been designed in a suspended stripline technique. For broadband operation the needed phase inverter has been realized as a shorted-coupled-line section. Additionally single section matching transformers have been added to improve the return losses. The suspended stripline technique has been chosen for minimizing the coupler's losses. The described circuit has been experimentally verified, manufactured and measured. The measurement results show a good agreement with both circuit and electromagnetic analyses which prove the correctness and usefulness of the presented design. The application of the designed rat-race coupler in large-signal S parameter measurements have been discussed.