Rat-Race Hybrid Ring Realized In Two-Layer Printed Process

New structure for a Rat-Race hybrid ring is proposed, which uses a two-layer printed process, such as the double sided printed circuit board or a two-layered thin-film process. The structure has two transmission-lines crisscrossing each other that are placed at an optimum position where the coupled signal minimally affects the original function of the Rat-Race hybrid. The proposed structure is realized at 60 GHz center frequency. At 25 % relative-bandwidth, the measured balanced mismatches are within 0.6 dB and 10 degrees, while the return-losses and isolations are all 15 dB or more.