Miniaturization technique for forward-wave directional couplers by using open stubs and patterned ground structures

A novel compact 3-dB forward-wave directional coupler using periodic open stubs and patterned ground plane is proposed. Not only can the input impedances of the even and odd modes be matched, but also the phase difference between the two modes is largely enhanced. The size of the proposed coupler can be reduced significantly. A test sample is fabricated on Duroid substrate. The 3.3 dB coupling level of proposed coupler can be measured at 1.47 GHz. The size reduction of proposed structure is about 95 %. Compared to the previous works, the proposed coupler can be designed with a smaller size.