Design of Small Rectangular Patch Coupler

A new type of miniaturized rectangular patch coupler using a symmetric cross groove is introduced in the paper. By etching a group of grooves on the rectangular patch, the dimension of coupler is reduced largely. The realized two couplers have coupling degree of 3 and 6.7dB and operate in the 5.5 GHz band. The 3dB has a 1dB amplitude unbalanced bandwidth of 20% and the $90^{\circ}\pm 5^{\circ}$ phase difference bandwidth of 27.2%. For the 6.7 dB coupler, the corresponding values are 12.7% and 12.7%, respectively.