Design Method of Miniaturized Ring Coupler Using Phase Shifters Consisting of Fully-Distributed Composite Right/Left-Handed Structures

A new method to design a miniaturized ring coupler consisting of multiple open stubs on the inside of the ring is proposed. It is shown that this coupler topology may be seen as fully-distributed composite right/left handed (CRLH) small-size phase shifters, cascaded in a ring configuration. The CRLH phase shifter is analyzed in detail and a design method is proposed, pointing out the condition to obtain a reduction of its length. Using the fully-distributed CRLH based phase shifter, a ring coupler is configured and analyzed in comparison with the traditional ring coupler, showing that both couplers have similar characteristics. To validate the proposed design method, a 3-dB CRLH based ring coupler is designed and fabricated. The experimental results show a very good agreement with the predicted results obtained by electromagnetic simulation. The printed area of the fabricated coupler is 49% smaller compared to the traditional ring coupler.