A Broadband Compact Microstrip Ring Coupler Utilizing a Novel CPW Inverter

A Broadband Compact Microstrip Ring Coupler Utilizing a Novel CPW Inverter is introduced in this paper. The 3/4λ branch of traditional rat-race is composed by two1/8λ microstrip line and a CPW inverter. Defected ground structure(DGS) is used and 1/4λbranches is folded. The footprint of the proposed ring coupler is only 10% of the conventional ring coupler. The coupler's insertion loss is less than 3.5 dB across the frequency band from1 to 2 GHz. The proposed design is less than 0.2 dB amplitude mismatch, less than 5° phase mismatch, and more than 25 dB isolation over the operation bandwidth.