Dual-band rat race hybrid coupler implemented through artificial lines based on complementary split ring resonators

A dual-band rat race hybrid coupler based on artificial lines implemented by means of complementary split ring resonators (CSRRs) is presented for the first time. Contrary to other dual-band components (such as branch line hybrid couplers or power dividers) based on the composite right/left handed (CRLH) characteristics of CSRR-loaded lines, the present design approach is based on the diplexer action of pairs of artificial lines; one of them designed to exhibit right handed wave propagation and the other one left handed wave propagation at the lower and upper frequency bands, respectively. The fabricated device is slightly smaller than the conventional (mono-band) rat race hybrid coupler, and it exhibits good performance. Full compatibility with planar technology and arbitrariness of the operating frequencies are advantages of the approach.