Miniaturization and Dual-Band Operation in Planar Microwave Components by Using Resonant-Type Metamaterial Transmission Lines

In this work, it is shown that dual-band microwave components based on plusmn90deg metamaterial transmission lines can be miniaturized by implementing the artificial lines by means of complementary spiral resonators (CSRs). Such lines exhibit a composite right/left handed (CRLH) behavior. Dual-band operation is achieved by designing the lines to provide a phase of -90o at the lower operating frequency (within the left handed band) and +90o phase shift at the upper frequency (within the right handed band). Size reduction, as compared to conventional implementations, is achieved by implementing the lines with a single unit cell, and thanks to the small electrical size of CSRs. To illustrate the possibilities of the approach, a dual-band branch-line coupler based on metamaterial transmission lines implemented by means of CSRs is presented. The device has been designed to be functional at the mobile GSM bands (f₁= 0.9 GHz, f₂= 1.8 GHz). As compared to the conventional branch line, a 40% size reduction is obtained. The approach is fully compatible with planar technology.