A novel quad band branch-line coupler with 3 dB coupling loss is proposed and implemented with real components. It uses dual composite right left handed (D-CRLH) transmission lines designed to work for four frequencies simultaneously, f1 = 1.7 GHz, f2 = 5.2 GHz, f3 = 2.43 GHz, f4 = 3.64 GHz. An algorithm for an efficient designing of the metamaterial lines is presented and validated both analytical and by simulation. The implementation with real components of the branch-line coupler proves to have good performances, exhibiting a directivity up to 37 dB and a phase imbalance less than 0.65o. The other transmission parameters are also very good for all four microwave frequencies and a coupling loss of around 4 dB is achieved in all cases.

Keywords: Quad band branch-line coupler, Dual composite right left handed (D-CRLH) transmission lines, Metamaterials, Microwaves