Design of a compact dual-band branch line coupler using composite right/left-handed transmission lines

The design of a compact dual-band (DB) branch line coupler (BLC) using composite right/left-handed (CRLH) transmission lines (TLs) is described. By properly choosing the parameters of the CRLH TLs, the structure yields phase responses of π/2 and -π/2 at two arbitrary operating frequencies. Employing this structure, a DB microstrip BLC operating at 0.93 and 1.78 GHz is achieved. The size of the proposed DB BLC is significantly compact, at 34.4% of the previous DB BLC when they are both designed using CRLH TLs for the same DB frequencies. The simulated and measured performances of the proposed DB BLC are reliable compared with those of the previous DB BLC.