Band-broadening design technique of CRLH-TLs branch-line couplers operating at two arbitrary frequencies using CRLH-TLs matching networks

This paper treats a dual-band branch-line coupler with matching networks which consist of an impedance step and a short-circuited stub based on the equivalent admittance approach. By replacing each right-handed transmission line (RH-TL) with a composite right/left-handed transmission line (CRLH-TL), very flat couplings over a relative bandwidth of about 10% can be obtained at two arbitrary operating frequencies in comparison with previous CRLH-TLs branch-line couplers. Furthermore, by adding periodical open-circuited stubs into RL-TLs of the designed CRLH-TLs branch-line coupler with matching networks, the entire size of the coupler can be reduced to about 50%. Verification of this band-broadening design technique can be also shown by an electromagnetic simulator and experiment.