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

This paper describes a new design for a compact tri-band (TB) branch line coupler (BLC) using a modified double-Lorentz (DL) composite right/left handed (CRLH) transmission line (TL). For this design, the positive phase response is selected at the 2nd operating band so that the unit structure of DL CRLH TL yields phase responses of −π/4, π/4, and −π/4 at TB. This structure is employed to operate the TB BLC at 0.195, 0.67, and 1.465 GHz. The proposed TB BLC has a compact size that has been reduced by 85.8% relative to the previous TB BLC where both were designed using DL CRLH TLs for the same TB. The results obtained through a simulation and experimental measurements are in good agreement, and the operating frequencies for all TB are well attained. Thus, the proposed TB BLC is significantly compact and offers steady performances due to its reliable realization, which is very useful for practical applications.