This article presents a dual-band rat-race coupler for high band ratio wireless applications. In this article, a dual-band transmission line (TL) has also been proposed to design the rat-race coupler. The proposed rat-race coupler has been developed by substituting each TL segment of a single-band rat-race coupler with the dual-band TL. To validate the design method, a rat-race coupler for 0.7- and 4.9-GHz operating frequencies has been developed. A maximum of 3.3-dB insertion loss and 20-dB return loss and isolation have been attained for both the frequency bands. Compared with the existing dual-band rat-race couplers, the proposed coupler offers dual-band operation with a high band ratio. In addition, for the first time a dual-band rat-race coupler compatible with microstrip TL and having input and output on different sides has been developed. This feature makes simpler connections when connected to other circuits.