Novel dual band hybrid rat-race coupler with CRLH and D-CRLH transmission lines

A new dual band rat-race coupler with left handed transmission lines is presented in this paper. The main advantage of this novel coupler is that there are used a reduced number of cells, meanwhile the performances improve. In order to reduce the dimensions of the coupler, the 3λ/4 CRLH transmission line has been replaced with a D-CRLH transmission line, and moreover there have been introduced a new method to design quarter wavelengths CRLH/D-CRLH transmission lines with minimum number of cells. Also, the dual version of this hybrid coupler, that is made of three identical CRLH transmission lines and one D-CRLH is the hybrid coupler that has three identical D-CRLH transmission lines and only one CRLH transmission line. In fact, the main idea of the hybrid rat-race coupler is to use the duality between the CRLH and D-CRLH transmission lines, which implies in this particular case, to replace a transmission line that introduces a phase shift of 2700° with a transmission line introducing a phase shift of -90°, and vice versa. It is important to notice, that this coupler can be designed to operate at two arbitrary frequencies like all microwave devices that use LH transmission lines.