On design optimization of miniaturized microscrip dual-band rat-race coupler with enhanced bandwidth

In the paper, a novel topology of a miniaturized wideband dual-band rat-race coupler has been presented. Small size of the circuit has been obtained by meandering transmission lines of the conventional circuit. At the same time, the number of independent geometry parameters has been increased in order to secure sufficient circuit flexibility in the context of its design optimization for dual-band operation. Optimum dimensions of the coupler have been obtained through automated simulation-driven design involving surrogate-based techniques. The operating frequencies of the coupler are 1 GHz and 2 GHz, whereas a −18 dB bandwidth is as wide as 22.5 and 11.3 percent for the lower and upper band, respectively. The miniaturization rate is over 37 percent compared to the conventional structure. The design is validated through full-wave EM analysis at fine discretization.