Compact rat-race coupler with double-sided parallel-strip line (DSPSL) for dual-band arbitrary power divisions

Dual-band rat-race couplers are implemented with double-sided parallel-strip line to provide arbitrary power divisions. Both the uniform-impedance and stepped-impedance cases are explored, and design equations are derived for the two cases. With our method, the rat-race coupler can be quickly developed to satisfy the design specifications. By using phase inverter, arms with arbitrary electrical lengths and characteristic impedances, the areas of components are reduced by 79.5% and 88.6% in comparison with the conventional rat-race coupler. The good performances of the proposed couplers have been demonstrated by their measured and simulated results.