Design ofDual-Band Microstrip RatRaceCoupler withCircuit Miniaturization

Ratraceringcoupler withstepped-impedance sections isdesigned tohaveadual-band characteristic. Thisis realized byattaching openstubs tobothendsofeachstepped- impedance section tocreate aphaseof900attwodesignated frequencies. Transcendental equations arederived forsolving impedance ratio R andlengths ofthestepped-impedance sections. Circuit withminiaturized areacanbeobtained ifR >1ischosen. Suchmicrostrip ring hybrids operating at2.45/5.2 GHzwithR = 1 andR = 4 aredesigned andfabricated. Experiments are performed toconfirm thetheory. IndexTerms - Directional coupler, dual-band, miniaturiza- tion, ratracecoupler, stepped-impedance.