New rat-race couplers that can be
operated at two separate frequency bands are
presented. The design is accomplished by
transforming the lengths and impedances of the
conventional rat-race into dual band T or П
shaped sections. Simple design equations are used
for basic design geometries. Then the rat-race
coupler geometries are analyzed using a full wave
electromagnetic (EM) simulator and then realized
at 0.9425 and 1.96 GHz for global system of mobile
communications (GSM) bands. Excellent
agreement between simulated and measured
results demonstrates the performance of the
proposed couplers. Both ring structures have a
wide frequency operation range in addition to the
significant reduced-size of the П-section based
coupler.
Index Terms- Ra