Compact Broadband Rat-Race Coupler in Multilayer Technology Designed with the Use of Artificial Right- and Left-Handed Transmission Lines

The paper presents a compact broadband rat-race coupler for the first time designed and realized in a mul- tilayer microstrip technology. To achieve both broad operational bandwidth and a compact size the 270? transmission line of a conventional rat-race, coupler has been replaced by a -90? left-handed transmission line realized with the use of a quasi-lumped element technique. Moreover, to achieve better compactness of the resulting coupler, all 90? right-handed transmission lines have been realized with the use of the same technique. It has been also proved that simple LC approximation of a left-handed transmission line can be successfully used for the design. Moreover, it has been shown that when appropriately chosen, the multilayer dielectric structure allows for realization of structures designed with the use of this simple approximation, for both right-handed and left-handed transmission lines, without loosing too much of a performance