Applications of resonant-type metamaterial transmission lines to the design of enhanced bandwidth components with compact dimensions

In this article, it is demonstrated that metamaterial transmission lines implemented by means of complementary split rings resonators are useful for the design of planar microwave components with small dimensions and broad operational bandwidths. These characteristics are achieved thanks to the small electrical size of complementary split rings resonators and to the controllability of the dispersion diagram in such artificial lilies. The technique is illustrated by means of the design of a rat-race hybrid coupler. The performance and size of this metamaterial-based component is compared with those characteristics and dimensions of the classical (distributed) implementation. It is clearly demonstrated that by replacing the conventional transmission lines in the design with metamaterial transmission lines conveniently engineered, the functionality of the device is preserved over broader bandwidths and, additionally, significant size reduction is achieved. These characteristics and the absence of lumped elements in the design are of interest for applications in which cost and compatibility with fully planar technology are fundamental aspects. The most relevant contribution of the article is the demonstration of the compatibility between the resonant artificial lines and the design of broad band and high performance microwave components. (C) 2007 Wiley Periodicals, Inc.