Abstract-In this paper a dual band circularly polarized antenna is designed, fabricated, and measured. Based on the concept of composite right and left handed (CRLH) metamaterials, the same phase constants and current distributions on the ring antenna are achieved at two frequency bands. Thus, the antenna has similar radiation patterns at both bands. The circular polarization is implemented by feeding two vertical ports from power dividers that provide equal magnitudes and quadrature phase excitations.

In the design procedure of a reflectarray antenna system, the aperture efficiency needs to be first analyzed to forecast the system performance. This article investigates the effects of the reflectarray configuration parameters on the antenna aperture efficiency. A general approach is introduced to calculate the spillover efficiency of a reflectarray with arbitrarily shaped aperture and feed scheme. Meanwhile, the illumination efficiency of the reflectarray is analyzed with a unified set of equations. On the basis of these derivations, parametric studies are performed to provide design guidelines for optimizing the aperture efficiency of reflectarray antennas. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 364–372, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24949

1619the hollow shell needs to have r 390 to yield Q=Q Chu = 1:05, whereas the magnetic coating on the PEC core requires only r 100 to reach the same Q=Q Chu = 1:05. IV. CONCLUSIONThe radiation problem for the TM 10 electric current on the surface of a material-coated spherical PEC core is solved analytically using vector spherical wave functions. Closed-form expressions for the electric and magnetic stored energy as well as for the radiation quality factor Q are presented. The optimum relative radius of the PEC core b=a providing the lowest possible Q for a given antenna electrical size ka and material parameters "r and r of the coating is found. It is shown that a PEC core with an electrically thin high-permeability magnetic coating significantly reduces the internal stored energy, and thus the Q of the electric dipole antenna closely approaches the Chu lower bound. For instance, an antenna of the size ka = 0:5 with the relative radius of the PEC core b=a = 0:975 and a pure magnetic coating with r = 400 yields the quality factor Q = 1:01Q Chu . REFERENCES[1] L.

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