Novel Planar Negative Refractive Index Metamaterials G. Goussetis, A. P. Feresidis, Y. Guo, and J. C. Vardaxoglou Wireless Communication Research Group, Department of Electronic and Electrical Engineering, Loughborough University, UK Loughborough University, UK Abstract Planar periodic arrays of metallic elements printed on grounded dielectric substrates are presented to exhibit first-order left-handed modes with an equivalent negative refractive index (NRI) [1]. The proposed structures dispense with the need for grounding vias and ease the implementation of completely planar (also called uniplanar) NRI metamaterials at higher frequencies. Full wave dispersion curves are presented. A verification of the left-handedness is presented by means of full wave simulation of finite uniplanar arrays using commercial software (HFSS). The cell dimensions are a small fraction of the wavelength (about λ/24) so that the structures can be considered as a homogeneous effective medium. The structures are simple, readily scalable to higher frequencies and compatible with low-cost fabrication techniques. Negative refractive index planar designs Negative refractive index (NRI) metatamaterials support left-handed propagation, i.e. the vectors E, H and k form a left-handed triplet. For NRI metamaterials the phase velocity (ω/β) and the group velocity (dω/dβ) are anti-parallel. The dispersion relation of the first order mode for NRI metamaterials therefore has negative gradient [2-3]. Our initial investigation has shown that moving from the square split loop element to the rectangular split loop the first resonant mode changes from right-handed to left-handed. We therefore focus our study on a rectangular unit cell with an edge ratio of 2:1. The unit cells of the arrays discussed hereafter are shown in Fig. 1. Figure 1 shows the unit element of (b) a split rectangular loop, (c) a capacitive-loaded split rectangular loop and (d) a spiral-loaded rectangular loop arrays. For completeness, the closed rectangular loop (Fig. 1a) is also discussed. The unit cell is kept constant throughout (3mm × 6mm). All metallic line widths are 0.2 mm and the gaps in the split loop variations are s=0.2 mm, t=0.4mm, in order to be compatible with conventional photolithographic techniques. The element dimensions are L=5.8mm and W=2.8mm. The dielectric substrate has a dielectric constant of 2.2 and thickness 1.13 mm. In order to derive the dispersion characteristics of the arrays under consideration we employ an analysis based on method of moments [4]. Triangular basis functions are used that allow for modelling of arbitrary shaped metallic elements. In order to derive the generic solution for allowed modes, non-trivial solutions of 0-7803-8883-6/05/$20.00 ©2005 IEEE