ELECTROMAGNETIC APPLICATIONS OF NEGATIVE-REFRACTIVE-INDEX TRANSMISSION-LINE METAMATERIALS

. In this work, “left-handed” metamaterials are considered for which their permittivity and permeability are both negative. These metamaterials exhibit backward-wave propagation characteristics and therefore a negative index of refraction as was predicted in the visionary work of Victor Veselago [1]. Such “left-handed” or “Negative-Refractive-Index” (NRI) media were first implemented using bulk periodic arrays of thin wires to synthesize negative permittivity and split-ring resonators to synthesize a negative permeability [2]. However, the size of the NRI medium presented in [2] renders it impractical for the physical realization of planar microwave circuits and antennas. More recently, a completely planar approach for synthesizing NRI media was proposed in [3],[4]. The 2-Dimensional (2-D) NRI structure presented in [3],[4] was realized by periodically loading a planar network of printed transmission lines (TL) with series capacitors and shunt inductors in a dual-TL (high-pass) configuration. The 2-D NRI medium was subsequently interfaced with a commensurate conventional dielectric, leading to the first experimental demonstration of focusing from a NRI metamaterial [4], [5]. More recently, a 3-region lens arrangement was used to observe focusing beyond the diffraction limit [6]- [8] as was predicted by J.B. Pendry [9]. A similar TL approach was followed by Itoh and Caloz and led to interesting structures and circuits [10], [11]. Moreover, intriguing and useful anisotropic transmission-line metamaterials have been reported by Balmain in [12]. Some of the first FDTD simulations of NRI media have been reported in the pioneering work of R. Ziolkowski et al. in [13]. Further developments in the general area of Metamaterials can be found in two recent special issues: The October 2003 issue of the IEEE Transactions on Antennas and Propagation (Guest Editors N. Engheta and R. Ziolkowski) and the April 2003 issue of Optics Express (vol. 11, No. 7, Guest Editor J.B. Pendry ). This work presents various electromagnetic applications and devices that have been developed at the University of Toronto using Transmission-Line Negative-Refractive-Index (TL-NRI) metamaterials. A brief description of the effective-medium theory for TL-NRI media is presented first. This is followed by various TL-NRI applications and devices, including a super-resolving planar lens, a leaky backward-wave antenna radiating its fundamental spatial harmonic, compact broadband antenna feed-networks and a coupled-line coupler with co-directional phase but contra-directional power flow.