Antenna Applications of Negative Refractive Index Transmission-Line (NRI-TL) Metamaterials

Abstract

One-dimensional (1D) and to a lesser extent two-dimensional negative refractive index transmission-line (NRI-TL) metamaterials and corresponding antenna applications have been presented. An expression for the total phase shift per-unit-cell of a 1D NRI-TL has been derived, and a technique to ensure that these metamaterial lines operate in the slow-wave regime, and therefore do not radiate, has been presented. Subsequently, various antenna feeding devices have been designed and implemented based on NRI-TL metamaterials. Specifically, a compact and broadband series power divider and a corresponding series-fed linear antenna array with reduced beam squinting have been demonstrated. A leaky-wave antenna radiating in the forward direction has also been shown to exhibit reduced beam squinting. Moreover, an electrically small/low profile ring antenna radiating vertical polarization has also been described. One-dimensional and two-dimensional leaky-wave antennas capable of producing forward or backward beams have also been outlined. Other antenna related NRI-TL devices have been presented including a broadband Wilkinson balun and a coupled-line metamaterial coupler featuring high directivity and low coupling levels for antenna signal monitoring applications. Some of these and other developments in NRI-TL metamaterials, as well as recent developments in other NRI metamaterial technologies, can be found in Ref. 67. © 2008 by John Wiley & Sons, Inc. All rights reserved.