Abstract
In this article, a negative index metamaterial antenna is presented for ultrawideband (UWB) microwave imaging applications. Four left-handed (LH) metamaterial (MTM unit cells are located along one axis of the antenna as the radiating element. Each left-handed metamaterial unit cell assembles a modified split-ring resonator with a capacitance-loaded strip to obtain a design architecture that at a time shows both negative permittivity and negative permeability, which assures the stable negative refractive index to raise the antenna performance for microwave imaging. The antenna structure of dimension 16 x 21 x 1.6 mm(3) is printed on low dielectric FR4 material with a slotted ground plane and a microstrip feed. Measured reflection coefficient illustrates that this antenna attains 114.5% bandwidth covering the frequency band of 3.4-12.5 GHz for a voltage standing wave ratio less than 2 with a maximum gain 5.16 dBi at 10.15 GHz. There is a stable harmony between simulation and measured results and improved nearly omnidirectional radiation characteristics within the operational frequency band. The stable surface current distribution, negative refractive index characteristic, considerable gain, and radiation property have made this proposed negative index metamaterial antenna distinguishable for UWB microwave imaging applications. (c) 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1352-1361, 2015