A compact and low-profile metamaterial ring antenna with vertical polarization

A compact (lambda(0)/11 footprint) and low-profile (lambda(0)/28 height) metamaterial ring antenna is proposed using two metamaterial unit cells. Each constituent unit cell consists of negative-refractive-index (NRI) microstrip transmission lines (TL) designed to incur a zero insertion phase at the antenna design frequency. This allows the inductive posts to ground, which act as the main radiating elements, to be fed in phase. Hence, the antenna operates as two closely spaced monopoles that are fed in phase through a compact feed network. An embedded matching network ensures good VSWR performance. The theoretical performance of the antenna is verified by full-wave simulations and experimental data obtained from a fabricated prototype at 1.77 GHz. The antenna offers a 120 MHz -10 dB bandwidth and a measured efficiency exceeding 50%.