Low-profile mimo antenna arrays with left-handed metamaterial structures for multiband operation

Abstract

In this article, a design of two low-profile multiple-input-multiple-output (MIMO) antenna arrays based on left-handed metamaterial (LHM) structures is proposed for multiband wireless applications. The single-element antenna is a monopole antenna fed by a microstrip transmission-line loaded with a single LHM unit cell. The LHM unit cell structure consists of a right-angled bend interdigital capacitor and dual symmetrical right-angled bend shorted stub inductors. The loaded monopole antenna was previously designed to operate in the left-handed (LH) frequency region at three negative-order resonance modes (i.e., 1.39, 1.88, and 2.35 GHz). Herein, to increase the designed antenna performance in wireless communication systems, two-and four-element MIMO antenna arrays having compact sizes with overall dimensions of 21×35 mm2 and 35×35 mm2, respectively, are realized. A close uniform edge-to-edge separation between antenna elements of each configuration equals only 2mm (0.0093λ0 at 1.39 GHz), and port isolation more than 18 dB over the entire operating bands is obtained without using extra isolation structures. Envelope correlation coefficient is evaluated, showing good field isolation. The performance of the assembled MIMO antenna arrays is verified numerically and experimentally. The given attributes make the proposed antenna arrays a suitable candidate for multiband MIMO applications.