A Compact Metamaterial-Based Antenna for Multiband Phased Array Applications

In this article we present a miniaturized multiband metamaterial-based antenna for array applications, operating with good radiation performance over the LTE and UMTS uplinks within the 800–3000 MHz range. Each antenna element consists of a radiator and a metamaterial reflector. The former is a miniaturized Archimedean spiral antenna with an integrated matching line. The latter is placed 39 mm below the radiator and is shared among the multiple elements in the array application. The radiator is very compact, a square of 75 mm per side, equivalent to only 0.2 (0.75) times the free-space wavelength at 800 MHz (3000 MHz). The reflector is incorporated to achieve half-space radiation and is implemented with a novel multi-layered metamaterial structure to improve the radiation efficiency. The metamaterial, moreover, is used in a non-conventional way. In fact, we take advantage of its complete phase-response function, behaving, thus, as magnetic or electric conductor in different parts of the band. In this way, the in-phase reflection is not limited by the typical narrow bandwidth of artificial magnetic conductors. The measured S11 parameter is less than -8 dB and the simulated gain is greater than 4.2 dBi in a range exceeding the one covered by the UMTS and LTE uplinks. Furthermore, a 2×2 antenna array was also built. The reflections of each element are similar to those obtained in the single-element antenna.