COMPACT ANTENNA ARRAYS FOR MIMO APPLICATIONS Marin Stoytchev (1) + , Hugo Safar (1) , Aris L. Moustakas (2) , Steve Simon (2) (1) Agere Systems, 700 Mountain Ave, Murray Hill, NJ, USA (2) Lucent Technologies, Bell Laboratories, 700 Mountain Ave, Murray Hill, NJ, USA Abstract: We use antenna-antenna interactions to reduce spatial correlations among antenna elements, which allows for closely packed arrays for MIMO applications in small portable devices. The reduction in spatial correlations is a result of the modification of the antennas’ radiation pattern when the elements are brought close to each other. We show how a particular dielectric antenna element can be manipulated so that closely placed elements have either nearly isotropic radiation patterns or more anisotropic ones. Accordingly, we find that in a multiple- scattering environment the correlation between antennas with isotropic pattern has the oscillatory behavior with period ~λ expected for a 3D Rayleigh fading environment. On the other hand, antennas with anisotropic pattern show low degree of spatial correlation of ~ 0.2 independent of the antenna separation. Electromagnetic simulations confirm our experimental observation and provide a path for a systematic design and optimization of compact antenna arrays. Introduction: Multiple-input multiple-output (MIMO) techniques have attracted a great deal of attention with their potential to achieve high data transmission rates. [1] Central to these schemes is the existence of independent spatial channels allowing simultaneous transmission and reception of independent streams of information. Thus, correlation between antennas could be crucial for the performance of the system. In the case of a rich scattering environment (Rayleigh fading), separating the elements in the receive and transmit arrays by at least λ/2 would ensure the required channel independence. While this does not present a problem in a base station, accommodating multiple-antenna arrays in a small portable device with such a separation between antenna elements might not be possible. In this work, we demonstrate that one can use antenna coupling to build compact antenna arrays with very low correlations between different elements, which makes possible the implementation of MIMO techniques in small terminals. By taking advantage of antenna-antenna interactions, we build arrays in which each element’s radiation pattern has lobes of maximum gain oriented towards different regions of the space, thus effectively de-correlating the received signals regardless of the separation among the antenna elements. Antenna elements: We use dielectric antenna elements (product of Toko, Inc. [2]) designed for use in wireless modems for laptop computers (Fig 1a). The manufacturer’s suggested use is mounting the element on a ground plane that is large compared to the size of the antenna. However, since our objective is to study correlations between antennas that are separated by small distances we use two different antenna realization based on the original element that are schematically presented in Fig. 1b,c. In the first case (b), we use a circular ground plate with a radius of ~ λ/4, while in (c) the ground plate is eliminated completely. Measurements of the gain and the radiation patterns show that both antennas are linearly (vertically) polarized and have resonant frequencies at 2.50 and 2.60GHz, respectively. Fig. 1: (a) image of the antennas used; schematic presentation of elements with (b) and without (c) a ground plate. (a) (b) (c) (a) (b) (c) 0-7803-7070-8/01/$10.00 (c)2001 IEEE