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Evaluation of methods for estimating the cross-correlation coefficient between closely spaced diversity antennas Hynes, Christopher

Abstract

A growing number of cellular handsets and other personal wireless communications devices use diversity combining and/or MIMO techniques in order to boost link performance and reliability and therefore must incorporate closely spaced antennas. The cross-correlation coefficient between such antennas in fading environments is a key predictor of the success of such schemes. In recent years, several methods for predicting this parameter based upon measurement or simulation of either their field or terminal characteristics have been proposed. Here, we compare the performance of such methods for the case of two closely spaced half-wavelength dipole antennas subject to the assumptions that (1) the angle of arrival distribution is uniformly distributed in three-dimensions, (2) the polarization of the incident waves are uncorrelated to each other and individually uncorrelated in different directions and (3) the cross-polarization power ratio is unity. We consider two diversity antenna configurations. In the first, one antenna is loaded while the other is terminated by an open circuit, e.g., as in the case of switched diversity schemes. In the second, both antennas are attached to matched loads, e.g., as in the case of diversity combining or MIMO schemes. The best results were obtained using isolated far-field pattern coherence when one antenna is open-circuited and both antennas have characteristics approaching those of minimal scattering antennas. However, our results also indicate that the majority of recently proposed methods for estimating the cross-correlation coefficient are surprisingly inaccurate, especially when both antennas are attached to matched loads. Furthermore, we conclude that the total efficiency of the antennas is just as important as their cross-correlation in determining the performance of a multiple antenna system. KEYWORDS: Antenna array mutual coupling, Antenna measurements, Antenna proximity factors, Correlation, Dipole antennas

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