Diversity performance analysis of two parallel dipole antennas mounted on a small metal body

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Abstract
Diversity technology is an effective means to improve the transmission quality in mobile communications. Hence, some portable telephones are equipped with diversity antennas. However no detailed analysis has been carried out. The reason for the low correlation coefficient of such antennas in experiments has not been clarified quantitatively.In this paper, the diversity antenna is assumed to be made of two half‐wave dipole antennas placed in parallel on a small transceiver with a rectangular shape, and its correlation coefficient and efficiency characteristics are analyzed by the method of moments using wire grid models. It is found that the correlation coefficient of 0.23 and the efficiency including the mismatch loss is −2.7 dB even for an antenna element spacing of 0.1 wavelength. Thus a sufficient diversity effect can be obtained on a small transceiver. Specifically, the reason for the low correlation coefficient is studied by separating the mutual coupling between the antenna elements and the effect of the metal body. The relationship between the incoming wave profile and the correlation coefficient is presented. It is shown that the correlation coefficient never exceeds 0.6 in an ordinary operating condition and that the correlation coefficient can be made almost 0 if the load impedance of the parasitic antenna element is chosen appropriately.

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