The configuration of two parallel half-wave dipoles is the basic spacediversity branch for spacediversity reception in mobile radio communications. This paper presents theoretical and experimental study on the antenna diversity branch connected to a 50ohm receiver. Postdetection selection diversity is applied to determine the relation of the mean effective gain (MEG) and the correlation coefficient with the variation of angle of antenna inclination from the vertical direction, cross-polarization power ratio (XPR) of the propagation path, and the distribution of the incident wave.
First, it is clarified theoretically that, if antenna spacing is made less than 0.2 wavelength, then efficiency is reduced due to the coupling between the antenna elements and MEG is greatly deteriorated. Moreover, minimum antenna spacing for better MEG characteristics is in the range of 0.3 to 0.4 wavelengths.
Next, it is clarified that the correlation coefficient is less than 0.1 for variation of antenna inclination, XPR, and the distribution of incident wave when the antenna spacing ranges from 0.2 to 0.3 wavelengths. Thus, an optimum antenna spacing exists in the forementioned spacediversity branch, which theoretically is found to be about 0.3 wavelength. The validity of the theoretical results is confirmed by 900-MHz band indoor experiments.