The effects of antenna gains and polarization on multipath delay spread and path loss at 918 mhz on cross-campus radio links

This paper presents results of delay spread and path loss measurements across a large college campus, and illustrates how antenna gain and polarization should be selected for line-of-sight microwave links between buildings. Two line-of-sight links were used with three different types of antennas to determine best polarizations and pointing angles. Measurements show multipath is most severe when antennas of different polarizations are used on each end of the link. Minimum delay spreads are encountered when antennas of the same polarization are used and pointed directly towards each other. As long as polarizations are matched on each side of the link, polarization does not have significant impact on delay spread or path loss. A somewhat surprising result, however, is that circularlypolarized helical antennas offer multipath reduction over a wide range of pointing angles. This suggests that on point-to-point cross-campus links where a single antenna is desired to serve a broad coverage area, circular polarization could be used in lieu of channel equalization to improve bit-error-rates in high speed data networks.