A dual band omni-directional antenna for cellular mobile radios

Abstract

IMT-2000 is the dominant 3rd generation cellular system that uses the 2 GHz band. In Japan, its base station antennas must be integrated into those of the conventional PDC (personal digital cellular system using 0.9/1.5 GHz) because antenna construction space is extremely tight. When using IMT-2000, we want to use simple base-station equipment and omni-directional antennas. Accordingly, we plan to use dual-band (0.9/2.0 GHz) omni-directional base station antennas in rural areas. Dipole or monopole antennas are generally used as omni-directional antennas. However, the feed lines, needed to control electrical down tilting in the vertical plane, influence the horizontal pattern, making it very difficult to get a good omni-directional pattern. To improve the pattern, two dipole antennas can be arranged on opposite sides of a square type reflector which covers the feed lines. However, in a dual-band antenna, twice as many feed lines are needed, so that the cylindrical reflector becomes too big or the feed lines do not lie underneath the reflector; and it is difficult to achieve slender antennas. We propose a slender type base station antenna whose radiation pattern in the horizontal plane is omni-directional in both the 0.9 GHz and 2.0 GHz bands. This antenna eliminates the antenna construction space problem.