An omni-directional array antenna composed of ring slots covered with metallic cylinders

An omni-directional antenna element using a ring slot as an exciter and a metallic cylinder as a radiator is proposed. The metallic cylinder behaves as a parasitic element so that the element can realize broad frequency bandwidth and a uniform omni-directional pattern. Using this element we have made a vertical array antenna for a 2GHz-band W-CDMA system. All elements of the antenna are fed by parallel feeding system, and this antenna realizes more than 10% frequency bandwidth. Nevertheless it has a relatively thin configuration and the radiation tilt angle can be precisely adjusted. In this paper the principles of the element and characteristics of the array are described.