An omnidirectional horizontally polarized antenna with improved gain is realized by using EBG cavity. The EBG cavity is composed of ring metallic strips etched on thin FR4 substrate and two metallic reflectors installed on up/down sides, which is designed to have a low effective index of refraction (n<1). The metallic strips are arranged in concave shape. Compared with the antenna without EBG cavity, the EBG cavity makes the vertical beam become narrow and effectively improves the omnidirectional antenna gain. An experimental prototype is fabricated to validate the proposed analysis. Measured data show the gain of the antenna with the EBG cavity improved by about 2.72 dBi at 5.7 GHz, and the measured data have a good agreement with numerical results.
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