Design of a Broadband High-Gain End-Fed Coaxial Collinear Antenna

Abstract

Omnidirectional antennas are widely used for mobile communications in the base transceiver station. This letter introduces a high-gain coaxial collinear (CoCo) antenna with a stable radiation pattern. To design a wideband end-fed CoCo antenna, we modify the classic center-fed CoCo antenna structure with an appending wire-mesh structure. The proposed CoCo antenna's −10 dB impedance bandwidth and gain bandwidth (1 dB variation of maximum gain versus frequency) at a center frequency of 900 MHz is three times higher than the classical center-fed CoCo's equivalent bandwidth, thus retaining 9 dB gain. The unique feeding configuration is designed to create the broadband end-fed antenna and minimize the feeding cable effect on the omnidirectional radiation pattern. We prototype an antenna to evaluate the design performance and confirm the simulation results. The measured results show 8.5 dBi directivity and 125.5 MHz bandwidth at 900 MHz center frequency. Index Terms-Antenna feeds, coaxial collinear (CoCo) antenna, high-gain omnidirectional antenna, wideband antenna. I. INTRODUCTIONB ROADBAND and high-gain omnidirectional antennas are in ever-increasing demand due to the rapid development of wireless communications and sensing systems. Most on-demand mobile communication systems require vertical polarization antennas in their base transceiver stations (BTSs) that concentrate the transmitted power in all horizontal directions at low heights above ground or water. In such applications, while having broad bandwidth and high radiation gain are very important, the stability of the radiation-pattern peak is also necessary. Furthermore, in specific low-frequency applications, omnidirectional antennas with high radiation efficiency, low weight, minimal cost, ease of manufacturing, and portability are desired [1]-[9]. However, it is still a significant challenge to incorporate all these favorable characteristics into an omnidirectional antenna, which forms the main focus of this letter.The coaxial collinear (CoCo) antenna was introduced by Wheeler [1] based on the Franklin antenna concept. This antenna was developed theoretically and experimentally over the years [2], [10]-[14] and is considered a high-gain omnidirectional antenna, particularly in VHF/UHF bands, thanks to its simple feeding mechanism and easy manufacturing. The CoCo antenna can be used either as an isolated antenna element or as an element in a large antenna array [15], [16]. Note that the gain of Manuscript

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