A Wideband Medium-Gain Vertically Polarized Omnidirectional Antenna Array

A medium-gain vertically polarized omnidirectional antenna array (VPOA) with wide bandwidth is proposed in this paper. Initially, a conventional printed dipole antenna with integrated balun (IB) is introduced to use as the wideband element. Then, four antenna elements are alternately arranged in the vertical direction to achieve high gain. Moreover, the four elements are excited by a shunt-fed feeding network which is utilized to provide uniform amplitude and phase for the elements. The feeding network has a common ground with the balun, and it can be easily integrated with the IB. Furthermore, two metallic cylinders placed in the normal direction of the substrate are used as two reflectors to improve the gain variation in the horizontal plane. In order to validate the design method, a prototype is fabricated and measured. The measured results indicate that the proposed antenna has an impedance bandwidth of 56% (1.12-2 GHz) for VSWR <= 2 and a simple structure with lateral size of 0.45 lambda(0) (lambda(0) is the free-space wavelength at center frequency). In addition, stable omnidirectional radiation patterns are obtained with gains around 6.5 dB and the gain variations in the horizontal plane less than 2 dB across the operating band.