Wideband and compact horizontally polarized omnidirectional antenna using composite dipole elements

A wideband horizontally polarized (HP) omnidirectional antenna is constructed and experimented in this article. The antenna consists of four composite dipoles forming a circular array in the azimuth plane and four pairs of parallel strip lines as impedance transformer networks. Two kinds of dipoles compose the composite dipole to achieve a wideband operation. By utilizing the composite dipole, four resonances can be simultaneously excited and manipulated to increase the bandwidth. A prototype is manufactured to validate the method. The dimensions of the antenna are just 0.62λ0 × 0.62λ0 × 0.03λ0 (λ0 is the free-space wavelength at center frequency). The measured results show that the presented antenna has a impedance bandwidth of 58.6% (1.63–2.98 GHz) for VSWR ≤2. The gain variations are less than 0.6 dB at the azimuth plane in the operating band. Meanwhile, the cross-polarization is less than 20 dB and the peak gain reaches 1.7 dBi among in the band. These advantages of the antenna make it suitable for 4G mobile communication applications.