Research On Dual-polarized Omnidirectional Antenna

Omni-directional antenna has the radiation performance of 360° coverage over the horizontal plane,and is widely used in the communication fields such as mobile communication,wireless local area network and navigation system.Circularly polarized antenna has its unique characteristics in practical engineering applications.Therefore,this thesis does a systematic research on the omni-directional circularly polarized antenna which possesses the omni-directional radiation characteristics and the circularly polarized radiation characteristics,and proposes two kinds of horizontal omni-directional circularly polarized antennas.Firstly,a single-band omni-directional circularly polarized antenna is designed.The designing method is to use the monopole antenna with omni-directional vertical polarization radiation characteristics,by loading parasitic radiation elements to change the polarization characteristics of radiated electromagnetic waves,so as to achieve omni-directional circularly polarized radiation.The form of parasitic units is four groups of Y-shaped spiral patches uniformly placed around the monopole.The size of the antenna is35mm×35mm×31mm.Measured results show that the-10 d B impedance bandwidth of the antenna is 2.33 GHz-2.44 GHz,the relative bandwidth is 4.61%,the 3d B axial ratio bandwidth is 2.38 GHz-2.42 GHz,and the relative bandwidth is 1.67%.The maximum gain of left-handed circular polarization and right-handed circular polarization are 0.89 d Bi and-21 d Bi,.The axial ratio range of the antenna is 1.4d B-2.4d B in the horizontal plane,while the out-of-roundness is below 0.5d B.This omni-directional circularly polarized antenna has good omni-directional performance and circularly polarized performance.Secondly,a dual-band horizontal omni-directional circularly polarized antenna is designed,composed of the metal via added on the substrate,the ground and the parasitic branches loaded on the top patch.The metal via is equivalent to a monopole antenna,which radiates vertical omni-polarized waves,and the parasitic ring branches are equivalent to a ring antenna,which radiates horizontal omni-directional polarized waves,to form the dual-band radiation of omni-directional circularly polarized antennas.Therefore,the design principle is to synthesize omnidirectional circularly polarized waves in the far field by feeding multiple independent linearly polarized antennas at the same time.The size of the antenna is 50mm×50mm×3mm.Measured results show that in the lower 2.4 GHz band,the-10 d B impedance bandwidth of the antenna is 2.38 GHz 2.43 GHz,the relative bandwidth is 2.1%,the 3d B axial ratio bandwidth is 2.36 GHz-2.44 GHz,and the relative bandwidth is 3.3%.The maximum gain of right-handed circular polarization and left-handed circular polarization are 0.4 d Bi and-20 d Bi,while the out-of-roundness of the antenna is 1.9 d Bi,which realizes omni-directional right-handed circular polarization radiation.In the higher5.8 GHz band,the-10 d B impedance bandwidth of the antenna is 5.72 GHz-5.88 GHz,the relative bandwidth is 2.7%,the 3d B axial ratio bandwidth is 5.75 GHz-5.88 GHz,and the relative bandwidth is 1.7%.The maximum gain of left-handed circular polarization and right-handed circular polarization are 4.2 d Bi and-30 d Bi,,while the out-of-roundness of the antenna is 1 d Bi,which realizes omni-directional left-handed circular polarization radiation.This dual-band omni-directional circular polarization antenna has good omnidirectional performance and circular polarization performance in two working impedance bands.