Research On Dual-polarized Omnidirectional Antenna

Omnidirectional antenna has been widely used in wireless local area networks and other fields due to its feature of 360° full coverage on the horizontal plane.Dual-polarized antenna has the advantages of increasing the channel capacity,improving the spectrum utilization and resisting the multipath fading.In this thesis,horizontally/vertically polarized omnidirectional antenna and dual-polarized omnidirectional antenna are studied systematically.Based on the traditional slot antenna,three types of omnidirectional antennas are proposed to achieve miniaturization and multiband.Firstly,two kinds of dual-band horizontally polarized omnidirectional antennas based on three-dimensional radiation slot are proposed.In order to realize the miniaturization of the antenna,three-dimensional radiation slot is adopted to reduce the height of vertical slot.A folded stepped patch is employed to feed the three-dimensional slot to realize dual-band resonance.The working bandwidth of the antenna is extended by offsetting the feeding structure from the center of vertical direction and adding parasitic patches,respectively.Compared with the offset feeding antenna,the parasitic feeding antenna has much lower cross polarization level in the high frequency band.The dimensions of both antennas are 30mm×25mm×10mm.Experimental results show that the-10 d B impedance bandwidths of the two antennas are 2.38-2.55 GHz,4.7-6.1GHz and 2.38-2.51 GHz,4.8-5.9GHz,respectively,and the gain variation on the horizontal plane is less than 6 d B.Secondly,two kinds of dual-band vertically polarized omnidirectional antennas based on horizontal folded slot are proposed.The first antenna consists of a rectangular metal cavity with a horizontal folded slot and a multi-node feedline.On this basis,for the purpose of easy fabricated,three sides of the rectangular where the horizontal folded slot is located are reserved,and the feeding branch is simplified to form an open cavity dual-band vertical polarized antenna.The dimensions of both antennas are 30mm×25mm×10mm.Experimental results show that the-10 d B impedance bandwidths of the two antennas are 2.39-2.5GHz,5-5.85 GHz,and 2.4-2.5GHz,4.8-6.3GHz,respectively,and the gain variation on the horizontal plane is less than 6 d B.Finally,two kinds of dual-band dual-polarized omnidirectional antennas are proposed based on the antennas mentioned above.They are composed of the open cavity dual-band vertically polarized omnidirectional antenna and two kinds of dual-band horizontally polarized omnidirectional antennas.The two dual-band dual-polarized omnidirectional antennas can cover the WIFI dual-band with the volume of 30mm×50mm×10mm.High isolation and good omnidirectionality are observed in the operating bands.