Multiband/wideband Dual-polarized Omnidirectional Antennas

Multiband/wideband antennas are suitable for the miniaturization of communication equipment where one antenna can be applied for different cases.As an application of polarization diversity technology,dual-polarized antennas can effectively resist multipath fading and improve the spectrum utilization,which can also increase the capacity of communication systems.Omnidirectional antennas can radiate and receive signals in all directions of the horizontal plane,which makes them be widely used in broadcasting and wireless communications,such as mobile communications and WLAN(Wireless Local Area Network).Note that antennas designed specifically for applications on high-speed vehicles/aircrafts are required to have miniaturized simple structure,especially with low-profile or narrow cross section so that they can be packaged in a radome with a streamlined shape to alleviate wind resistance.Most omnidirectional antennas proposed previously are not mountable on high-speed vehicles/aircrafts.Novel multiband/wideband dual-polarized omnidirectional antennas are proposed in this paper which are suitable for mounting on high-speed vehicles/aircrafts.The main contributions of this work are summarized as follows:1.A dual-band dual-polarized(DP)omnidirectional antenna for the 2.4 GHz ISM and 5 GHz Wi Fi/WLAN/ISM applications is proposed,which includes a slotted metal cavity and two metal feeding lines.The horizontally polarized(HP)element consists of a vertical slot backed with a metal box,which is excited by a tapered feeding patch with a U-slit for dual-band operation.The vertically polarized(VP)element is composed of two horizontal slots excited by a two-branch feedline.The dual-band DP omnidirectional antenna achieves an overlapped impedance bandwidth of 7%(2.34-2.5 GHz)for the lower band and 15.5%(5.06-5.91 GHz)for the upper band with an isolation of higher than 35 d B.Good omnidirectional radiations are observed for the dual frequency bands.2.A new tri-band DP omnidirectional antenna is proposed based on the dual-band DP omnidirectional antenna.The proposed antenna is composed of a metal cuboid with a vertical slot for HP and a rectangular back metal cavity with two folded horizontal slots for VP.The metal HP feedline coupling to the vertical slot consists of three stubs: a rectangular patch,a tapered strip,and an L-shaped stub.Two slots are embedded along the center line of the feedline.Two folded horizontal slots are excited by the metal VP feedline,which consists of a Y-shaped patch with two branches of different lengths,an L-shaped patch,and three rectangular patches of different sizes.Experimental results show that the tri-band DP antenna covers the Chinese Unmanned Aircraft System bands(840.5-845 MHz,1430-1444 MHz and 2408-2440 MHz)with reflection coefficients <-10 d B and isolation > 35 d B.Good omnidirectional radiation patterns are observed for both HP and VP.3.A wideband DP omnidirectional antenna with high-isolation for 5G applications is proposed,which includes a slotted metal cavity and two metal feeding line.The HP element consists of a vertical slot backed with a horn-shaped metal box,which is excited by a tapered feeding patch for wideband operation.The VP element is composed of a horizontal slot excited by a “?”-shaped feedline.The wideband DP omnidirectional antenna achieves an overlapped impedance bandwidth of 52.8%(3.01-5.17 GHz)with an isolation of higher than 41 d B.Good omnidirectional radiations are observed in the operating bands.