Novel Multiband/Broadband Horizontally Polarized Omnidirectional Antennas

Omnidirectional antennas are widely used for radio broadcasting, satellite communication, space vehicles and applications in wireless communications. It has been predicted that a communication system with horizontally polarized antennas may obtain up to 10 dB diversity gain than a communication system with vertically polarized antennas in the urban or indoor wireless environment. Furthermore, multiband/broadband antennas are good for miniaturization of communication equipment where one antenna can be used for different purposes. Moreover, some of existing horizontally polarized omnidirectional antennas(HPOAs) are not suitable for high-speed vehicles/aircraft. Novel multiband/broadband HPOAs are proposed in this paper. Besides, these HPOAs are suitable for high-speed vehicles/aircraft. The HPOAs are made up of a metallic cavity and a bent feedline. In this paper, we focus on the HPOAs to achieve different performances by shaping the cavity and the feedline.A dual-band HPOA is proposed first based on a vertical slot antenna. The proposed antenna includes a metallic cuboid with a vertical slot. A bent strip with a U-shaped slot is utilized to excite the vertical slot. A brief description for the operating principle of the antenna has been given in this article. The reason for the antenna to cover the frequency of WiFi and the influences of the critical parameters on the return loss(RL) are investigated. Experimental results show that the dual-band HPOA has 10-dB RL bandwidths of 8.8%(2.37-2.59 GHz) for the lower band and 21.5%(4.85-6.02 GHz) for the upper band, respectively. Good omnidirectional radiation patterns are obtained for the dual-band HPOA.On the basis of the dual-and HPOA, a broadband HPOA is then developed by controlling the frequency ratio of the two resonant bands and utilizing the broadband performance of the horn radiation cavity. The antenna is made up of a metallic horn cavity and a bent feedline. The operating principle of the antenna is the same as the dual-band HPOA. The antenna can achieve a broadband performance, and the influences of the critical parameters on the RL are demonstrated. Experimental results show a bandwidth of about 50.2%(1.67-2.79 GHz) for RL>10 dB. Good omnidirectional radiation patterns are also obtained for the broadband HPOA.A compact tri-band HPOA is finally proposed based on the dual-band HPOA by shaping it’s feeding line. The feedline consists of two stubs: an L-shaped stub and a folded stub. In order to increase the frequency bandwidth of the lower band, two slots are embedded along the center line of the feedline. The paper analyzes the tri-band model formed from the dual-band model in detail. At the same time, the influences of the critical parameter on the RL are also investigated. Experimental results show that the tri-band HPOA covers the Chinese Unmanned Aircraft System bands(840.5-845 MHz, 1430-1444 MHz and 2408-2440 MHz). Good omnidirectional radiation patterns are also observed.