Research On Wideband Omnidirectional Antenna And Tightly Coupled Antenna Array

Omnidirectional antenna has been widely used in wireless communication system.To overcome the increasing challenges of broadband and intellectualization in wireless communication system,some special performances such as broadband,high gain,and miniaturization are required for omnidirectional antenna.In addition,the tightly coupled array has attracted much attention due to its advantages of ultra-wideband,wide scanning angle,and ultra-low profile.However,the rapid optimization design is still unsolved for the tightly coupled array.In this paper,the design are mainly concerned with the techniques of widening the bandwidth of the vertically polarized,horizontally polarized and circularly polarized omnidirectional antennas,as well as the fast optimization of the tightly coupled array.At last,the method that extending applied realms of the tightly coupled technique has been discussed.The author’s major works and contributions are summarized as follows: 1.The basic principles and characteristics of the conventional dipole and monopole antennas are studied for the requirements of vertically polarized omnidirectional antenna.The method of realizing broadband,low profile,and high gain of the vertically polarized omnidirectional antenna is studied.1)A quadripod kettle monopole antenna is applied as the design prototype along with T-bar,tapered gradient structure,and loading technique,achieving good performance of broadband and low profile.2)A broadband and high-gain vertically polarized omnidirectional antenna is designed based on angular reflector and longitudinal array composed by conventional dipole antenna.Theoretical analysis and experimental verification are performed to justify the rationality of the design.3)Another broadband and high-gain vertically polarized omnidirectional antenna is designed with double-sided printed dipole arranged alternately in the axial direction and a broadband Marchand balun.Good properties are achieved by the introduction of the right reflectors and the integrated design of the feeding network and the elements.2.The wideband horizontally polarized omnidirectional antennas are studied.1)The multi-resonant structure for extending working bandwidth is explored.A broadband and miniaturized horizontally polarized omnidirectional antenna operating in the 4G LTE band is designed in the form of double printed composite dipole with parallel transmission lines.The realization of multi-resonances and miniaturization are emphatically analysed.2)Another horizontally polarized omnidirectional antenna with broadband and miniaturization properties operated in the VHF band is proposed.The miniaturization of the X-dipole is realized by using the terminal shorting technique,and its broad band is achieved by combining the design of parallel transmission line and broadband balun.The influences of the dipole structure and the feeding network on the antenna bandwidth and radiation characteristics are analysed in detail in the paper.3.The paper is also dedicated to the design of the broadband circularly polarized omnidirectional antenna.1)A circularly polarized omnidirectional antenna with wide axial ratio bandwidth for WLAN communication is designed.The omnidirectional circularly polarized performance is realized in the form of monopole and arc-shaped strips.The broad axial ratio bandwidth is achieved by coupled feeding.2)In order to extend the impedance bandwidth of the above circularly-polarized omnidirectional antenna,another coupled resonant branch is applied on the aforementioned structure,achieving two resonances and broad bandwidth successfully.Moreover,the effects on the radiation performance of two different resonant paths are analysed.4.Ultra-wideband tight coupling array is also studied.1)Through the array equivalent circuit and the full-wave EM simulation with infinite periodic boundary,the initial structure of the array element is design and its property is analysed in different scanning planes.2)And then the adaptive differential evolution algorithm combined with the Gaussian process is used to quickly accelerate the design of the wideband array element,which greatly improves the design efficiency of the tight coupled antenna array.3)The truncation effect has been studied,and a 3×8 ultra-wideband tightly coupled phased array antenna is achieved,manufactured and measured.The measured results verify the rationality and effectiveness of the design process.5.The implementation of the tightly coupled technique on circularly polarized antenna is investigated.Based on the principle of tight coupling,two directional broadband circularly-polarized antennas are designed by using the end-coupled L-shaped probes and printed dipoles with broadband impedance transforming networks and sequential feeding networks.The two antennas have wide bands,high gain and compact structure,which greatly extend applied realms of the tightly coupled technique.