Vertical Plane Radiation Property Control Of Low Profile Omnidirectional Antennas

Wireless communication is one of the fastest and most convenient ways of communication.As an essential component of the wireless communication system,the antenna has become the focus of research in the field of radio.According to the radiation pattern,antennas can be divided into omnidirectional antennas and directional antennas.The omnidirectional antennas have the radiation characteristics of uniform radiation on the horizontal planes,so they can be widely used in the fields of satellite communication,mobile communication,point-to-multipoint communication and space vehicles.Reducing the half-power beamwidth in the vertical planes can increase the antenna gain.Different from the commonly used the method of arraying in the vertical planes,this paper will use the horizontal parasitic elements to achieve this goal.The main research contents include:Chapter one introduces the research background of omnidirectional antennas and summarizes the research progress of vertically polarized omnidirectional antennas,horizontally polarized omnidirectional antennas and circularly polarized omnidirectional antennas.In addition,this chapter also gives the main research content and structural arrangements of this paper.Chapter two expounds the basic theory and analysis methods involved in the research of this paper.It mainly includes:(1)design specifications of omnidirectional antennas,such as radiation pattern,gain,polarization characteristics and bandwidth;(2)omnidirectional modes of circular patch antennas and two kinds of miniaturized circular patch antennas;(3)radiation field superposition principle and principle of pattern multiplication;(4)geometrical theory of diffraction and calculation method of total radiation field in the presence of the scatterer.Chapter three designs the theoretical model of reducing the beamwidth in the vertical planes of the omnidirectional antennas based on the radiation field superposition principle.Based on the theoretical model,low profile and narrow beam omnidirectional antennas with the maximum radiation direction in the horizontal plane are designed.In this chapter,firstly,a circular patch antenna with tortuous I-shaped parasitic elements is designed.Compared with the reference antenna without loading,the loading antenna can reduce the half-power beamwidth and improve the antenna gain without increasing the height of the antenna profile.However,there are deviations between the simulation and test results of the antenna,so we improve the design of the antenna and propose a circular patch antenna with tortuous I-shaped parasitic elements and multiple shorting pins.Chapter four mainly studies the low profile and narrow beam omnidirectional circular patch antennas with elevation angles.This chapter first builds the model of reducing the beamwidth of an omnidirectional antenna with small ground based on the geometric theory of diffraction.And the narrow beam antenna is designed using this theoretical model.Compared with the reference antenna,the narrow beam antenna reduces the half-power beamwidth of the antenna to about 55 degrees while ensuring that the horizontal and vertical dimensions are not increased.In addition,this chapter also discusses the method of reducing the antenna beamwidth when the radius of the ground is large.This method also can reduce the antenna half-power beamwidth,but the reduction effect is not obvious,only about 5 degrees.Chapter five summarizes the main research content of this paper and shows the shortcomings of the current research work and makes prediction about the research work in the future.