Simulation Study Of Wide Axial-Ratio Beamwidth For Circular Microstrip Patch Antenna

With the rapid development of modern communication technology,the antenna function are more diverse,and the antenna index requirements are more stringent in mobile communication system.Microstrip antennas are widely used in modern communication systems because of their many advantages such as low profile,light weight and low cost.Circularly polarized antennas own anti-multipath interference and anti-Faraday rotation performance,so they are often used as transmitting and receiving antennas in satellite communication systems.In order to receive signals in a wider area on the ground and ensure the normal operation of mobile communications,the receiving antenna is required to maintain good circular polarization characteristics in a wide angle range,that is to say,the receiving antenna is required to possess wide axis ratio beam characteristics.In the light of achieving the requirements for microstrip antenna in satellite communication system,the current research status of microstrip antennas are understood by consulting relevant documents which are wide band or wide axial-ratio beam microstrip antenna,along with wide band and wide axial-ratio beam microstrip antenna.Then the methods are summarized how to expand microstrip antenna's bandwidth and axis-ratio beamwidth.In chapter 2,the cavity theory of microstrip antennas is introduced detailly,including rectangular microstrip antenna,circular microstrip antenna,annular microstrip antenna and pin-loaded circular microstrip antenna.The cavity theory of microstrip antennas provides theoretical support for the follow-up simulation and research of this paper.In Chapter 3,single layer circular microstrip antenna is researched.The result between simulation in HFSS and calculation with the cavity theory in Matlab are almost identical.The technique of loading shorting-pins on circular patches is adopted to extend the axial ratio beamwidth by introducing mixed mode.The antenna is fed by double points to realize circle polarization.The researches include three aspects,dielectric constant of substrate,diameter of patch,the location and number of shorting-pins.Finally,the result is that the relative impedance bandwidth of the antenna is 0.4%,and the 3d B axial ratio beamwidth is more than 160 degrees.In Chapter 4,on the basis of broadening the beam width of axial ratio,a new resonant point is introduced by adding parasitic patch in the vertical direction.The purpose of expanding impedance bandwidth is achieved by adjusting the radius of the radiation patch and parasitic patch to make the two resonant points closely.It is found that there are some restrictions between the impedance bandwidth and the axial ratio beam width of the antenna.Under the optimization of HFSS software,the results are obtained which is considered both the bandwidth and the axial ratio beam width.The relative impedance bandwidth of the antenna is 5.3%,and the 3d B axial ratio beam width is wider than 140 degrees.The antenna feeds in this paper are doubly fed.In order to meet the engineering requirements,the feeding network of the antenna is designed in this paper.According to the requirement of the antenna for bandwidth and axial ratio beam width,the branch line coupler is designed and optimized.Finally,the antenna with the branch line coupler is optimized.A circularly polarized microstrip antenna is realized which possesses wide axial ratio beam width and wide bandwidth characteristics.