Research And Design Of Broadband And Wide Beam Circularly Polarized Antenna

With the rapid development of wireless communication technology,Systems for wireless communication technology have increasingly high requirements for antennas.Especially wide beam antennas with circular polarization play a vital role in short-range and wide-range wireless communications.Wide beam antennas can be broadly classified into two categories according to their radiation,omnidirectional antennas that can achieve 360° omnidirectional radiation in azimuth,and hemispherical beam antennas that can radiate uniformly throughout the upper half of the airspace.Omnidirectional antennas can be used in indoor wireless communication,on-board communication,and mobile terminal.If combined with circular polarization technology,they can combat multipath fading,reduce polarization loss and have strong anti-jamming capacity.Circularly polarized hemispherical antennas are now widely used in satellite communications and satellite navigation.These antennas not only cover the entire upper half of the airspace,but also have an almost uniform distribution of the radiated power.In other words,the radiation direction diagram of a hemispherical antenna should be as close to a "flat top" beam as possible.This paper firstly introduces the background and significance of the research on wide-beam circularly polarized antennas,and studies and analyses the radiation principle of circularly polarized antennas;secondly,it focuses on the design methods and wide-band techniques of omnidirectional circularly polarized antennas and hemispherical circularly polarized antennas and process some antennas to verify the accuracy of the theory.The main work of this paper is as follows:1.A theoretical analysis and comparison of large-loop and small-loop antennas is carried out.Based on this,a low-profile wideband horizontally polarized omnidirectional antenna was designed by splitting the large-loop to achieve the same direction distribution of current.The impedance bandwidth of |S11| <-10 d B is27.4%,the azimuth non-circularity is less than 2.7dB,and the average gain is about1.4d Bi.The antenna can be used either as a stand-alone antenna or as an important unit in the composition of an omnidirectional circularly polarized antenna.2.The loop antenna + monopole model is analyzed and a broadband low-profile omnidirectional circularly polarized antenna is designed by adjusting the amplitude value of its electric field component,which consists mainly of a vertically polarized monopole and a horizontally polarized bimetallic ring.The impedance bandwidth of antenna |S11| <-10 d B is 36.4%,but the bandwidth with axial ratio less than 3d B is only 18.8%,and its axial ratio beam width is narrow.To address the shortcomings of the first omnidirectional circularly polarized antenna described above,an improved omnidirectional circularly polarized antenna has been designed using a combination of a loop antenna and a short-circuited metal column.The antenna satisfies an axial ratio of less than 3d B for almost the entire pitch plane and has an impedance bandwidth and axial ratio bandwidth of more than 20%.3.Based on the theory of multimode synthesis,a wide beam circularly polarized hemispherical antenna has been designed using the idea of a multimode radiator loaded with a circular polarizer.The antenna operates in Ku-band with a 3d B power beamwidth of 185° and a 3d B axial ratio beamwidth of 90° and can achieve "flat top" radiation within ±70°.4.To address the demerit of the first hemispherical circularly polarized antenna described above,the replacement of the multimode radiator with a dielectric horn resulted in a significant improvement in the performance of the antenna.Simulation results show that the antenna has a 3d B power beamwidth of 172° at the centre frequency,a beamwidth of 182° for axial ratios less than 3d B,and the working bandwidth is widened to 10%.