Study On Broadband And Multiband Circularly Polarized Antennas

With the rapid development of modern wireless communication technology,the communication equipment with low function,large size and low application range can not meet the strong demand of the majority of users.As an important part of the wireless communication system,the antenna usually plays the role of receiving and transmitting signals.Its radiation performance will directly affect the communication quality and service efficiency of the whole system.Compared with traditional linear polarization antenna,circular polarized antenna has strong advantages in eliminating multipath interference and signal weakness.In addition,scarce spectrum resources and increasingly crowded channel capacity require antennas to be compatible with multiple frequencies.Therefore,the circular polarization antenna with broadband/multi-band is the research direction of this paper.The main research contents of this paper are as follows: 1.The thesis makes relevant statements on the research significance and background of the topic,explains some circular polarization antennas related theory,introduced the research status of broadband/multiband circular polarized antennas at home and abroad,and then expressed the necessity of this research.2.Two broadband circularly polarized slot antennas are proposed in this paper.One is an ultra-wideband circularly polarized monopole antenna fed by a coplanar waveguide.By embedding an inverted L-shaped and a rectangular metal strip into both sides of the floor,ultra-wideband circularly polarized radiation can be achieved.The measured results show that the operating bandwidth of the antenna can cover the UWB communication band,and the axial ratio bandwidth reaches 61.3%(3.42-6.44 GHz).There also has an improved broadband slot circular polarized antenna.The metal feedline and slot-shaped metal patch are printed on both sides of the substrate.By arranging rectangular metal branches into the trench,the impedance and axial ratio bandwidths can reach 102% and 54.6%,respectively.3.The thesis proposes a dual-band circularly polarized monopole antenna suitable for some partial agreement bands of the Wireless Local Area Network(WLAN)and Worldwide Interoperability for Microwave Access(WiMaX).By embedding a "T" shaped and an inverted "L" shaped metal strip into the inside of an arc-shaped antenna,dual-band operation and circular polarization radiation are realized.This paper also analyzes the principle of dual-band circular polarized radiation of the antenna from the evolution of this antenna structure,parameter analysis and current distribution.Finally,processing and testing were performed based on the optimized dimensions.Compared with the reference,the results also show that the designed dual-band circularly polarized monopole antenna has some certain advantages.4.This thesis introduces the basic principle of electromagnetic dipole antenna,and analyzes the advantages of using it as a basis to design a broadband circular polarization antenna.The circularly polarized radiation can be achieved through a pair of sickle-shaped metal plates that are 180° rotationally symmetric along the z-axis.The operating and axial ratio bandwidths of this antenna are 97.2% and 66.2%,respectively.The directionality and symmetry of the radiation pattern are relatively well,and the gain of the antenna is kept at a high average.