Research And Design Of S-band Omnidirectional Circularly Polarized Antenna

Antenna as an matching device of circuit and free space, whose performancedirectly affects the performance of the entire wireless system plays a pivotal role atthe signal reception or transmission, and is therefore an important part of the wholesystem indispensable. With the rapid development of modern wireless communicationtechnology, the requirement of the antenna performance becomes higher and higher.At the present time antenna with simple linear polarization would be difficult to meetthe various needs in modern communication system. In this situation, a wide range ofconcerns about circularly polarized antenna is increasing. Omnidirectional circularlypolarized antenna not only radiate circularly polarized electromagnetic waves, butalso generate omnidirectional directional pattern, that is, within the radiation azimuthplane is omnidirectional. And because of its predominances, the omni-directionalcircularly polarized antenna is widely used in communication, telemetry, radar,electronic reconnaissance and interference, and so on.This dissertation mainly searches the design and realization of theomni-directional circularly polarized antenna. Monopole antenna radiatesomnidirectional vertically polarized wave, by loading the parasitic units outside of themonopole antenna, the single linearly polarized wave can be decomposed into twolinearly polarized wave component which have equal amplitude, orthogonalpolarization,90°phase difference, these two components in the far field synthesis forcircularly polarized waves, to achieve an omnidirectional circularly polarized. Usingelectromagnetic simulation software Ansoft HFSS, the design of compact structure isoptimized. An omnidirectional circularly polarized sleeve monopole antenna withsimple structure, easy fabricated and wide-band is carried out. Finally the antennas areprocessed and tested. The main research results are as follows.Firstly, the basic theory of omnidirectional circularly polarized antenna areexpounded, so as the advantages and development of omni-directional circularlypolarized antenna. The current research methods and the future trends of the circularlypolarized omnidirectional antenna are summarized and studied. The basic principles and characteristics of the monopole antenna are introduced, the basic theory andvariations of sleeve antenna are discussed, the basic theory and implementation ofcircular polarization are analyzed.Secondly, based on the summary and the absorption of research results andlessons learned from others, we propose a new omnidirectional circularly polarizedantenna structure. The basic principle of the design process and the structure isanalyzed.The relationships between the antenna structure parameters and the variousaspects of the performance are qualitative analyzed detailedly. The main sleevemonopole radiating element has been improved, two improved circularly polarizedomnidirectional antenna are proposed.Finally, in order to verify the reasonableness of the design of the antenna, wemanufacture and measure the antenna. The measured results have a good agreementwith the simulated resulted. The half-space radiation characteristics, gain andradiation diameter size were all satisfactory, The antenna whose VSWR is below2was easy to integrate with application-specific circuit. This rod antenna has simplestructure and easy fabricated, suitable for a lot of areas such as military and civiliancommunications.