Study Of High Directivity Planar Endfire Circularly Polarized Antennas

Circularly polarized waves are widely used in wearable antennas,satellite navigation,and radio frequency identification systems(RFID)because they can suppress multipath loss and polarization mismatch.For circularly polarized antennas,the directivity in the endfire direction is an important performance.In order to obtain higher directivity,the conventional circularly polarized antennas often use more complicated non-planar structures or additional dielectric lenses.They usually have a complex antenna structure or a large volume.Therefore,how to design a circularly polarized antenna which has the advantages of high directivity,simple structure and low profile,and has an endfire beam parallel to the plane direction of the antenna has been a challenging problem.This thesis focuses on solving the problems of low directivity and large profile in circularly polarized antennas.On the basis of simple structure,a new design idea of high directional planar circularly polarized antenna – a V-shaped dipole antenna operating in higher-order modes is proposed,the main research of this thesis includes:1.This topic aims to design a planar end-fired circularly polarized antenna with high directivity and thus conduct a series of studies.Firstly,the mechanism of producing high directivity is explored.Then the design idea of the target circularly polarized antenna is studied.Finally,the original antenna structure,ie rectangular planar magnetic dipole and V-shaped electric dipole,are obtained based on theoretical analysis and working principle.2.Under the premise of maintaining the high directivity of the antenna,the miniaturized antenna is further designed by using the off-centered distance of the V-shaped dipole instead of the original 1/4 wavelength phase conversion line to generate an appropriate phase difference and reduce the cross-sectional area of the antenna.The main decision parameters of the antenna directivity are studied,and the correctness is verified by Zeland's IE3 D simulation software.The optimal parameters are determined after parameter analysis,then a hand-made antenna sample centering at 2.6 GHz are produced.3.The Agilent's 8720 ET vector network analyzer and the Satimo Starlab near-field antenna test system were used to verify the actual radiation performance such as impedance characteristics,radiation pattern and axial ratio of the antenna samples.After the measurement of the antenna samples,the results of theoretical calculations,simulations and actual measurements were found in good agreement,which further proves the correctness of the design ideas of this topic.The operating frequency of the antenna in this study is 2-3 GHz,that is,the Bluetooth and wifi bands.The actual measured impedance bandwidth of the antenna sample is 2.56-2.69 GHz,and the circularly polarized wave covers 2.12 GHz-2.77 GHz,that is 650 MHz totally.The impedance bandwidth is covered by the circular polarization bandwidth totally,and the measured gain is up to 6.1dBic under the premise of simple structure and small volume,so the antenna developed in this thesis can be applied to the design of base station antennas in areas with large population density(such as schools,communities and supermarkets).It also meets the requirements for industrial science medical wearable antennas and RFID systems.