Research On The Design Of Broadband Unidirectional Circularly Polarized Antenna

As the important parts of wireless communication systems,antennas have undergone serval waves of technological revolutions in the upgrades of each generations of wireless systems,and the key technologies of antennas are constantly being developed.In particular,broadband circularly polarized antennas with directional radiation characteristics have received extensive attention from scholars,due to their strong adaptability and wide application scenarios.This thesis systematically summarizes the current development of broadband directional circularly polarized antennas.And for sloving the key issues of broadband multi-polarization,low profile,high aperture efficiency,etc.Serval types of broadband unidirectional circularly polarized antennas working in different frequency bands,applied in different fields were proposed.The main contributions of this thesis are listed as follows:1.Aiming at the issues of single polarization mode and limited bandwidth of classical magnetoelectric dipole(ME Dipole)antennas,a ME dipole with the characteristics of dual-circular polarization is presented.A new type of cross-feeding structure is designed to ensure the good impedance matching characteristics of the antenna.At the same time,the proposed feeding structure can excite polarization currents with equal amplitude and orthogonal phases.By using the unidirectional radiation characteristics of the ME dipole,so as to achieve broadband works with dual circular polarization.Measured results show that the proposed antenna has stable dual-CP radiation patterns within the operation band.The overlapped bandwidth is 53.2% for RHCP from 1.71 GHz to 2.95 GHz and 62% for LHCP from 1.7 GHz to 3.25 GHz,respectively.Due to the broadband dual-CP characteristic of the proposed antenna,it has good prospects of engineering applications.2.Aiming at the problems of narrow band and high profile of traditional unidirectional cross-dipole antenna,a metasurface-loaded broadband low-profile directional crossdipole antenna is designed.First,parasitic elements are added to the traditional crossdipole radiation structure to optimize its current distribution and broaden its frequency band.Then,based on the two-dimensional Electronmagnetic Band Gap(EBG)structure,a novel broadband Artificial Magnetic Conductor(AMC)unit was proposed.By combining the AMC unit as the reflector of the radiation unit,using its zero-phase reflection characteristic,the proposed antenna realized the characteristics of unidirectional radiation while ensuring low-profile.The proposed antenna has a wide operating band of 23.8%,the realized peak gain in the main beam range can maintain between 6.5-7.7 d Bic in the whole operating band.This antenna has huge application potential in the fields of airborne or other modern wireless systems.3.To solove the problems of low gain and limited aperture efficiency and narrow operating band of traditional microstrip patch antennas,a broadband meta-surface loading and high gain low-profile CP patch antenna based on multi-layer structure is presented.The antenna works in the Ku-band,and the overall structure is simple and easy to be integrated.Different from the traditional metasurface loading structures,the antenna uses dielectric loading layers to replace the original air loading layers.And the antenna adopts the multi-layer technology,each layer of dielectric boards is bonded by a cured sheet,which greatly reduces the assembly difficulty of the antenna.Measured results show that the proposed antenna realized a operating bandwidth of 21.9%,and the realized gain in whole band is maintained at about 9.5 d Bic,which achieves excellent high-gain broadband unidirectional circularly polarized radiation characteristics.