Study Of Radio Electromagnetics Vortex Generation And Application Research

Recently,radio vortex has been a popular research topic in microwave regime and attracts increasing attention.Unlike the planar wave,the vortex has a typical helical wavefront,carrying orbital angular momentum(OAM).Benefiting from the orthogonality of OAM modes and the rich phase response,radio vortex creates a perspective view for the OAM-based communication and radar system.By employing the orthogonalities of OAM modes,the speed of communication system can be improved without extra cost of spectrum.And the different phases in different azimuth directions entitle radar a super-resolution capacity,which is beneficial for obtaining informative property of the target.For the existing problems in the OAM-based communication and radar systems,this dissertation explores relevant technologies theoretically and demonstrates the solution,which are then verified by the extensive simulations and measurement results.Regarding the defective elements in a uniform circular array(UCA),it will lead the UCA to an imperfect UCA(IUCA),which will pose influence on the production of OAM mode.To evaluate the influence,we derive the relevant formulations,which imply that the distortion of OAM mode is due to the pollution of OAM orthogonal property by other OAM modes.To retain the orthogonal property,orthogonal matching pursuit(OMP)algorithm,the convex tool(CVX)and the analytical solution are demonstrated to design the feeding network.The simulation results indicate the validity of the formulation result and the effectiveness of the proposed feeding method.To solve the misalignment problem between the transmitter and the receiver,a UCA-based radio vortex scanning or OAM scanning is introduced to realign the vortex.To evaluate the performance of the proposed technology,we have studied the influence of the scanning elevation and azimuth angles on the OAM mode quality.Subsequently,a UCA with microstrip feeding network is designed and tested to verify the effectiveness of the proposed method.The radiation pattern and transmission performance is also evaluated,which suggests that the radio vortex scanning is feasible to solve the misalignment problem for small elevation angle.The conventional algorithms used in vortex radar such as fast fourier transform(FFT)and back projection,have a low resolution.To further improve the resolution ability of vortex-based radar,multiple signal classification(MUSIC)algorithm is illustrated.For the highly correlated matrix of echo signals,front spatial smoothing is employed to recover the full rank.The simulation results indicate that the proposed algorithm has a higher resolution and can work in lower signal to noise ratio(SNR)environment,with more robust performance.The wide angle of the main lobe of the vortex antenna would decrease the distance of the OAM-based communication,which therefore requires a narrow beam pattern.The grooves in a planar plate can help decrease the angel of main lobe.However those grooves are based on the metallic material,which is not suitable for compact applications.Hence,the development of light planar groove structure is in demand.We have proposed substrate integrated waveguide(SIW)-based grooves to sharpen the beam pattern,which is helpful for the future narrow beam vortex designs.The proposed single-layer SIW groove method decreases the design complexity with better performance.Study of tapered microstrip line and the ground coplanar waveguide(GCPW)transitions is made to compare the performance,with the result suggesting that the GCPW transition can achieve a better gain enhancement and a wider bandwidth,with the lower cross polarization level.The study of radio vortex in our dissertation provides theoretical and experimental support for the future researches,which will promote the development of the relevant topics.