The Generation Of The Vortex Electromagnetic Waves And Its Application In Imaging Region

In recent years,the economy and science technology are developing rapidly,and the process of informatization is growing faster and faster.As the information carriers,the electromagnetic(EM)wave and its applications in the related imaging regoin have brought great convenience to people 's production and life,but they still cannot meet people's increasing demands.As a new physical quantity of the EM wave,orbital angular momentum(OAM)provides a new phase degree of freedom for EM wave and has attracted a lot of attentions from the related scholars.Vortex EM waves is one of the EM waves which carry OAM modes and the number of the OAM modes is infinite in theory.The different OAM modes are orthogonal to each other and propagate independently in space to span an infinitely-dimensional Hilbert space.Thus,vortex EM wave is expected to be used in imaging systems to improve the imaging resolution.The generation of vortex EM wave is the premise of its application.Based on the central proposition of the generation of vortex EM wave and its application in the imaging region,we focus on the reaserches of generating broadband multi-OAM mode vortex EM wave,generating underwater vortex EM wave,and EM vortex imaging algorithm.Our main work and its innovations are summarized as follows:1.Based on the application of vortex EM wave,the requirements of antenna bandwidth and the number of OAM modes are analyzed.Then,we propose the N-arm Archimedean spiral antenna structure and discuss the principle of generating broad-band vortex EM waves carrying multiple OAM mode based on the proposed antenna structure.Meanwhile,the influences of various parameters(arm number,growth rate,arm width,inner and outer radius,etc.)on the antenna bandwidth and the number of OAM modes are also studied.2.In order to generate broadband vortex EM waves carrying multiple OAM modes in air,the eflected currents travelling along ASA theory is proposed.An eight-arm Archimedean spiral antenna structure is designed accordingly,and only by controlling the inner and outer radius and changing the feeding networks of the antenna,it can generate vortex EM waves carrying three pairs of OAM modes(opposite polarizations and OAM modes)in the broadband of 1.9~3GHz.Finally,the effectiveness of the proposed antenna structure is also verified by the simulations,sample processing and experimental tests.3.A dielectric-loaded water-immersed horn array antenna is proposed to generate underwater vortex EM waves.Firstly,a dielectric-laoded single antenna is proposed.Under the premise of impedance matching,the ceramic dielectric of the suitable relative dielectric constant is loaded into the waveguide of the rectangular antenna to achieve better sealing,which can also greatly reduce the difficulty of assembly and experiments.Then,the simulation model of the eight-element antenna array is conducted and the generation of underwater vortex EM waves is verified by two simulation sofawares.4.For generating underwater broadband vortex EM waves carrying multiple OAM modes,a water-immersed impedance matching coaxial structure is proposed firstly.Using water as the filling medium of the coaxial matching structure,it can not only generate underwater EM waves in a wideband of 2~4GHz accordingly,but also reduce the difficulty of processing and assembly,which lays a foundation for the generation of underwater vortex EM waves.Then,based on the wideband single antenna,an eightelement broadband array antenna is simulated,fabricated and tested,and the simulated and experimental results show that the array antenna can generate underwater vortex EM waves of high quality in the same wideband of 2.1~4GHz.Meanwhile,the generated vortex EM waves can radiate far enough in water,which meets the requirements of the practical applications.Finally,for generating and detecting the vortex EM waves carrying multiplxed OAM modes,two generation methods based on the perfect composite phase and the concentric double-loop array,as well as a detection method based on the passive archimedean gap antenna are proposed,which have also been verified by simulations.5.Using the uniform circular array,the underwater EM vortex imaging model is established.The range and azimuthal resolutions of the EM vortex imaging on the underwater target are derived.The image reconstruction algorithms of Fourier transform and autoregressive model(AR)spectrum estimation are used to reconstruct the target,which also has been verified by simulations.And we can see that the AR spectrum estimation reconstruction algorithms have higher imaging resolution,but the scattering intensity of the target in the image generated by the Fourier transform reconstruction algorithm is closer to the real value.Our work has realized the generation of the broadband vortex EM waves carrying multiple OAMmodes in air and in water,which lays a solid foundation for the applications of vortex EM waves.As for the underwater target,the relative vortex EM imaging model has been established and verified by the simulations,which provides a meaningful reference for the expansion of the vortex EM waves' applications and the development of imaging technology.