Research On Properties And Applications Of Radio Electromagnetic Wave Carrying Orbital Angular Momentum

The electromagnetic wave carrying orbital angular momentum(OAM)has both orthogonality and vorticity.The orthogonality that the OAM waves with different topological charges(TC)are orthogonal between each other provides a new physical dimension of freedom for the information multiplexing and modulation.The vorticity that the OAM waves with different TCs have various phase fronts increases the space phase diversity.Therefore,the new electromagnetic technologies based on OAM will bring new opportunities to the traditional electromagnetic applications and have great potentials.In this thesis,based on the current research status of the OAM wave,the problems need to be solved for the radio OAM wave are thoroughly analyzed.To solve such problems,the local properties of radio OAM wave,the new performance characterization of radio OAM antenna,and the key technologies of radio OAM wave in electromagnetic applications are mainly studied.Compared with the optical vortex,the radio OAM wave has a larger divergence angle.It is difficult to receive a full aperture radio OAM beam in practice.Thus,the traditional angular momentum(AM)theory is not applicable for the radio OAM wave's practical application.In the thesis,the local AM properties of radio OAM wave are theoretically analyzed from the point view of the practical application,which enriches and expands the OAM theory in the radio frequency domain.So far as we know,it is the first time that a new component of the local CAM is proposed,and analyzed by an orthogonal polarization mode decomposition method.Based on the analysis of the local CAM,the local AM decomposition of an arbitrary polarized OAM wave has been derived.Moreover,the TC local estimation method for an arbitrary OAM wave is also proposed.The study of the radio OAM wave's local AM properties provides an effective theoretical foundation for the local use of radio OAM wave in the future.The existing characterization parameters for the radio OAM antenna rarely consider the practical applications of radio OAM wave.To solve this problem,several new characterization parameters are proposed including the receiving pattern,the purity related bandwidth,and the mode phase linearity.Compared with the traditional antenna indexes which are only related to the amplitude of radiation wave,these newly defined characterization parameters fully consider the amplitude and phase distributions of radio OAM wave and its mode demodulation method in the real practice.They are used to characterize the performances of a fabricated wideband OAM helix antenna with L=3 at 10GHz,it is found that these new characterization parameters have an effective guidance for the OAM based application.To fully exploiting the azimuthal wave vector of OAM wave,the rotational Doppler effect of a radio OAM wave is studied in the thesis.Considering the serious divergence of radio OAM wave,an experimental system based on local receiving is constructed.The influence factors including the deflection of the receiver and the rotating plane are analyzed in detail.For the first time,the radio rotational Doppler frequency shifts are experimentally measured when the incident radio OAM waves' TCs are larger than 1,which can be used to get a higher accuracy for the azimuthal velocity measurement.To mitigate the influence of the deflection of the receiver and the rotating plane,a detection scheme to measure the two-dimensional vector velocity by using plane spiral orbital angular momentum(PSOAM)wave is also proposed.Finally,the new application systems of the PSOAM based structured electromagnetic wave are preliminarily explored in the area of radar imaging and wireless communication.When the directional structured electromagnetic wave superposed by a set of PSOAM waves are azimuthally scanned,the azimuthal imaging can be realized by using the additional information provided by the OAM wave.With the help of the commonly used multiple signal classification(MUSIC)algorithm,a higher azimuthal imaging resolution than that of the traditional OAM imaging system can be obtained by taking advantage of the high gain of the directional beam.A new multiple input and multiple output(MIMO)communication system based on the PSOAM based structured electromagnetic wave is also proposed.Owing to the orthogonality,vorticity and the high gain of the PSOAM based structured electromagnetic wave,a higher capacity gain is obtained compared with that of the traditional MIMO system.The obtained results show that the PSOAM based structured electromagnetic wave will provide new ideas for the application of radio OAM wave in the traditional electromagnetic field.