| The orbital angular momentum(OAM)of vortex wave with spiral phase has infinite modes in theory and different modes are orthogonal to each other.The spectrum utilization rate and communication capacity can be greatly improved when using the mode number of OAM vortex wave used as the modulation parameters.Therefore,some people believe that OAM multiplexing technology is expected to be a transmission technology used in the next generation of mobile communication systems.The thesis starts from some research backgrounds of OAM vortex wave,systematically introducing backgrounds and current researches,followed by fundamental theory of OAM vortex wave and mechanism of OAM vortex waves generated by a circular array,which provide a solid theoretical foundation in order to carry out the following work.In this thesis,the generation methods of OAM vortex wave have been introduced and compared in detail,and the method of a circular array in microwave or radio frequency has been improved.The single-arm spiral antenna(SASA)which allow self-rotation around the axis to produce a relative change in phase of the radiated field in space.One degree of mechanical rotation produces a corresponding change in phase of one electrical degree.The feed network can be simplified as a uniform power divider whose amplitude and phase of eight output ports are all same to different OAM modes due to the rotation property of SASAs.A single-arm spiral antenna can be designed to generate the right-hand(RH)circular polarization electromagnetic wave and the operating bandwidth is during 1.73-9GHz.It is an effective way to generate OAM-carrying radio beams using a circular antenna array.In this thesis,the circular array consists of eight identical SASAs whose excitations have the same magnitude and phase,but the phase difference required for different OAM modes can be achieved by mechanically rotation of the SASA.The vortex waves with different OAM modes can be generated by the circular array antenna in a wide band from 3.4GHz to 4.7GHz.The prototype of the circular array is proposed,conducted,and fabricated to validate the theoretical analysis.The prototype of OAM-generating SASAs array was fabricated and measured,and results of the far-field and near-field sampling measurements have agreement with the simulation results,which verifies the effectiveness and correctness of the proposed reconfigurable OAM method.Furthermore,the purity,the detection method and receiving condition are studied in this thesis.Due to the periodicity of the phase,the OAM vortex wave generated by circular array antenna is not pure enough to communicate information,it is necessary to analyze the purify of modes of OAM vortex wave.Then,two detection methods of OAM vortex wave have been studied.What's more,the transceiver system of OAM vortex wave according to the corresponding reference has been analyzed and simulation results show the transmission coefficient of the same mode is much higher than the transmission coefficient between different modes,which prove that different modes of OAM vortex wave have good isolation characteristics,that is beneficial to communication transmission.The rotation angle of each SASA needs to be revolving around its own axis when the direction of the main beam generated by the circular array antenna is deflected based on the principle of planar microstrip reflectarray antenna.In addition,the OAM vortex waves with different modes of different frequency bands are generated by using the circular array antenna with two circles inside and outside.In this thesis,a mechanically reconfigurable circular array with SASAs is designed,fabricated,and experimentally demonstrated to generate broadband circularly polarized OAM vortex waves in radio frequency domain.The proposed method paves a reconfigurable way to generate multiple OAM vortex waves with spin angular momentum(SAM)in radio and microwave satellite communication applications. |
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