Generation And Application Of PSOAM Beam Based On Microstrip Array

Orbital angular momentum(OAM)is widely used in wireless communication,radar imaging,and electromagnetic sensing because of its unique orthogonality and vorticity.However,the inten-sity dark zone in the center,beam divergence and the inconsistent divergence angles of different modes make it difficult to achieve effective mode multiplexing and long-distance communication.Our group proposed a plane spiral orbital angular momentum(PSOAM)beam.This beam is a special fom of the OAM beam,which adjusts the divergence angle of the beam to the direction where the elevation angle equals 90°.In this way,the divergence angles of all the PSOAM beams are consistent,the problems mentioned above are overcome to some extent.Moreover,the struc-tured electromagnetic wave with controllable amplitude and phase can be constructed by superpos-ing different PSOAM beams,which provides a new idea for the application of OAM.This paper mainly studies the generation of multi-mode PSOAM beams and their applications in constructing the structured electromagnetic waves.In this paper,a circular microstrip array antenna which can be used to simultaneously generate PSOAM beams with multiple modes is demonstrated.The number of microstrip elements is eight,and the PSOAM modes that can be generated are 0,± 1,±2 and ±3.The center frequency is in the X-band.The design of the microstrip antenna element and the whole circular antenna array structure are realized based on theoretical calculation and software simulation.In order to simultaneously generate multiple mode PSOAM beams,a 8 x 8 Butler network is adopted as the feed structure of the microstrip array antenna.In this paper,the three conponents of the Buter network,such as 3dB directional couplers,OdB cross couplers and phase shifters are firstly designed and then they are combined to constitute the whole feed network.The performance of the Butler network is simulated,and the simulation reaults have verified its validity for the generation of multi-modes PSOAM beams.At last,the construction of the structured electromagnetic wave based on the superposition of the generated PSOAM waves are studied.The field distribution of azimuth angles of different PSOAM beams can be regarded as a kind of orthogonal basis for the azimuthal domain of elec-tromagnetic waves.Therefore,theoretically any azimuthal distribution of electromagnetic beams can be achieved by the superposition of PSOAM beams.Various beamforming are achieved by superposition of PSOAM beams of different mode combinations generated by the microstrip array antenna.In addition,by adjusting the initial phase of the superposed PSOAM beam,the direction of the main lobe of the synthetic beam changes accordingly,then the distortion-free beamscanning in two-dimensional plane is achieved.The simulation results agree well with the theoretical analysis,which prove the advantages of the structured electromagnetic wave based on the PSOAM.