Research On Antenna Array Beamforming And Vortex Electromagnetic Wave

Beamforming technology of array antenna has been widely utilized in radar,communication,navigation,remote sensing,telemetering and other fields.Antennas with low side-lobe characteristics can improve the signal-to-noise ratio of the system,reduce clutter signal interference outside the main beam,and also improve the electromagnetic compatibility of the system and prevent detection by enemy forces.In order to meet the demand of wireless communication for spectrum resources,vortex electromagnetic wave,which would be one of new frequency reuse technologies to improve channel capacity,has attracted much attention.Combined with scientific research projects,this thesis takes the antenna array beamforming and orbital angular momentum(OAM)arrays as research goals.It mainly discusses the low side-lobe technology of array antenna considering the element coupling and the method of generating multiple OAM modes based on the special phase beamforming of circular array.The major works of this thesis can be divided into the following parts:1.The realization of low side-lobe slotted waveguide antenna is analyzed.1)The frequency band characteristics of the slot conductance are improved by changing the slots width and choosing the appropriate conductance distribution;2)By extracting the amplitude distributions of the slotted array,the slot conductance is modified by considering the coupling,so that the actual amplitude distribution of the antenna is constantly approaching the desired Taylor distribution;3)In order to improve the performance of the antenna in the entire frequency band,the side-lobe characteristics of the slotted antenna array at the side frequency are improved by re-optimizing the slot conductance distribution.4)Based on the research of the above three aspects,two waveguide slotted antenna arraies are designed: a broadband low side-lobe slotted antenna array and an ultra-low side-lobe slotted antenna array.2.The pattern bandwidth broadening method of the low sidelobe monopulse antenna is studied.1)Combined with the method of extracting the amplitude distribution of the slotted array,the amplitude distribution of the antenna in the azimuth plane is improved,and the low side-lobes beamforming of the antenna in the azimuth plane is achieved.2)By broadening the bandwidth of the feeding waveguide,the amplitude distribution of the pitch plane of the antenna at the side frequency is effectively improved,so that the radiation patterns bandwidth of the antenna's pitch plane can be improved.The factors that affect the working bandwidth of the feeding waveguide are analyzed.A new method to improve the resistance distribution of the feeding waveguide is proposed,so that the output amplitude distribution of the feeding waveguide is improved.3)Moreover,based on the analysis of the advantages and disadvantages of various magic T and 3d B couplers,a high-performance sum and difference network in the operating frequency band is designed.By cascading the designed radiating waveguide,feeding waveguide and network,a low side-lobe monopulse antenna with a certain pattern bandwidth is obtained.3.The low side-lobe beamforming method of broadband array antenna is discussed.1)Combined with hybrid particle swarm optimization algorithm,the array antenna beamforming method of active element pattern(AEP)is studied.With the proposed method,the problem that the narrow distance and strong coupling in the low frequency lead to a large difference between the actual and the theoretical results is solved.Thus,broadband lowsidelobe beamforming of array antennas can be realized.2)Based on the above method,a broadband low side-lobe Vivaldi antenna array operating in the ultra-short wave frequency band is designed.In order to suppress the generation of grating lobes,a new miniaturized Vivaldi antenna loaded with a folding arm is proposed.The antenna array composed of the proposed Vivaldi element achieves low sidelobe characteristics in scanning(±30°)states of 1.92 frequency doubling bandwidths;3)A broadband low-sidelobe log-periodic antenna array in the short-wave frequency band is designed based on the method of AEP combined optimization algorithm.The array element is miniaturized by folding the dipoles,and the beam coverage of the patterns on the pitch plane is achieved by inclining the antenna.Finally,the antenna array achieves low sidelobe characteristics in the scanning(±35°)states of 1.86 frequency doubling bandwidths4.The method of generating multiple OAM modes based on special beamforming of circular array is studied.1)Combined with theoretical analysis and example calculations to verify the feasibility of generating OAM in a circular array;2)A novel high-gain microstrip antenna is designed as the element of a circular array.By utilizing a parasitic patch loaded with two slots,the beamwidth of its E-plane pattern is reduced,so that the gain of the antenna is increased effectively;3)A Rotman lens that can meet the phase requirements of multiple OAM modes is designed.The two-dimensional aperture field equivalent theory is used to improve the output amplitude distribution of Rotman lens.So that the performance of the OAM radiation patterns is improved;4)To generate nine different OAM modes,the multiple-input and multiple-output Rotman lens is adopted to replace the complex network to feed the circular array.