Research On Radiation And Scattering Properties Of Radome,Antenna Arrays And Their Integrated System

The antenna system is an extremely critical part in wireless signal transmission,and antennas usually need to be protected by a radome to avoid the effect of the environment in engineering applications.The bottom of the radome usually has a metal plate that shields the coupling between the carrier and the array,thereby forming a closed antenna cabin.However,the electromagnetic amplitude and phase distortion caused by the radome and the complex propagation environment caused by the closed antenna cabin will affect the electromagnetic performance of the antenna in the cabin.Therefore,the research on the radiation and scattering characteristics of the antenna array and the antenna cabin,has important scientific significance and engineering value in the fields of communication,remote sensing,national defense and security.How to simulate the electromagnetic characteristics of antenna elements and arrays accurately,design lowcost and high-performance antenna arrays efficiently,evaluate the electromagnetic characteristics of antenna cabin systems reasonably,and improve the deterioration of antenna radiation performance caused by radome and the closed cabin effectively,are still problems that need to be solved urgently.In order to solve the above challenges,this paper conducts the research from the perspective of both radiation and receiving model to discuss and solve the problems of the analysis,optimization and design of antenna arrays and radome system.Firstly,the numerical analysis methods used in this work,including the basic principles of the integral equation method,the numerical implementation of the method of moment,fast solution techniques,and excitation models are introduced.Besides,the reciprocity principle of the electromagnetic structure in the linear system is also introduced as the basic theoretical support of this research.Efficient and accurate numerical models are the basis for analyzing the electromagnetic characteristics of antennas and antenna cabin systems.To solve the problems of resonance frequency shift,poor convergence,and large number of unknowns that occur when the traditional volume surface integral equation(VSIE)is used to analyze the microstrip antenna radiation characteristics,a new numerical simulation method suitable for rapid analysis of microstrip structures is proposed in this paper.The traditional model is innovatively improved from three aspects: selection of basis functions,processing of boundary conditions and reduction of unknowns.In order to improve the accuracy of the solution and eliminate the frequency offset problem of the traditional model,the quasi-static relationship of parallel plate capacitor is introduced in this model to describe the strong coupling relationship between the radiation patch,the ground plane and the dielectric substrate,establishing the field continuity boundary condition at the interface between the metal and dielectric.In this method,higher order hierarchical Legendre basis functions is used to replace the traditional RWG basis function to expand the surface current,which can better describe the edge current on the radiating patch when the antenna resonates,thereby the unknowns can be reduced and the convergence can be improved significantly.In addition,the electric displacement vector in the dielectric is directly expressed by the current on the metal surface,as a result,the unknowns only exists on the metal surface and the total number of unknown can be further greatly reduced.Compared with the traditional VSIE method,this method can significantly reduce the amount of unknowns while improving the solution accuracy and convergence speed,when analyzing the radiation characteristics of the microstrip antenna and its array.Then,based on the Poynting energy flow characteristics of antenna receiving model,a new efficient design scheme to improve the gain of antenna arrays is proposed in this paper.This scheme uses the Poynting streamline method to analyze the influence of the antenna on the surrounding energy distribution from the perspective of antenna receiving,visualize the relevant physical characteristics,and increase the understanding dimension of the antenna design.By studying the disturbance characteristics of the antenna under different matching conditions,the characteristic of the short-circuit dipole that does not absorb energy but can guide the energy flow direction is used to rationally design its placement position,and guide the originally scattered energy to the desired direction.Therefore,the energy absorption capacity of the adjacent antenna element is enhanced,the array aperture utilization efficiency and the array gain is improved.Compared with the traditional design method from the perspective of radiation,the proposed scheme provides a new tool for use in initializing,parameterizing,and guiding the optimization of array antennas.In addition,to improve the antenna radiation performance deteriorated by the strong coupling between the radome and the array element and the multipath transmission effect of the closed cabin,an evaluation and optimization strategy based on the ideal point source radiation model is proposed for antenna cabin system.This strategy uses a point source as the test source to realize the evaluation and optimal design of the antenna cabin system,by analyzing the amplitude and phase change information of the radiation field of point source before and after the add of radome based on the integral equation method.To provide more optimization freedom,this paper selects the excitation amplitude and phase of the array inside the cabin as the optimization domain,replacing the optimization of the traditional radome wall structure.Then,the phase change information extracted by the above strategy is used to set the compensation phase of each element to offset the influence of the cabin on the phase of the radiation field,thereby eliminating pointing errors.Based on the proposed evaluation method,the excitation amplitude of the array in the cabin is further adjusted by optimization method to suppress the high sidelobe level effectively.In addition,an amplitude grouping technique is further been used to simplify the complexity of feed network design in engineering applications and enhance the feasibility of the proposed optimization scheme.By using point source model to evaluate the antenna cabin system,on the one hand,it has considered the multipath transmission effect of the radiation field of each array element in the antenna cabin.On the other hand,it avoids the multi-scale problems caused by the analysis of the fine structure of the antenna,and improves the system prediction efficiency during the optimization iteration.This optimization strategy can increase the pointing accuracy of the antenna cabin system significantly and suppress the high sidelobe levels effectively without changing the radome structure.Although the above optimization strategy can effectively optimize the electromagnetic characteristics of the antenna cabin system,when the number of array elements in the cabin increases,the computational complexity will also increase.Finally,in order to solve this problem,this paper proposes an optimization strategy for the antenna cabin system based on the receiving model.Based on the principle of reciprocity,this strategy can realize the antenna cabin system evaluation,diagnosis and optimization,by analyzing the electric field information at the array grids inside the cabin when plane waves are incident from different angles.The electric field phase information at the array grids when the plane wave is incident from main lobe is used to set the compensation phase of each array element,effectively eliminating the pointing error introduced by the antenna cabin.By comparing and analyzing the response of the electric field at each array grid to the plane wave incident from the main lobe angle and the side lobe angles respectively,the sensitive elements with higher influence on the high side lobe level and less influence on the main lobe gain can be located to determine the optimization domain.Then,the excitation amplitude of the elements in the optimization domain is adjusted by optimization algorithm to achieve effective suppression of high side lobes.In addition,in order to solve the problem of non-uniform excitation caused by this optimization strategy,an antenna rotation scheme is further introduced in this paper.The high side lobe level of the cabin system can be effectively suppressed,only by rotating the array elements in the optimization domain by appropriate angles without the modification of radome structure or designing a complex feed network.The computational complexity of this optimization strategy is only related to the number of optimization angles,but not to the number of array elements in the cabin,and only the adjustment of the excitation weight or placement angle of the sensitive elements of the antenna array is required,therefore,compared with the radiation model,this optimization strategy has higher optimization efficiency and greater application potential when optimizing large array antenna cabin systems.