Research And Application Of Theory Of Characteristic Modes In Periodic/Quasi-periodic Structure

The periodic/quasi-periodic structure is composed of arrays of identical/different elements,such as phased array antennas,metasurface,frequency selective surface,reflectarray,and so on.The periodic/quasi-periodic structure is wildly used in communication,aerospace and other fields,and involves many subjects including electromagnetism,microelectronics,computer and others.The importance of its research and the complexity of technology can be imagined.With the size of array increasing,the analysis of electromagnetic characteristics related to the array becomes more complex.How to develop a fast analysis method for this kind of structure has become a research hotspot in related fields.Based on the Theory of Characteristic Modes(TCM),a new method to analyze the electromagnetic characteristics of quasi-periodic structures is proposed.In this method,one element is selected as the reference element,and the geometric information of it is used to construct other elements'.The elements of array can be changed in any size or rotation angle.The eigencurrent of reference element is obtained by solving the generalized eigenvalue problem,and by using mode truncation method,choose the first few Characteristic Modes(CMs)with larger modal significantly to construct the entire domain basis function of array,and then use this group of entire domain basis functions to expand the induced current of array,finally solving matrix equation to analyze the electromagnetic characteristics of array.On this basis,the Mixed-Potential Integral Equation(MPIE)is combined with the Discrete Complex Image Method(DCIM)to investigate the electromagnetic characteristics of microstrip quasiperiodic structures.By reducing the unknown quantity,the method greatly reduces the computation time and the memory required,and realizes the fast analysis of quasi-periodic structures.In addition,a new method of radiation pattern synthesis for phased array antennas is proposed,which is based on Multi-Objective Evolutionary Algorithm based on Decomposition(MOEA/D).Firstly,the eigencurrent and eigenfield of the phased array antenna are obtained by using the fast analysis method of array's CMs.Then the radiated current and radiated field are reconstructed by using the orthogonal characteristic of the CMs.In addition,according to the specific requirements,three objective functions are given to set the orientation angle of the main beam,the range of the main beam and the radiation energy of the pattern.The reconstructed field and reconstructed current are substituted into the optimization and iteration,until the convergence is achieved.Finally,the phased array unit is fed according to the amplitude and phase of the optimized feed,and the result of radiation pattern synthesis is close to the expected target.