Research On Analysis And Control Methods Of Radiation And Scattering Of Antenna Arrays

Since the phased array system can conveniently control the shape and direction ofthe radiation beam according to the requirements, it was used on many militaryplatforms. Along with the rapid development of stealth technology, the radar crosssection (RCS) of a target has been availably controlled. For the low observable platform,the scattering from the array antenna mounted on it often becomes a major contributionto the RCS, which restricts the stealth effect of the whole system. Therefore, radiationand scattering tradeoff design of antenna array is of great significance to the design of astealth system. The analysis and calculation of the radiation and scattering from arraysare the precondition for this design. Being associated with the research project, thisdissertation is mainly concerned with the RCS analysis, calculation and control methodsfor the antenna array, the author’s major contributions are outlined as follows:1. The basic theory of genetic algorithm (GA) and particle swarm optimization(PSO) and their applications for pattern synthesis of arrays are investigated. Meanwhile,the low sidelobe linear and concentric ring antenna arrays are analyzed. Then severalimproved strategies based on the modification of the optimal model are proposed, whichcan greatly reduce the computation cost and the analysis time of either optimizationalgorithm applied to solve this problem. Numerical results show that the proposedoptimization algorithms can achieve better results compared with available methods.2. An approximate method is presented to accurately calculate the radiation patternof large finite arrays, depending on the knowledge of the active element pattern (AEP).The active element patterns of all the elements of the large array are deduced from asmall array by ignoring the coupling beyond the small array size. Consequently, theapproximate method converts the large array calculation problem into a small arrayproblem and greatly reduces the computational cost and the analysis time. In addition,an accurate and efficient synthesis method is proposed by using the approximate methodto evaluate the fitness function of the optimization algorithm, such as GA and PSO.3. The concept of the above AEP method that is used to solve the array radiationproblem is extended when scattered fields of large finite arrays are calculated. Themethod transforms the large array calculation problem into a small array problem, andthereby greatly reduces the computational cost and the analysis time. Meanwhile, theeffects of the mutual coupling between elements and the edge diffraction are rigorouslytaken into account. Then, the formulas for calculating the structure mode and antennamode scattered fields are derived, which is of great guiding significance to the RCSreduction of antenna arrays.4. Based on above formulas and theoretical analysis, the concept of array radiation pattern synthesis is extended to simultaneously control the radiation and scatteringcharacteristics of arrays. In the proposed method, the optimization methods areemployed and the element positions and excitation phases are selected as the optimalvariables. The proposed synthesis method is applied to tradeoff design the radiation andscattering characteristics of a microstrip patch antenna array and a horn antenna array.By optimization, the radiation performances of the arrays are both improved and theRCS of the arrays are both availably reduced.5. The closed-form expression is derived for the radiation and scattering fromdipole arrays based on the equivalent circuit method. Since the radiation and scatteredfields expressed in this way are both a function of the element positions, a method isproposed for simultaneously synthesizing prescribed radiation and scattering pattern byoptimizing the position of each dipole in an array. Several arrays are designed with theproposed method to assess the validity and efficiency of the proposed method.6. The formula for calculating the radiation field of large conformal arrays isderived based on the AEP technology and the above subarray method. The derivedexpression transforms the large conformal array calculation problem into a smallconformal array problem, and thereby greatly reduces the computational cost and theanalysis time. Meanwhile, the effects of the mutual coupling between elements and theinfluence of the platform are rigorously taken into account. Several microstip antennaarrays mounted on the surface of a cylinder and a cone are analyzed with the proposedmethod to verify the validity and efficiency of the derived expression.