Electromechanical Coupling Oriented Analysis And Synthesis Of Random And Systematic Errors In Microwave Antennas

Recently, as the microwave antennas move towards large aperture, high frequency, high gain and high pointing accuracy, the electromechanical coupling problems have become more and more prominent between mechanical structures and electromagnetic parts. Systematic and quantitative studies have been performed on the effects of random and systematic errors on the electrical performance of reflector antennas and array antennas based on the electromechanical coupling theories.The average power pattern model of reflector antennas is established considering the effects of random errors and systematic errors. The average expression of the difference of phase errors between any two points in the aperture plane is derived induced by the machining errors of single panel and misaligned errors of panel frames attached to some panels, on the base of the assumption that the random errors have a Gaussian distribution with some correlation interval on the reflector surface. Phase errors caused by systematic deformation are treated in a way of feed defocus. The closed-form expressions of correlation function for tapered illumination are derived from incorporating the axial defocus of feed caused by systematic deformation, and then the average power pattern on the overall effects of random and systematic errors is obtained. Finally, detailed parametric simulations are performed based on the proposed model on the effects of random errors and systematic errors on the gain, sidelobe levels etc., with an example of 6.2-m reflector antenna. Some valuable data results and curves are also shown.A novel and practical approach to determine the effects of machining errors on the electrical performance of large reflector antennas is presented based on paneled forms. The panels are divided into three parts:panels in different rings, panels in one ring but different parts, and panels in the same ring and parts, according to the fact that the panels in actual reflector antennas machines individually. As to the power of different panels, the respective average fields are calculated firstly, and then by multiplying the two values to get the far-field power. As to the power of the same panels, the correlation functions of machining errors in different positions are defined firstly, and then the quadruple numerical integration of average power pattern is performed in the area of a single panel. Finally, the average power pattern of whole antenna is obtained based on the sum of the three mentioned panel powers. Detailed parametric simulations are performed to demonstrate the effects of different machining precisions and paneled forms.A novel errors diagnosis scheme is developed based on the B-spline and Moran’s I. The parameter direction and parameterization method are defined based on the fact that the reflector surface is semi-closed, and then the least squares fitting of B-spline curves in the u and v direction is employed to establish the regression model of the deterministic surface. Subsequently, a spatial statistical analysis is performed to determine whether the spatial independent distribution of the residuals is attained for a given confidence level in order to extract the random errors and systematic errors. The presented methodology has been applied to the surface analysis of a 3.7 m reflector antenna.A mathematical model is created to determine the effects of the structural errors on the polarization characteristics of the array antennas. A general process of rotation transformation from global-coordinate system to arbitrary local-coordinate system of elements is exhibited by transforming the coordinates three times orderly. It is shown that corresponding polarization pattern of elements can then be derived, based on which the global polarization pattern of the array. Parametric studies are performed in detail to evaluate the effect of assembly precision and flatness on parameters such as gain and polarized characters by using a 9x5 planar array, and some useful engineering results are presented.The effects of the structural deformations on the electrical performance of Log-Periodic Dipole Antennas (LPDA) are investigated based on the electromechanical coupling theories. The elementary and electromechanical coupling model of LPDA is established based on the computing method of electrical performance and structural deformation analysis, in which the effects of excitation currents, position offset and direction deflecting of dipoles are considered. A software platform integrating structure and electromagnetics to a whole is developed to perform the electromechanical integration analysis of LPDA, and then applied to a 4 fan-shaped LPDA array.