Fast And Accurate Analysis Of Electrically Large Body-of-Revolution Radome

With the rapid development of the military electronic technology, the modern warfare puts forward more and more requirements to the precision guidance of aircraft and missile. The airborne radome is necessary for providing physical protection to the antenna, but at the same time it affects the electromagnetic properties of the antenna to a certain extent. Therefore, the accurate electromagnetic analysis to the antenna-radome integration system is not only of theoretical significance, but also of national defense application value. Due to the electrically large size of the airborne radome, the accurate analysis to it is usually carried out through parallel computing or on a large workstation. Considering that most of the airborne radomes have the rotationally symmetric structure property, we can reduce the computational requirements by taking advantage of this property. Closely associated with the defense project, by utilizing the structure property of the radome and making a series of improvements, we realize the fast and accurate analysis of the electrically large antenna-radome integration system on the personal computer. Aiming at the key and difficult problems met in the analysis of the body of revolution radome, this dissertation makes in-depth research. The author's major contributions are as follows:1. The modeling method based on the surface integral equation is presented to model the antenna-radome integration system. For the two cases that the radome bottom closes and uncloses, two equivalent models are established based on the equivalence principle. Then from these two models, the principle and process are presented in detail that how the surface integral equations and the moment-method matrix are established. In order to retain the accuracy of the method of moments (MoM) and reduce the computational requirements, a modeling technique based on the hybrid method of moments-physical optics (MoM-PO) is also introduced.2. A method to fast calculate the mode decomposition coefficients of the incident field is presented. By sampling, the incident field that is periodically distributed along the azimuthal direction on the radome surface is then transferred from continuous-space signal to discrete-space signal. Correspondingly, the Fourier Transform is translated into the discrete Fourier Transform, which can be performed by the Fast Fourier Transform (FFT). All modes'decomposed coefficients of a field component on a certain segment can be obtained with one FFT computation. It avoids the too long computing time caused by the individual computing under every mode when the conventional integral method is used.3. A method is presented to efficiently select the minimum number of calculated modes. For the MoM based on the mode decomposition technique, which is adopted in the analysis of the rotationally symmetric object, the computation time is proportional to the number of modes that MoM processes. On the one hand, if the number is too small, the computing result will not reach convergence. On the other hand, if the number is too large, it will cause unnecessary computation. Based on the Parseval theorem and by introducing the energy spectrum graphs and the average energy coefficients, a method to fast and accurately determine the minimum calculated mode number is introduced. It will alleviate unnecessary computation burden and save a lot of time.4. Under the local curvilinear coordinate system of the radome surface, the computing of the impedance matrix elements is introduced. Starting from the established electromagnetic surface integral equations and through detailed derivations, the computing expressions of the impedance matrix elements are presented. In order to avoid the integration of the arc length, every triangular function along the generatrix is approximated as four subsection pulse functions. By adding a perturbation, the fussy singularity processes in the computing of the matrix elements are avoided when the test point and the source point are superposed.5. The characteristics of the impedance matrix are distilled, such as the symmetry of the matrix, the correspondence between the matrix elements of the positive modes and that of the relative negative modes, and the superposition of the basis functions. By utilizing these characteristics, a series of improvements are made to reduce the computation and memory requirements extremely.6. A method is presented for the fast calculation of the far-field pattern of the antenna covered by the body of revolution radome. Two far-field calculating methods that directly by the surface integration and by the reciprocity theorem are introduced respectively. In both methods, the integrals with respect to the azimuthal angle are carried out in closed forms so that it's easily to calculate the far-field pattern fast and exactly.7. When the scanning property of the antenna-radome integration system is analyzed, the sameness of the impedance matrix for various scanning angles can be utilized. Under every calculated mode, the equivalent current coefficients for all the scanning angles are calculated simultaneously to share the inverse of the impedance matrix, thus the processes of filling the impedance matrix and getting its inverse needn't to be carried out repeatedly for various scanning angles. As an example, the scanning property of a large array antenna in the presence of a radome is analyzed and some parameters are calculated, such as the attenuation of the main lobe and the boresight error.