Analysis And Research On Gaussian Beam Based High Frequency Method

With the development of science and technology, analysis of electrically large object is needed in computational electromagnetics. Compare with the full wave method, physical optics(PO) which has been widely used in analysis of electrically large problems has advantages such as low computer resource usage, fast computational speed, etc. However, direct numerical integral of the PO current is also time-consuming. This integral can be simplified when Gauss beam(GB) is adopted. In this thesis, the application of frequency domain GB(FDGB) in calculation the integral of frequency domain PO(FDPO) currents over quadric surface and Non-uniform Rational B-Spline(NURBS) surface, the application of time domain GB(TDGB) in calculation the integral of time domain PO(TDPO) currents over Impulse Radiating Antenna(IRA) and model composed of triangles, the application of FDGB in analyzing radiation and scaterring probolems of infinite periodic array are discussed. This research mainly focuses on:Firstly, basic parameters of FDGB are introduced. The theory for calculation the integral of FDPO currents over quadric surface when it is illuminated by FDGB is presented. This integral is analytical and independt of frequency. The computational efficiency of FDPO currents’ integral is improved greatly. In local coordinate system, the quadric surface approximation of reflector antenna is shown. By matching its far-field pattern in FD, the field radiated by the horn is expanded in terms of FDGBs. The magnetic field on the axis of FDGB is found by two order interpolation. The total radiation field of quadric surface when it is illuminated by the horn antenna is found by superposition of the PO field when quadric surface is illuminated by each FDGB. Using this method, radiation characteristics of electrically large reflector antenna with symmetrical and asymmetrical structure are simulated. Phased array feed reflector antenna which has limited scanning ability is also analysed. The contribution of FD diffraction field is found by method of FD equivalent edge currents(FDEEC).Secondly, the application of FDGB in calculation the integral of FDPO currents over NURBS surface is presented. The basic theory of NURBS surface and its advantages in modeling are introduced. The intergral of FDPO currents over NURBS surface when it is illuminated by FDGB is calculated with Delaminating Quadrature Method(DQM) which is stable, accurate and independent of frequency. The computational efficiency of FDPO currents’ integral is improved greatly. In the form of NURBS surface, the scattered field of electrically large perfectly conducting plane, cylindrical patch and spherical patch is calculated. High order NURBS surface is also analyzed. The effect of FDGB waist to those above examlpes is discussed.Thirdly, basic parameters of TDGB are introduced. The method to calculate the step and impulse response of IRA which is illuminated by TDGB is presented. With the appropriate coordinate transformation, the two-dimensional integral of IRA’s step and impulse response can be reduced to one-dimensional integral, which is independent of IRA’s size. The above method consumes only a little computer resources to simulate the model while CST requires enormous resources. Adaptive time interpolation is adopted when the impulse response changes rapidly. The transient response of IRA which is illuminated by a single TDGB is obtained by convoluting the impulse response and the excitation signal. The TD field radiated by a horn antenna is expanded in terms of TDGBs by matching its far-field patterns in FD. By superposition theorem, the total transient response of IRA illuminated by the horn antenna is obtained. The contribution of TD diffraction field is calculated with the method of TD equivalent edge currents(TDEEC).Fourthly, the application of TDGB in calculation the integral of TDPO currents over structure modeling with triangles is presented. Triangle meshing which is widely used in computational electromagnetics has advantages such as simplicity, ability to describe complex models, etc. Illuminated by TDGB, the two-dimensional integral of TDPO currents over structure modeling with triangles can be simplified to one-dimensional integral. The computational efficiency of TDPO currents’ integral is improved greatly. The shaded area of PO is determined by z-buffer algorithm which is based on GB propagation characteristics. Using the above method, transient responses of electrically large perfectly conducting plane, Fresnel zone plate reflector antenna(FZP), missile and aircraft are simulated.Finally, the application of FDGB in analyzing radiation and scaterring probolems of infinite periodic array is introduced. In order to exhibit a Gaussian taper excitation, the focus point of one- and two-dimensional infinite periodic array is placed in complex space. By adopting Poission sum formula, radiation fields of these arrays are transformed to terms of Floquet modes. Summation of Floquet modes which exhibit characteristics like a FDGB has fast convergence speed. The scattered field of one-dimensional infinite periodic array which is illuminated by a complex source beam(CSB) is also analysed. By adopting Poission transformation, the slowly convergent superposition of individual radiation field from infinite array is transformed to terms of Floquet mode which has characteristics like a FDGB.