Finite Difference Time Domain Method In The Application Of Multi-Antennas Systems On The Vehicle

In recent years, the finite difference time domain method(FDTD) is widely applied in numerical calculation of antennas. Especially, the electromagnetic compatibility(EMC) analysis of multi-antennas which are all located on a complex vehicular platform is a hot issue in the numerical calculation of electromagnetic fields. Due to the simple calculation form and its strong graphical visualization, FDTD is a powerful auxiliary tool in the design of antenna layout on the vehicles.Firstly, Maxwell’s curl equations are discretized in terms of traditional Yee grid.The conductivity and permeability of different directions within PML layer are designed detailedly and the calculation formulas of corresponding electric and magnetic field component in the PML layer are derived. In order to eliminate the discontinuity in electromagnetic parameters between the PML medium and the free space, Pade approximation is introduced to unify the iterative formula in the whole computational domain.Secondly, the electromagnetic parameters which include S parameters, radiation pattern of monopole antenna and patch antenna are obtained by FDTD method. The change of the antenna’s input impedance is also considered when it moves on a rule carrier. The far field information of an antenna is achieved by using near-to-far field transformation on the basis of equivalence principle. Some examples are employed to validate the effectiveness of the two feeding methods based on these two simplified feeding model. When the non-uniform grid algorithm based on inter-coordinate transformation method is introduced to generate a finer mesh in the near-field area where the electromagnetic field changes intensely, the number of computational grid can be effectively saved. In order to display electromagnetic field in the near field dynamically, the OpenGL technology is used. At the same, plane wave is introduced exactly from vertical or oblique direction through the connective boundary condition.Finally, the coupling characteristics and layout of multi-antennas on the same vehicular platform are studied on in this thesis. The complex vehicle model is dissected into meshes by the open software GiD. A new method is proposed to transform the Gi D meshes into the relative coordinate of Yee grid. In order to improve the computational efficiency, OpenMP based on shared memory is used to obtain a parallel computing.Then, the following work is completed based on the those meshes:1. The corresponding electromagnetic parameters of a single antenna which is in different positions on the vehicular platform is calculated and analyzed. The best installation location for a single antenna is obtained through comparing the influence on those parameters.2. The influence on the coupling of double antennas caused by their distance is also analyzed. The interpolation S21 function is obtained by finite sampling in the feasible region and the results shows that it can effectively predict the best installation location for them. This work has a certain innovation.3. The mutual coupling characteristic among antennas with different working frequency in multi-antenna system and the effect on the radiation pattern of source antenna caused by receiving antenna is also discussed. The mutual coupling paths between the source antenna and the receiving one are depicted through electric field distribution on the vehicular platform. Those work is valuable to multi-antenna layout on the vehicles.