Fast and efficient FDTD analysis using non-uniform mesh for small antenna

The FDTD method is readily available for the analysis of the three-dimensional mixed-dielectric problem. However, the wavelength inside high dielectric constant material is shorter than in free space, the cell size must be determined by the shortest wavelength. The other problem of FDTD analysis is modeling the target antenna structure precisely, such as thin wires, or narrow slots that are very small compared to the main body of the other objects. If an uniform cell size is used throughout this problem, the cells in all the analysis region must be relatively small, which may greatly increase the total number of cells. To reduce the cell size and avoid an increase of the arrays in the computation, the FDTD method by using subcells in specific regions and a non-uniform mesh in the computational space has been proposed. However it has been also reported that the computation diverges if the ratio between two difference mesh sizes is larger than two. This paper presents the FDTD method by using different meshes with a large ratio of more than two. By interpolating the magnetic field component between the fine mesh and coarse mesh, the computation accuracy can be improved by a simple algorithm, and this algorithm is examined for a monopole mode patch antenna.