The Finite-Difference Time-Domain method FDTD) is used to accurately characterize complex planar printed antennas with various feed structures such as coaxial probe feed structures. A new coaxial probe model is developed by using a three-dimensional FDTD technique. This model is shown to be an efficient and accurate tool for modeling coaxial-line fed structures. Use of new special modeling techniques in FDTD, such as thin-wire modeling and resistive voltage source modeling with application of nonuniform grids in this paper causes an extra compact model for probe feed microstrip antennas. Also, a novel use of implicit coupler model for dual feed components is presented that occupies no grid in analyzing space
