Abstract: Full wave method FDTD was used to design and analyse wideband planar antennas, in order to acquire the impedance of three kinds of slotlines, Mur's ABCs of the second order and partial absorbing load was taken into account to reduce the reflection on the boundary conditions. Comparison with the MoM and Serenade software as well as experiments verified the accuracy and readiness of this method. Finally, the pattern of Vivaldi antenna (based on the double sided slotline) was obtained.