In this paper, the electromagnetic characteristic of multi-antennas on a vehicular platform is analyzed using the finite-difference time-domain (FDTD) method based on the UPML boundary. The FDTD method is a kind of transient time domain method, which derived directly from the Maxwell's equations in the time domain. The FDTD method can simulate the propagation processing of electromagnetic wave very clearly. If the excitation is a pulse source, the response in frequency domain can be obtained over a wide ban...