Abstract: A physical model is presented for linear coupling of microwave pulses into apertures in cavities. The numerical simulation method of FDTD and absorbing boundary conditions are dis cussed. We calculate coupling processes of microwave pulses into apertures with various size and different positions, and an alyse the dependence of coupling on aperture size and polarization direction of the incident field.

Key words: microwave pulse, linear coupling, finite-difference time-domain (FDTD)