Electromagnetic pulses (EMPs) can couple into electronic equipment cavities through apertures, causing severe interference and potential damage. Understanding the coupling characteristics and resonance mechanisms is critical for improving electromagnetic protection design.

This study aims to investigate the coupling effects of EMPs on rectangular cavities with apertures, focusing on field distribution, resonance behavior, and the impact of incidence conditions.

A numerical model of a perfectly conducting rectangular cavity was established using the Finite-Difference Time-Domain (FDTD) method. The study analyzed electromagnetic field distributions inside the cavity under varying incidence angles and continuous pulse excitations. A time-frequency joint analysis method was applied to reveal the resonance mechanisms of aperture coupling.

The results show that aperture coupling produces significant electric field enhancement at specific frequencies, with peak amplitudes several times larger than those of the incident field. Normal incidence yields the strongest resonant effects, while oblique incidence leads to different responses in electric field components due to boundary constraints. Continuous pulse excitation results in electric field energy accumulation, though it is limited by standing-wave effects. The resonant frequencies were found to be highly dependent on cavity dimensions, confirming the frequency-selective characteristics of aperture coupling.

This research establishes the theoretical basis for understanding EMP aperture coupling and provides technical references for designing protection measures in high-intensity electromagnetic environments.