Prediction and Validation of Electric Fields in a Scale-Model Aircraft Fuselage Based on a Friis-PWB Hybrid Model Incorporating Incidence Angle Effects

This study proposed a hybrid approach that combined the Friis equation and power balance (PWB) theory to predict the internal electric field of a large metallic enclosure and experimentally validated the method using a 1:25-scale aluminum enclosure representing an aircraft. Its applicability at the full aircraft scale was further verified through simulations. For the window apertures, we summarized the continuity conditions for the average coupling cross section and critical frequency in the electrically small/large regimes and incorporated the dependence on the angle of incidence. The internal power and electric field were obtained from a power balance equation based on the quality factor and loss terms, and the incident power density from the Friis equation was summed over individual windows. In the experiments, a horn antenna was swept from 1 to 10 GHz in 500 MHz steps, fields at nine interior points were probed and averaged, and cable losses were corrected using a VNA. The measured values as a function of incidence angle typically agreed with the predictions within ±5 dB. Full-scale aircraft simulations agreed with the predicted values. Because the proposed method accounts for angular effects but remains simple to compute, it is useful for rapid electromagnetic safety assessments of large structures. Future work will incorporate horizontal polarization and a fully three-dimensional incidence model to further improve accuracy.