In this paper a shielding effectiveness of protective metal enclosure with apertures and receiving antenna placed inside is numerically considered. The purpose of antenna, here considered as a dipole, is to detect the electromagnetic (EM) field level within the enclosure and to transfer this information via a coaxial cable to network analyzer. This follows the experimental procedure used to measure the shielding effectiveness of enclosure. Numerical model, based on the Transmission-Line Matrix (TLM) method and enhanced with so-called wire node, is used to simulate this experimental setup in order to investigate how much the antenna/cable presence underestimates the level of shielding effectiveness due to their two-way coupling with EM field inside enclosure. The numerical model is first verified with experimental results available in literature and then used to estimate the influence of radius and length of dipole-receiving antenna and the impact of cable presence on the distribution of EM field inside the enclosure and resonant frequencies shift
