Currently, interest in the prospects for practical implementation of methods that allow retrieving the true radiation pattern when irradiating the navigation antenna under test from an insufficiently large distance is noticeably growing. The use of directed radiation in this case, on the one hand, reduces the level of reflections from the walls of the chamber, but on the other hand, increases the heterogeneity of the irradiating field. The paper aims to elucidate the influence of the directed properties of the auxiliary antenna, which forms the irradiating field, on the measurement process and the accuracy of the radiation pattern retrieval, under the condition that both of them are by the methodology of a converging cluster of plane waves. Simulating measurement and data processing were carried out when the size of the auxiliary antenna varied. The simulation results confirm that the reconstruction accuracy is practically independent of the nature of the irradiating field.