A number of interesting applications of the equivalent-current/source method (EQC) have recently been presented for antenna design and diagnostics. The Dual-Equation formulation has been proven to be superior in terms of accurately reconstructing sources on, or very near, the AUT structure, and is the only formulation directly applicable for diagnostics [1]. The maximum antenna size that can be handled by this method is limited by memory and running time constraints, due to the construction and solution of the linear system describing the problem. This paper reports the enhancement of the Dual-Equation formulation by the integration of the Fast Multipole Method, which allows dealing efficiently with large antennas.