Fast and accurate methods to compute the mutual coupling between elements and with a finite ground plane are presented in this paper. The initial formulation is based on the Method of Moments (MoM). The HARP software presented here accelerates the MoM solution by using a combination of the Macro Basis Function (MBF) approach with an interpolatory technique. After that, those MBFs, which correspond to an infinite ground plane solution, are used to describe the interactions of the array with a finite ground plane lying on a semi-infinite soil. The methods are validated here for the SKA Log Periodic antenna (SKALA), under study for the Square Kilometer Array (SKA). The patterns are compared here with results obtained with the commercial software FEKO.