MELISSA is a GB-SAR system used for monitoring of the Tessina landslide in Italy. It uses 12 horn antennas for transmission and 12 vivaldi antennas for reception of the transmitted signal. The 12 horn antennas which have been placed in a linear geometry in MELISSA, when placed in a 2 × 6 planar geometry, yield better performance results in terms of directivity and peak side lobe ratio. However, the side lobes in the radiation pattern of the transmitted beam need to be reduced in order to improve the half power beam width. This article describes the simulation results obtained by comparing different windowing techniques used for beamforming of the transmitted waveform and proposes the use of the Dolph-Chebyshev beamforming technique, based on the simulation results. The usage of this technique results in an increase in the half power beam width from 26.98° to 41°, which consecutively increases the area covered by the GB-SAR system for monitoring.