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This paper presents the implementation of a Fresnel zone to far field transformation algorithm for the measurements of the main patterns (E and H plane) of separable array antennas, from the acquired field values in those main patterns. The method is based on the Fourier Series decomposition of the 1/R2 term of the field propagation in spherical coordinates. This method is valid for Fresnel Zone Measurements, where the 1/R3 term can be neglected. The Antenna Test Facility of the Technical University of Madrid (LEHA-UPM) is using this method for characterizing the BTS antennas for GSM and UMTS cellular systems. These antennas have dual linear polarization (±45°), several antenna ports (depending on the antenna design) and a controlled electrical downtilt, typically from 0° to 14°. Antenna manufacturers and cellular companies are normally interested in the radiation pattern for the main planes, so this method is applied to reduce drastically the acquisition time with accurate results.