This paper presents a calibration technique for phased array radars. The real embedded patterns of the array elements are measured independently in operating mode, while taking antenna coupling and other parasitic effects into account. The proposed technique does not affect the operation of the antenna array. The use of suitable switches integrated in the beamforming network of the array allows introducing sparsity into the measured summed signal. This enables the extraction of the angular dependent calibration coefficients by means of a dedicated compressed sensing approach.