We propose a two stage detector consisting of a Subspace Detector (SD) followed by the Whitened Adaptive Beamformer Orthogonal Rejection Test (W-ABORT). The performance analysis shows that it possesses the Constant False Alarm Rate property with respect to the unknown covariance matrix of the noise and that it guarantees a wider range of directivity values with respect to previously proposed two stage detectors. The probability of false alarm and the probability of detection (for both matched and mismatched signals) have been evaluated in closed form.