CFAR Detection of Range-Spread Targets Based on the Time-Frequency Decomposition Feature of Two Adjacent Returned Signals

Radar returned signals are processed by stretch processing, resulting in mixer outputs. Based on the time-frequency decomposition of the cross S-method (CSM) of two adjacent mixer outputs, a range-spread target detector is proposed in this paper. As a preparatory work, we propose a signal synthesis method (SSM) based on the singular value decomposition. The SSM synthesizes two signals in their normalized forms from their cross Wigner distribution (CWD) and concentrates their energy on two singular values. This detector consists of three steps. First, we derive the CSM from the S-method (SM). The CSM is close to the sum of the CWDs of the components in one mixer output and their counterparts in the other. Second, we can decompose the CSM by the SSM, thereby obtaining singular values. Third, the time-frequency decomposition feature, i.e., the ratio of the sum of several biggest singular values to the median or mean of the rest, is defined to demonstrate the concentration of the singular values and used to detect the range-spread target. The proposed detector is evaluated by the raw radar data without range migration correction. Results show that it outperforms the conventional detectors. In addition, we prove that the proposed detector has the constant false-alarm rate (CFAR) property.