1. A method for classifying a moving object using microwaves, comprising: transmitting, by a linear array of transmit antenna elements, a microwave into a surveillance area; receiving, by a linear array of receive antenna elements, a scattered microwave backprojected from a moving object; extracting features from the scattered microwave related to a spiral evolution of the scattered microwave, in which the features are extracted using a sliding time-window, in which the sliding window includes N samples x 1 , x 2 ,. .. , x N , where x 1 is a first sample, and X N is a last sample for any instance in time, and in which the features are a total curvilinear distance traversed as a result of the scattered microwave, expressed as CURVD = ∑ i = 2 N ⁢ ⁢ ( x i - 1 - x i ) 2 ; classifying the moving object as one selected class of a set of possible classes according to the extracted features; and generating an alarm signal indicative of the one selected class.