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; classifying the moving object as one of a set of possible classes according to the extracted features; and generating an alarm signal indicating to the one selected class.