Model and Method Used for Extraction of Projectile Motion Information from Radar Echo

For a projectile with slots at the base, the index of amplitude modulation in Doppler radar echo reflects the information of angular motion. According to our research, the procedure to obtain the index can be divided into two steps, i.e., 1) separating the envelope from radar echo and 2) estimating the index from the acquired envelope. Here we assume that the envelope has already been achieved. To obtain the index from the envelope so as to extract the motion information, we investigated first the signal model of the envelope. A constant envelope model of echo is modified as an amplitude modulation and frequency modulation signal to express the amplitude modulation. The envelope is simplified as the combination of DC, the component of spin rate, and the second harmonic of spin. To restrain long-range and short-range spectral leakages and improve the index estimation accuracy, an interpolated FFT method that iterates in frequency domain and time domain alternately is proposed to. It adopts the interpolation algorithm in frequency domain to alleviate short-range leakage effect, uses the time window and the iterative CLEAN technique to realize long-range leakage correction. The influences of such parameters, as modulation frequency, value of the index, and SNR are simulated. The results of simulation and experiment prove the rationality of the model and the validity of the proposed method.