A preliminary Doppler analysis in the UHF-band on a man walking in free space is presented in this paper. Firstly, the back-scattered response of the moving target has been provided at 1 GHz by a simulation tool based on physical optics theory. Then, a short-time Fourier transform (STFT), a reassignment spectrogram (RE-Spect) and a Wigner-Ville distribution (WVD) have been employed to the data, in order to characterize the micro-Doppler signature of the human body walking. The results are based entirely on numerical tests. The investigation on the time variations of the Doppler spectrum of moving targets in UHF-band is of interest for the emerging radar applications devoted to the detection and tracking of people in highly cluttered environment.