Mechanism Analysis of the Time-Frequency Flash Changes of Rotor Targets

The micro-motion in radar echoes can produce time-frequency flashes, the characteristics of which vary markedly among different targets. However, the physical mechanism governing such flash variations has not yet been fully elucidated. To address this gap, this study investigates the mechanism responsible for variations in the time-frequency flashes of rotor targets. Pronounced changes in the time-frequency flash patterns of rotor echoes are observed as the blade number or rotational speed increases. Based on the established scattering point model, the time-frequency characteristics of the echoes are analyzed using the short-time Fourier transform. On this basis, the underlying mechanism is derived, and the conditions under which the phenomenon occurs are identified. The theoretically derived conditions are validated through numerical simulations. The results indicate that an excessive rotational speed or an increased blade count causes the blades to traverse an angular interval greater than a certain range within a single slow-time interval, thereby suppressing the resolvable temporal variation in the instantaneous frequency and ultimately causing the frequency time-varying characteristics to disappear. Moreover, the STFT window length also governs the visibility and representation of the flash characteristics. Clarifying this mechanism provides a theoretical basis for aircraft target feature extraction and recognition and offers practical guidance for rotor target discrimination in practice.