Analysis on ISAR image displacement of Plasma-Sheath-Enveloped Reentry Vehicle

The plasma sheath enveloping the surface of reentry vehicle can cause parasitic modulation on electromagnetic waves in amplitude and phase. When performing ISAR imaging on reentry vehicle, the radar echoes will also be affected. Due to its high-speed and fluid characteristics, the plasma has non-uniform velocity distribution. High-velocity scattering points in plasma sheath will induce mismatching of radar echoes' pulse compression, resulting in not only peak position offset in one-dimensional range profile, but also ISAR image displacement on range dimension. In this paper, through analyzing the distributions of electron density and flow velocity of the plasma sheath, we deduce the echo model of plasma-sheath-enveloped reentry vehicle. By calculating the relationship between the peak position offset in one-dimension range profile and the flow velocity of scattering point with different radar parameters, we reveal the mechanism of ISAR image displacement on range dimension. Simulations results suggest that the phenomenon of ISAR image displacement can be significantly alleviated by either minimizing the carrier frequency and pulse width or increasing the bandwidth and the echo delay or both.