The plasma sheath will be generated on the surface of the reentry object due to the effect of aerodynamic thermoionization, causing multicomponent signals with Doppler frequency components in the radar echo. This situation will further result in the appearance of false targets that seriously affect the detection of reentry targets by radar, causing positioning errors and even tracking losses. In this article, the echo signal model of the plasma sheath covered reentry target is established, and the multidomain characteristics of the echo signal in terms of time, time-frequency, and range are analyzed, revealing the influence mechanism of plasma sheath on radar detection of reentry target. Through range-period analysis, the influence of intrapulse Doppler frequency caused by plasma sheath is determined as well as the interpulse Doppler frequency on target range measurement. Theoretical analyses conducted in this study are verified by simulation results, laying theoretical foundation for effective detection and reliable tracking of plasma sheath covered reentry targets.

The high velocity of the re-entry object causes its surface to be enveloped with a plasma sheath. In the process of target detection of re-entry objects, the plasma sheath with fluid characteristics results in multiple reflected signals in the radar echo. Multiple targets appear in the 1-D range profile following pulse compression processing of a multicomponent echo signal. We refer to targets different from the real target as interference targets. The appearance of interference targets seriously affects the radar detection of re-entry objects, resulting in positioning failure or even tracking loss. In this article, by establishing the physical model of radar echo with multiple reference points and multiple velocity parameters of the re-entry object under plasma sheath, the multitarget phenomenon of the re-entry target echo signal on the 1-D range profile is simulated. A target detection method based on Doppler frequency compensation and nonuniform plasma sheath reflection model is proposed, which can effectively suppress false targets and realize reliable detection of targets under plasma sheath. The feasibility of detecting a target enveloped by a plasma sheath is verified by simulation, laying the foundation for the precise detection and tracking of targets.

The radar echo signal of a high-speed target is simulated in this letter. Using the Lorentz transformation, the linear frequency modulation (LFM) pulse radar signal is transformed from the laboratory coordinate system into a moving system. The near-zone scattered fields and far-zone echo signals are solved by the Finite Difference Time Domain (FDTD) algorithm in the moving system kept the same speed with the target. Subsequently, transform the echo signal back to the laboratory system. Meanwhile, this letter combines the graphic processing unit (GPU) parallel technique with the Lorentz-FDTD method to realize the simulation of a high-speed target excited by a large time-width signal and extracts the range profile of the target. The validity of the proposed method is verified by the analytical results of a uniformly moving target excited by arbitrary directions incident waves. Numerical examples show that the motion's effects on the distance information of the radar signal are nonnegligible for high-speed objects.

When a near-space hypersonic vehicle flies at a velocity of several Machs, a plasma sheath is created on its surface. The plasma sheath is a complex electromagnetic (EM) medium composed of many charged particles, producing a series of EM effects on EM waves. In this article, based on the numerical calculation results of the plasma sheath flow field at typical altitudes, the spatial distribution characteristics of the reflection intensity of the typical reference area on the vehicle surface are solved. The EM shielding effect of the plasma-sheath-covered target is revealed by the incident depth and the maximum reflection position of the EM wave in the plasma. By analyzing the influence of different flight altitudes and carrier frequencies on the reflection characteristics of each typical vehicle area, the variation law of the EM shielding effect of the plasma-sheath-covered target is obtained. The research results reveal the EM shielding mechanism of plasma sheath and provide a theoretical basis for radar detection and radar cross section (RCS) measurement of the plasma-sheath-covered target.

When the reentry target passes through the earth’s atmosphere, its surface is covered with a layer of plasma sheath. In the process of radar detection of the reentry target, the echo signal will couple with multi-Doppler frequency components and form multiple mismatch effects with matched filter, which will produce false targets on the 1-D range profile. Meanwhile, the excessive speed of the reentry target will lead to the phenomenon of migration through range cells (MTRCs), which will further affect the detection and recognition of the target. This article proposes an improved frequency-domain compensation method that aims at false target and cross-range unit migration. By constructing the intrapulse Doppler frequency and interpulse Doppler frequency compensation functions, the multiperiod echo signal is processed to eliminate the MTRC phenomenon and improve the energy gain of the real target. Finally, the feasibility of the proposed algorithm is verified by simulation, which lays a theoretical foundation for the effective detection and reliable tracking of plasma-sheath-covered targets.

Due to the high velocity of hypersonic target, the target surface is covered with plasma sheath. For radar detecting on hypersonic target, the spatial distribution characteristics of plasma sheath cause significant differences in echo intensity and frequency offset at different areas of the target surface. In order to further investigate the reflection characteristics of each area of the target, this study adopts a difference-equivalent transmission line method to calculate the distribution characteristics of reflection intensity of the plasma-sheath-covered target and reveals the coupling mechanism of intrapulse Doppler frequency of the reflected wave by utilizing frequency offset effect. First, based on numerical calculation results of surface flow field, we analyzed the spatial distribution characteristics of the electron density and velocity of the plasma sheath. Second, we obtained the influence laws at different altitudes and carrier frequencies on the reflection intensity distribution and frequency offset of the plasma-sheath-covered target in each area. Finally, by constructing 1-D range profile of target radar echo, we further revealed the influence mechanism of the reflection characteristics of plasma-sheath-covered target on radar detection. Our research results lay a solid theoretical foundation for calculating the scattering characteristics of plasma-sheath-covered targets, reliable and robust radar detection, and even electromagnetic (EM) stealth performance under active modulation.