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The plasma sheaths generated by vehicles flying at hypersonic speed in the near space will interact with electromagnetic waves. This creates series of problems to communication and detection. Terahertz (THz) technology holds large potential in solving the problems caused by the plasma sheath for its special characteristics. However, due to the limitation in computation capability and experimental equipment, the research on the radar cross section (RCS) of the target covered with the inhomogeneous plasma sheath in THz band is still insufficient. The echo attenuation is the basis of considering the RCS attenuation, so studying echo attenuation characteristics can provide support for further study of radar scattering characteristics. In this paper, a simplified calculation method is proposed to analyze the echo attenuation characteristics of a vehicle covered with the inhomogeneous plasma sheath in THz band. Firstly, the echo attenuation model of the target covered with the inhomogeneous plasma sheath is established. Then, considering that the total echoes include the echoes reflected by the surface of the plasma sheath and reflected by the target surface through the plasma sheath, the calculation process of the total echo attenuation is derived. The variations of echo attenuation with THz frequency, plasma electron density, plasma collision frequency and incident angle are further studied. The results validate that the shielding effect of the plasma sheath is weakened in the THz spectrum. This indicates the great prospect of THz technology in the communication and detection of hypersonic vehicles in the future.
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