Abstract:  Aiming at the problems of radar signal attenuation, dispersion and blackout caused by the plasma sheath during the reentry of hypersonic vehicles, this paper derives the equivalent permittivity, electromagnetic wave attenuation and dispersion factors of the plasma based on unmagnetized thermal plasma and electromagnetic wave theories. A simplified reflection model is established for a perfectly conducting substrate covered by a single-layer uniform plasma, and the blackout zone is divided according to the reflection coefficient and the propagation attenuation threshold. A radar echo model for the plasma-sheath-enveloped target is constructed, and simulations are carried out to study the attenuation, modulation, identification, detection and probing issues. The results show that the simplified model agrees well with the numerical simulation. The plasma sheath can be identified by the waveform entropy discrimination and the alternating wide‑and‑narrow pulse envelope method. The positive‑and‑negative slope chirp signals can effectively suppress the range‑Doppler coupling, while the phase‑coded signals exhibit better low‑sidelobe performance and stronger anti‑broadening capability. The research findings can provide a reference for radar reflection modeling, attenuation analysis and waveform optimization in the blackout region.