Impact of Half-Angles on the Transmission of Terahertz Wave in Inhomogeneous Plasma Sheath

Terahertz communication is considered as a potential solution to alleviate the communication blackout. However, it is not clear how the shape parameters of the vehicle affect the propagation of terahertz communications in the plasma sheath. In this article, the influence of half-angle on the plasma flow and terahertz propagation characteristics around blunt cone vehicle was investigated using the numerical hypersonic hydrodynamic model and multilayer transmission model. The maximum electron number density in the plasma sheath near the antenna decreases with the decreasing half-angle. The thickness of the high-density section in the plasma sheath is almost unaffected by the half-angle. As a result, the terahertz wave attenuation decreases with the decreasing half-angle. The half-angle is reduced from 20° to 5°, and the attenuation of electromagnetic waves is reduced by about 25 dB. Therefore, reducing the half-angle of blunt cone vehicle can effectively reduce the attenuation of electromagnetic waves. Finally, the feasibility of lowering the half-angle to solve the blackout problem during the whole reentry process was discussed; the results show the operating frequency of terahertz wave that maintains normal communication when the half-angle is 1° is reduced by 0.1 THz compared with the half-angle of 9°. Based on the study, a new scheme combining the reduction of half-angle of blunt cone vehicle and terahertz communication was proposed in this article to mitigate the RF blackout.