Scattering of UAV Swarm via Artificial Plasma Cloud for Probable Over-the-Horizon Detection at VHF Band

The metal vapor, released in the upper atmosphere, generates an artificial plasma cloud. It acts as a scatter to tailor radio propagation. In this paper, the compound scattering of an unmanned aerial vehicle (UAV) swarm via the artificial plasma cloud is studied and its application in over-the-horizon detection is explored for the first time. Firstly, the hybrid technique of the uniform geometric theory of diffraction (UGTD) and High Frequency Structure Simulator software (HFSS) is introduced for different parameters, such as the large scene of clouds, sizes of UAVs and wavelengths at VHF band. For radio frequency in the range of 30-70 MHz, it is found that the received power shows a decreasing trend with increasing radio frequencies. Compared with a single UAV, the received power for a UAV swarm is ~20 dB higher, though the fluctuation in radar cross sections (RCSs) due to the superposition of swarm factor. Therefore, the optimum radio frequency for the over-the-horizon detection could probably be raised from the commonly used HF band to a new VHF band. It is attractive that the UAV swarm could be detected over-the-horizon via an artificial plasma cloud at VHF band for meter-level RCS targets. It could also compensate adverse effects of HF band due to ionospheric disturbances especially in the maritime environment or emergency scenarios.