On the Optimal Antenna Beamwidth for UAV Localization using mmWave/THz Range Radars

A number of critical UAV applications such as rescue missions are performed in locations, where external positioning information is unavailable. To enable situational awareness in these use cases, millimeter wave (mmWave, 30 - 300 GHz) and terahertz (THz, 0.3-3 THz) bands range radars can be utilized. These radars are characterized by extremely high resolution. However, the small antenna aperture in these bands forces system designers to utilize massive antenna arrays to reach distances of hundreds of meters. Thus, by utilizing directional antennas, these radars need to scan the environment around a UAV detecting the location of surrounding UAVs. In this paper, by utilizing the tools of stochastic geometry we determine the optimal beamwidth required to detect all UAVs around in a minimal time. Owning to the solution complexity we also propose a simple approximation for the UAV detection probability. Our results reveal that the the use of antenna's small half-power beamwidths (HPBW) increases the successful detection probability at the expense of the scanning time. If one wants to decrease the scanning time, the only option is to decrease the radar's scanning radius. The proposed approximation is shown to introduce errors of no more than 5-8%.