  In this work, an detection strategy based on multiple antennas with beam
sweeping is developed to detect UAV's potential transmission in wireless
networks. Specifically, suspicious angle range where the UAV may present is
divided into different sectors to potentially increase detection accuracy by
using beamforming gain. We then develop the optimal detector and derive its
detection error probability in a closed-form expression. We also utilize the
Pinsker's inequality and Kullback-Leibler divergence to yield low-complex
approximation for the detection error probability, based on which we obtain
some significant insights on the detection performance. Our examination shows
that there exists an optimal number of sectors that can minimize the detection
error probability in some scenarios (e.g., when the number of measurements is
limited). Intuitively, this can be explained by the fact that there exists an
optimal accuracy of the telescope used to find an object in the sky within
limited time period.
