  The real-time unmanned aerial vehicle (UAV) trajectory design of secure
integrated sensing and communication (ISAC) is optimized. In particular, the
UAV serves both as a downlink transmitter and a radar receiver. The legitimate
user (Bob) roams on ground through a series of unknown locations, while the
eavesdropper moves following a fixed known trajectory. To maximize the
real-time secrecy rate, we propose an extended Kalman filtering (EKF)-based
method for tracking and predicting Bob's location at the UAV based on the delay
measurements extracted from the sensing echoes. We then formulate a non-convex
real-time trajectory design problem and develop an efficient iterative
algorithm for finding a near optimal solution. Our numerical results
demonstrate that the proposed algorithm is capable of accurately tracking Bob
and strikes a compelling legitimate vs. leakage rate trade-off.
