Enhancing security requires sensing devices surveilling over critical infrastructures for early warning of radio frequency (RF) emitter geolocations. Conventional geolocation of RF emitters has adopted active methodologies by illuminating targets, such as radar sensors. However, active geolocation draws unwanted attention of adversary, thus highly increases threats and vulnerabilities of the sensing devices. As security issues become a central concern in sensing applications, we propose a small unmanned-aerial-system for passive geolocation of RF emitters. Multiple electronic surveillance sensors are mounted on small unmanned-aerial-vehicles (UAVs) to provide geolocation awareness. Both sensors-to-UAV and UAVs-to-fusion-center communications are investigated. Different with previous studies, our approach is based on an empirical path loss and log-normal shadowing model, from a wireless communication and signal processing vision. The communication degradation from UAV to fusion center has been taken into consideration other than assuming lossless performance. The analyzed geolocation error and the error probability of distance shows that this approach provides robust performance at high frequencies, thus offers an effective solution for the security issue in RF emitter geolocation. Copyright © 2012 John Wiley & Sons, Ltd.