Contents I. Introduction
Passive radar is a challenging and popular topic in remote sensing area for the detection and tracking of airborne targets for a long time. The main feature and advantage of passive radar is the lack of intentional transmissions and usage of existing transmissions around for detection and tracking of targets. Passive radar concept has two main categories: Passive Emitter Tracking (PET) and Passive Coherent Locator (PCL). Although it is also called as passive radar, PET is more similar to an Electronic Support Measure (ESM) system as it uses the transmitters on the aircraft (radar, IFF, data link, and etc.) for detecting aircraft platform. Czech TAMARA, VERA, and the Ukrainian Kolchuga systems are examples for PET concept. PCL is a bi-static or multi-static radar application where the system has no transmitter but uses the illuminators of opportunity. These illuminators of opportunity may be analog TV, analog radio, digital TV, digital radio, GSM or GPS signals. Many researchers have been working on this topic for developing different applications with different illuminators. Silent Sentry (USA), CELLDAR (UK) and Homeland Alerter (France) systems are examples for PCL concept. These systems are all ground-based systems for the surveillance of airborne targets. Passive radar terminology will be used for PCL at the rest of this document.
