Passive Radar: Past, Present, and Future Challenges

From the Daventry Experiment in 1935 to the present day, passive radar technology has considerably evolved, and its range of use has expanded to include several advanced applications and complex operative scenarios. In this article, we go over some of the most relevant applications in which these sensors can be effectively employed. For each, we illustrate strategies developed to meet the peculiar challenging aspects and demonstrate the feasibility in practical scenarios by means of real-world data. Finally, based on the open issues and challenges, we reason about what the current trends and outlooks for this technology are.