I. Introduction
The beginnings of passive radar date back to the 1930s, when Sir Robert Watson-Watt was able to detect a Heyford bomber from a distance of about eight kilometers and track it for about 13 kilometers in the United Kingdom using the illumination of the BBC Empire shortwave transmitter in Daventry. Since then, a lot has happened both technically and in terms of applications. The use of passive radar is no longer limited to military applications, but extends from studies of ionosphere physics to supplementing air traffic management or surveillance and disaster control tasks [1].