Welcome to Onera, the French Aerospace Lab

The advantages

• The frequency of the signals used is lower than that of traditional radars: FM radio (88-108 MHz) and television (400 to 800 MHz). Now, the lower the frequency the larger the surface that the target seems to have. Therefore, the system is  suitable for detecting small flying objects.
• The lower frequency of the signals and their limited range in relation to traditional radar orients these systems towards the detection of slow moving and low flying targets, which may be characteristic of stealth intrusions.
• The absence of active transmission gives the system a stealth character that is suited to the surveillance of frontier areas.
• There are no electromagnetic compatibility problems.
• Finally, the limits imposed by the regulations on the ranges of the electromagnetic spectrum allocated to radar applications favor the use of this method.

The difficulties

• The multiple reflections and compensations that make signal processing more complex.
• The computing power necessary. Although the principle of passive radar has been known since the 1920s, extracting the signal has remained an insurmountable problem before the recent increase in computing power. With 100 GFlops, or one hundred billion floating point operations per second – the computing power that has become available in the last three or four years - signal processing in real time has become a possibility. 
• The change in TV and radio signals from analog to digital modifies the computational analysis but opens up new possibilities.

Industrial development
There are not yet many industrial players in this emerging field. But the situation may change quickly.