It is an oversimplification to assert that deep bit depth is necessary for passive radar. In my radar class I give my students a passive raddar data set in which they can detect several aircraft (out to 100 km or so) as well as auroral electrojet irregularities (at 750 km). Initially I have them use full precision 16bit data, and then have them truncate the data all the way down to 1 bit (only the sign bit) — and it still works, with a surprisingly small sensitivity hit. [This data set came from the Manastash Ridge Radar which takes advantage of mountain range to provide significant suppression of the direct path.]

The reason for this is that passive radar data is processed with very large processing gain — about 40 dB for commercial FM, and nearly 70 dB for digital TV. Loosely speaking, passive radar detection information in range and doppler is contained not in the amplitude of the signals, but by performing appropriate correlations in the data. With other tricks, it is possible to achieve over 100 dB of instantaneous dynamic range using shallow digitizers; we’re managing that with 8 bit digitizers at the moment.

The book “Advances in Bistatic Radar” by Griffiths and Willis (2007) contains quite a bit of information about passive radar (I wrote one of the chapters, passive radar for ionospheric physics).

There will be sessions and short courses on passive radar at the May 2017 IEEE Radar Conference in Seattle.