Very interesting, thanks for sharing. I'm curious about the following:

(1) Seems like these very challenges also make the space more interesting because not everyone can make a good passive radar system and the passive aspect obviously provides stealth (not to the plane, but to the party doing the surveillance). Is this fair to say? (2) What if there are multiple receivers in clock sync? Does that make it easier? (3) I'm a bit confused about your comment about very large antennas -- I thought antenna size should be proportional to the wavelength. So if the system is using digital TV broadcast, then the antenna size would be roughly the size of DTV antennas, and bigger would not necessarily help? Or is this not the case? (4) Re the ionopheric issues -- do the clouds or ionophere reflect the TV/fm waves? I thought each tx-target-rx triplet having a different delay would be a good thing because it would dismbiguate multiple targets.