Where has the passive radar code gone?
I’m in the same industry, and find these attempts of constraining technology through secrecy extremely naive by our legislators.
I’d wager that if you already know how to operate an SDR, you properly will have little trouble with the fairly simple  algorithm of measuring phase differences, filtering, CFAR etc. to make a passive radar. Synchronizing a bag of RTL-SDRs with a common oscillator is a trivial soldering task.The cat went out of the bag the second SDRs jumped from DARPA R&D to DVB-T commodity.That aside having a passive radar breadboard is not the same as a high-end passive radar where frequency/phase stability, use of wideband multi-source emitters, ultra-low noise amplifiers and N>>2 channels for increased angular resolution are integrated in an operational system. These systems that actually works, should be controlled.