Sugar Tree radar

Sugar Tree is the name of a bistatic over-the-horizon radar built by the US in the 1960s.^[1][2] The key idea in Sugar Tree was a reinvention of the Klein Heidelberg Nazi German passive radar system developed for use in the Second World War. Sugar Tree was a "covert hitchhiker using Soviet, surface-wave HF radio broadcast signals and a remote sky-wave receiver to detect Soviet ballistic missile launches". The key idea, in other words, is to receive radar reflections without oneself transmitting a radar signal by using instead some other signal, typically one that originates from the adversary. ^[3]

References

1. Willis, Nicholas J.; Griffiths, Hugh (2007). Advances in Bistatic Radar. SciTech Publishing. pp. 54–55. ISBN 9781891121487.
2. Chong Sze Sing, 2014. Thesis submitted to the Naval Postgraduate School, Monterey, CA. "Passive multistatic detection of maritime targets using opportunistic radar".
3. Willis, N & Griffiths, H (eds), Advances in Bistatic Radar, SciTech Publishing, Raleigh, NC 2007, cited in Willis & Griffiths " Klein Heidelberg – a WW2 bistatic radar system that was decades ahead of its time". http://www.cdvandt.org/K-H%20final.pdf