Submarine Platforms
Submarines are the original stealth platforms. When no more than a mast breaks the surface, they immediately become radar targets, so virtually all modern submarines will have the minimum ELINT of a radar warning receiver. Far beyond that, however, many submarines will penetrate hostile areas, raise SIGINT receiver masts, usually with some type of radar-observant covering, and listen. Especially sophisticated SIGINT submarines may tap undersea cables.
The minimum radar-warning receiver is usually a set of spiral antennas, backed with resonant cavities, whose amplitude can be compared to determine the direction of greatest signal strength. To go to the next level of sophistication, phase is considered as well as amplitude, and interferometry adds further information.
Read more about this topic: Signals Intelligence Operational Platforms By Nation
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