How does over the horizon radar work?

Question

In relation to stealth aircraft

Answer 1

OTH radars work by literally bouncing the signal off the ionosphere.  To achieve a processable return, the transmitters must have considerable power.  Thus, OTHs are normally Early Warning/Ballistic Missile Defense systems.

There's also OTH targeting, which works by launching below the victim radar's dead-zone, (caused by earth curvature, and other terrain), a buddy is illuminating the target, acquires the missile and provides terminal guidance.  Kind of an early 80's tactic, used by the Soviets for anti-ship missions.  Now with TLAM, CALCM etc, they can basically do their own targeting.

It's not necessarily a counter-stealth technique if that's what you mean.  BUT, used in conjunction with a bi-static design, it could theoretically detect certain "stealthy" aircraft (and ships for that matter.)  A Bi-static radar has at least two geographically separate transmitters controlled by a single processing system.

Answer 2

Jim gave a good answer and I can't add anything more. .

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For what it's worth and I think at least equally interesting if you haven't heard of it, is the "deep sound channel".  

I understand the Navy uses it to communicate with it's submarines.  It's a very deep layer or band of the ocean water where sound is kept within the layer by the weight of the water above it, allowing for communications over hundreds of miles.  I believe at one time this stuff was classified.

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