This concept was invented and Engineered around 1990. This
presentation was first placed on the Internet in July 1999.|
A method for hiding American ships from enemy radar is presented. Enemy radar-guided missiles would be less successful in attacking a ship protected by this system.
In both World War I and World War II, similar vulnerability was regularly demonstrated. In World War I, German submarines easily sunk many ships with their torpedoes. In World War II, submarines and their torpedoes again took a heavy toll, but aircraft bombing also was very effective.
Modern warships are built with extremely thick steel hulls, to make them more resistant to such attacks. However, rocket based weapons are MUCH more sophisticated, as well. The example of the single Exocet missile seems clear. That one small missile disabled the ship. What would have happened if 40 such missiles has been launched at that ship? Or at a convoy of ships? Or at a battle fleet? The extremely rapid movement of the rockets and the rather slow movement of the massive ships makes them rather like sitting ducks!
Some American aircraft apply some aspects of Stealth technology. Very angular shapes is quite important in dealing with specular reflections. Think of seeing a car with a curved chrome bumper on a sunny day. This kind of surface creates almost entirely specular reflection. No matter where you are, you see a tiny but very bright reflection of the sun which gets to you. Now, imagine if that bumper didn't have that continuously curved surface, but rather just flat surfaces with sharp edged corners. Now, nearly anywhere you are, you will not see ANY reflection of the sun off of it! It turns out that the boxy shape tends to make ALL the reflection go to one very specific direction, with almost no specular reflection going anywhere else. You may have noticed some flat truck windshields that almost blind you with the reflection, but only when you are at a very specific position.
As applied to radar, as long as the specular reflection is all reflected in ANY OTHER DIRECTION than back to the originating radar station, no specular echo will ever be received, and so the object will be essentially invisible on radar. I had a big, old, ugly, 1972 Ford Van, that I considered modifying as an experiment around 1984. On the front of it, I considered mounting a giant flat (specularly-reflective) metal mirror, with the lower edge farther forward than the top. So it would have sort of looked like a sloped-back wedge from the front! This would have specularly reflected ALL radar signals upward into space, with NONE ever being reflected back to a radar gun. This would have made the big vehicle effectively invisible on Police Radar! (Essentially, only exposed surfaces such as the tires could still reflect radar signals back to a radar gun, but that reflection would be very minimal, comparable to the radar echo off of a dog-sized object. Most radar guns have a sensitivity adjustment where such weak echoes are ignored.)
Of course, as soon as the mirror got even a little dirty, it would then ALSO create DIFFUSE reflection, which WOULD cause a relatively weak echo to get back to an originating Police Radar, so the premise is impractical there. American stealth aircraft have angular shapes for the exact same reason as described above. They deal with minimizing diffuse reflections by using special coatings (paint) to absorb rather than reflecting those wavelengths. By combining the two types of technologies, those aircraft suppress both specular and diffuse reflection, and therefore accomplish virtual invisibility on enemy radars.
It is briefly necessary now to discuss an entirely different subject. There are some industrial sound-protection safety earmuffs, that are high-tech. Instead of just trying to muffle sounds that approach a person's ears, these products have a microphone to sample the incoming sounds. They then appropriately amplify AND INVERT the signals. It might first seem that the user would then be subjected to TWICE the loudness of the incoming sounds, but that is not true. By precise synchronization of the artificially created inverted signal, the result is that the two loud sound sources cancel each other out, eliminating virtually all of the sound! These hearing-protection devices have become quite common in industry, with current prices of a few hundred dollars.
These products are based on a very well established Physics concept called "destructive interference of waves" Two (traveling) wave patterns which are identical and exactly out of phase with each other will cancel each other out, leaving nothing remaining!
The proposed Ship Stealth invention is based on the same concept. Instead of sound waves, we would be dealing with radar waves, which are equally subject to being cancelled out by the addition of an inverted duplicate signal. The main difference is that sound waves travel relatively slowly (at the speed of sound) while radar waves travel about a million times faster, at the speed of light. Other than that, the situations are quite similar.
The result of this is an almost complete cancellation of the echo from the actual ship structure! The radar installation that sent out the radar beam would NOT receive an echo with which it could become aware of the ship's presence!
If the extended boom antennas (possibly with the electronics immediately there, for faster processing) extended out 20 feet beyond the ship body, then around 20 nanoseconds would occur before the incoming radar signal actually hit the ship body, and another 20 nanoseconds would pass while the radar echo traveled back to where the antenna was. At that time, the artificial (inverted) radar echo should begin to be emitted, to cancel out that echo.
For any real computer, with real circuit wires and antenna, this rapid of a response may not be possible. Signals cannot move in wires any faster than the radar signals and echoes move through the air. The computer processing time would almost certainly make it so that at least the first small part of the radar echo would not be able to be cancelled and so it would actually be reflected back to the radar installation. However, as long as the bulk of the echo was nulled out, the received echo would appear to be the echo from a very small boat, rather than from a large ship.
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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago