Topcat47
Well-Known Member
Ignorance is no bar to having an opinion.
The "Radar Reflectors" tested by QinetiQ were tested in an anechoic chamber, in isolation, so that their responses could be accurately assessed. These are effectively enhancements to the radar signature of the vessel to which they are attached.
All reflectors other than the Visible, the Cyclops and the Tri-lens are variations of a corner reflector, even the carpet plastic tubes.
The tube reflectors have bi-fold corners and will only return any echo when the incident waves are at 90 degrees to the corner, which is why they are so ineffective.
Other corner reflectors have either "stacked arrays" inside a cover (like the Blipper) where the corners are facing different directions, or planar like the folding ones that have to be arranged in the "catch water" position in order to give a good return. These are corners in three dimensions and the principle of these is to reflect as much of any incident wave back in the direction from which it came. The maximum return is when the incident wave is co-planar to the axis of symmetry of the corner. If you study the polar plots of the strength of the echo, they form a teardrop along this axis, fading as the direction varies.
Lens reflectors are designed to focus incident radar waves and reflect them back in the direction from which they came, which is why the give such consistent echoes. These are maximised across polar arcs of around 120 degrees, which is why the Tri-lens has three.
When a radar pulse strikes a target, how much of the incident radiation is reflected back to the transmitting antenna depends on the nature of the target. Ships are largely made of steel which give good consistent echoes and local effects can generally be ignored. No operator is going to miss a Hapag -Lloyd container ship because it's return varies between 1000 and 1200 square meters due to the various lumps of oddly shaped metal strewn around it's decks. Leisure craft are made largely from Fibre reinforced plastic, which is relatively transparent to radar frequencies and tend to absorb radiation rather than reflect it. Furthermore, any radar return from, say, a Westerly Centaur will vary due to it's relative instability, and the scattering effect of the metal items such as masts, anchors, booms and rigging. In calm conditions the variation will be slight, so there will be some consistency regarding the return, but in confused conditions there will be little consistency from the return and it will likely be lost in general clutter at the receiver, particularly if the sensitivity control of the display has been used to eliminate spurious echoes.
All reflectors have different performances depending on the frequency band used by the radar being tested. One that presents a good radar cross section to an X-Band radar will present a different one at S-Band.
The "Radar Reflectors" tested by QinetiQ were tested in an anechoic chamber, in isolation, so that their responses could be accurately assessed. These are effectively enhancements to the radar signature of the vessel to which they are attached.
All reflectors other than the Visible, the Cyclops and the Tri-lens are variations of a corner reflector, even the carpet plastic tubes.
The tube reflectors have bi-fold corners and will only return any echo when the incident waves are at 90 degrees to the corner, which is why they are so ineffective.
Other corner reflectors have either "stacked arrays" inside a cover (like the Blipper) where the corners are facing different directions, or planar like the folding ones that have to be arranged in the "catch water" position in order to give a good return. These are corners in three dimensions and the principle of these is to reflect as much of any incident wave back in the direction from which it came. The maximum return is when the incident wave is co-planar to the axis of symmetry of the corner. If you study the polar plots of the strength of the echo, they form a teardrop along this axis, fading as the direction varies.
Lens reflectors are designed to focus incident radar waves and reflect them back in the direction from which they came, which is why the give such consistent echoes. These are maximised across polar arcs of around 120 degrees, which is why the Tri-lens has three.
When a radar pulse strikes a target, how much of the incident radiation is reflected back to the transmitting antenna depends on the nature of the target. Ships are largely made of steel which give good consistent echoes and local effects can generally be ignored. No operator is going to miss a Hapag -Lloyd container ship because it's return varies between 1000 and 1200 square meters due to the various lumps of oddly shaped metal strewn around it's decks. Leisure craft are made largely from Fibre reinforced plastic, which is relatively transparent to radar frequencies and tend to absorb radiation rather than reflect it. Furthermore, any radar return from, say, a Westerly Centaur will vary due to it's relative instability, and the scattering effect of the metal items such as masts, anchors, booms and rigging. In calm conditions the variation will be slight, so there will be some consistency regarding the return, but in confused conditions there will be little consistency from the return and it will likely be lost in general clutter at the receiver, particularly if the sensitivity control of the display has been used to eliminate spurious echoes.
All reflectors have different performances depending on the frequency band used by the radar being tested. One that presents a good radar cross section to an X-Band radar will present a different one at S-Band.
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