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The dish has a radius that equals the diameter of the cylinder it is attached to (=). The knuckle has a radius that equals a tenth of the diameter of the cylinder ( r 2 = 0.1 × D o {\displaystyle r_{2}=0.1\times Do} ), hence its alternative designation "decimal head".
All units used for the radius, focal point and depth must be the same. If two of these three quantities are known, this equation can be used to calculate the third. A more complex calculation is needed to find the diameter of the dish measured along its surface. This is sometimes called the "linear diameter", and equals the diameter of a flat ...
The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it has high directivity . It functions similarly to a searchlight or flashlight reflector to direct radio waves in a narrow beam, or receive radio waves from one particular direction only.
Porringer – a shallow bowl, 4–6 inches (10–15 cm) in diameter, and 1.5–3 inches (3.8–7.6 cm) deep; the form originates in the medieval period in Europe and they were made in wood, ceramic, pewter and silver. A second, modern usage, for the term porringer is a double saucepan similar to a bain-marie used for cooking porridge.
Offset dish antennas are more difficult to design than front-fed antennas because the dish is an asymmetric segment of a paraboloid with different curvatures in the two axes. Before the 1970s offset designs were mostly limited to radar antennas, which required asymmetric reflectors anyway to create shaped beams.
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Solar parabolic dish. With a parabolic dish collector, one or more parabolic dishes concentrate solar energy at a single focal point, similar to the way a reflecting telescope focuses starlight, or a dish antenna focuses radio waves. This geometry may be used in solar furnaces and solar power plants.