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Friis formula or Friis's formula (sometimes Friis' formula), named after Danish-American electrical engineer Harald T. Friis, is either of two formulas used in telecommunications engineering to calculate the signal-to-noise ratio of a multistage amplifier. One relates to noise factor while the other relates to noise temperature.
The Friis transmission formula is used in telecommunications engineering, equating the power at the terminals of a receive antenna as the product of power density of the incident wave and the effective aperture of the receiving antenna under idealized conditions given another antenna some distance away transmitting a known amount of power. [1]
Harald Trap Friis (22 February 1893 – 15 June 1976), who published as H. T. Friis, was a Danish-American radio engineer whose work at Bell Laboratories included pioneering contributions to radio propagation, radio astronomy, and radar. [1]
The FSPL is rarely used standalone, but rather as a part of the Friis transmission formula, which includes the gain of antennas. [3] It is a factor that must be included in the power link budget of a radio communication system, to ensure that sufficient radio power reaches the receiver such that the transmitted signal is received intelligibly.
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A type of antenna that combines a horn with a parabolic reflector is known as a Hogg-horn, or horn-reflector antenna, invented by Alfred C. Beck and Harald T. Friis in 1941 [20] and further developed by David C. Hogg at Bell Labs in 1961. [21] It is also referred to as the "sugar scoop" due to its characteristic shape.
In its simplest form, the path loss can be calculated using the formula L = 10 n log 10 ( d ) + C {\displaystyle L=10n\log _{10}(d)+C} where L {\displaystyle L} is the path loss in decibels, n {\displaystyle n} is the path loss exponent, d {\displaystyle d} is the distance between the transmitter and the receiver, usually measured in meters ...
The noise factor (a linear term) is more often expressed as the noise figure (in decibels) using the conversion: = The noise figure can also be seen as the decrease in signal-to-noise ratio (SNR) caused by passing a signal through a system if the original signal had a noise temperature of 290 K. This is a common way of expressing the noise ...