The power P_{r} returning to the receiving antenna is given by the equation:
where
 P_{t} = transmitter power
 G_{t} = gain of the transmitting antenna
 A_{r} = effective aperture (area) of the receiving antenna; this can also be expressed as , where

 = transmitted wavelength
 G_{r} = gain of receiving antenna
 σ = radar cross section, or scattering coefficient, of the target
 F = pattern propagation factor
 R_{t} = distance from the transmitter to the target
 R_{r} = distance from the target to the receiver.
In the common case where the transmitter and the receiver are at the same location, R_{t} = R_{r} and the term R_{t}² R_{r}² can be replaced by R^{4}, where R is the range. This yields:
This shows that the received power declines as the fourth power of the range, which means that the received power from distant targets is relatively very small.
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