noise temperature

The noise temperature is an equivalent measure of the thermal noise ofantennas and microwave receiving systems. For the noise temperature specified in Kelvin (K), two four poles are used by definition, one non-noise and one noise.

The non-noisy quadripole must produce an effective noise temperature from the input circuitry that is equivalent to that of the noisy quadripole with noise-free components at the input. The comparison of the two quad poles refers to their output noise.

If radio systems have multiple receiving components such as an antenna, the LNB converter, the antenna cable, and other mixing and amplification equipment, the noise temperature of each RF component adds up to the noise temperature of the entire receiving system.

For the antenna, the noise temperature refers to the hypothetical resistance at the input of an ideal, noise-free receiver. The output noise power produced by the amplifier is equal to that specified at the antenna output. The antenna noise temperature is composed of all noise sources in its vicinity and the antenna's own noise. The ratio of Gain to Noise Temperature (G/T) is crucial for signal processing, since increasing noise temperature is accompanied by a degradation of sensitivity.