Antenna noise temperature

As a noise temperature of a Eintors the temperature is referred to, which would give a real ohmic resistance at the same noise power P available at the measurement frequency to produce as the one-port to be characterized:

It is

• B is the measurement bandwidth.

The available noise power of an ohmic resistance is up to very high frequencies proportional to the absolute temperature T, and the measurement bandwidth:

As a noise temperature of a two-port network, the noise temperature is called, which would have a connected to the gate of the two-port noise source ( noisy one-port ) to produce the same available noise power at the output of to be characterized, but then imaginary noise-free two-port network at the measurement frequency as to be characterized that noisy two-port network when driven by a noise-free imaginary source.

Low-noise amplifiers have noise temperatures of 40 K or less.

Designations

The product of temperature and Boltzmann's constant, the dimensions of energy, but also a power per bandwidth. Therefore, it is also called noise spectral power density (see the power spectral density).

At 17 ° C (290 K), it:

Multiplied by the bandwidth you get the noise power P and the above mentioned relationship.

Linear amplifiers

Ideals, linear amplifier would increase the available power of the input signal by a factor of available power gain without adding additional noise. The signal -to-noise ratio ( SNR) at the input and output would be the same.

Real amplifiers, however, are made ​​up of components which in turn noise. This means that the SNR is smaller at the outlet than at the inlet. The ratio of both SNRs leads to the noise figure:

The output signal ( ) is separated into a component which is ideally increased and a noise component that is added by the amplifier:

Where G is the gain.

If no signal ( ), the input power is determined by only the noise power, which is calculated with the above equation. The additional noise from the amplifier () corresponds to a noise temperature, which is characteristic of the amplifier, the feedback and correlation characteristics but also depends on the internal impedance of the driving source.