Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 30

For an amplifier under test, the noise power at the output, relative to the kTB noise power, is called the excess noise power, P_NE, and is computed as

(1.66)

For a matched source and load, it is the excess noise, above kTB, that is measured in the terminating resistor and can be computed as

(1.67)

which is sometimes called the incident relative noise or RNP_I (as opposed to available, or RNP). Errors in noise figure measurement are often the result of not accounting properly for the fact that the source or load impedances are not exactly Z₀. A related parameter is the operating temperature, which is analogous to the input noise temperature at the amplifier output, and is computed as

(1.68)

While the effect of load impedance may be overcome with the use of available gain, which is independent of load impedance, the effect of source impedance mismatch must be dealt with a much more complicated way, as shown next.