Sensitivity of a correlation radiometer

Abstract

The correlation radiometer is analyzed to determine the sensitivity that can be obtained under various operating conditions. The radiometer using a sine wave comparison signal is analyzed and compared with the usual radiometer that employs a random noise for the comparison signal. It is found that the radiometer employing the sine wave comparison signal is the more sensitive of the two circuits, particularly in the case that the effective temperature of the input noise signal is greater than the effective input temperature of the amplifiers. It is shown that if nonidentical amplifiers are used in the correlation circuit, the properties of the radiometer are determined by the portion of the amplifier response functions in the frequency interval that the two response functions overlap. The effect of amplifier gain fluctuations are considered, and although the correlation scheme reduces the effect of gain fluctuations, it is shown that they still do contribute to the output fluctuations of the radiometer. Calculations are included showing that the effect of a differential phase shift between the two channels is a reduction in radiometer sensitivity. The same conclusion is reached concerning the effect of a differential time delay. Finally, it is shown that if the comparison signal and the input signal have the same statistical properties, the requirements on the multiplier are less stringent than if the two signals have different statistical properties.