A radiometer in which independent thermal signals are combined to form first and second receiver channel input signals that are coherent with respect to each other. The first and second receiver channel input signals are independently processed in parallel receiver channels to provide first and second correlation signals, each of which include a thermal signal component and a noise signal component. The first and second correlation signals are then correlated to provide an output signal for the radiometer. If, in the combination of the independent first and second thermal signals to form the first and second receiver channel input signals, the portion of the first thermal signal included in one of the receiver channel input signals is quadrature phase shifted with respect to the portion of the first thermal signal included in the other receiver channel input signal, and, similarly, the portion of the second thermal signal that is included in the other receiver channel input signal is quadrature phase shifted with respect to the portion of the second thermal signal included in the one receiver channel input signal, an improvement in the radiometer sensitivity is realized. Alternatively, if the portion of the first thermal signal included in one receiver channel input signal is phase shifted one hundred eighty degrees with respect to the portion of the first thermal signal included in the other receiver channel input signal, the radiometer will discriminate between the independent thermal signals.
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