Square-law accuracy of microwave radiometers

We consider the problem of evaluating the square-law accuracy (ldquolinearityrdquo) of a microwave radiometer. In order to reduce linearity errors below the noise level, linearity error of the square law detector less than 10-4 times the linear output is needed. We derive a Volterra model of the detectorpsilas response to noise and use sinusoidal excitations to extract the kernels. By using relatively high-level signals to determine the parameters of the model, measurements near the detectorpsilas operating level are avoided and highly precise measurements are not needed. A full error analysis shows that the desired accuracy can be obtained by this method.