Square-Law Accuracy of Microwave Radiometers

We consider the problem of evaluating the square-law accuracy ("linearity") 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 detector's 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 detector's 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.