Radio frequency interference (RFI) in digital microwave radiometers

Here, we developed a model for determining the effects of a narrow-band RFI on low resolution digital correlators. Low resolution correlators rely on a theoretical inversion to obtain the input correlation coefficient from the digital output. This inversion is based on the Gaussian statistics of the input signals. In the presence of the narrow-band interference, the statistics are not Gaussian and the theoretical inversion is no longer valid. The result is an error in the correlator output. We studied this phenomenon for four correlator resolutions: 1, 1.5, 2, and 4 bits. The errors are significant for 1, 1.5, and 2-bit systems. We found in the presence of relatively strong interference (INR≳0 dB) the errors can be ten´s of percent. The error reduces to less than 0.03% for INR<-16 dB. For the four-bit correlators, the errors are less than 0.03% for all cases studied. The error is also nonlinearly dependent upon input correlation coefficient.