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RFI Mitigation in Time Domain Wideband Autocorrelation Radiometry (WiBAR) Using a Comb Filter

This letter presents a new hardware setup to suppress radio frequency interference (RFI) for a recently developed microwave radiometer technique, known as wideband autocorrelation radiometry (WiBAR). WiBAR is a method that can directly measure the thickness of a low-loss layer like lake ice or dry snow on the ground by finding the lag time that corresponds to the transit time of layer in the autocorrelation function (ACF) of the received signal. However, RFI increases the noise floor of the ACF and results in a decreased signal-to-noise ratio (SNR) of the WiBAR delay peak in the ACF. We enhanced a WiBAR instrument with a tunable comb filter having a frequency response with many evenly spaced alternating pass and stop bands. We show the RFI mitigation performance of a WiBAR set-up with a comb filter in the laboratory with a simulation circuit that creates a spectrum polluted with RFI.