A Novel Frequency Tunable RF Comb Filter

This letter presents a new filter to suppress radio frequency interference (RFI) in microwave remote sensing instruments, particularly a wideband autocorrelation radiometer (WiBAR). RFI increases the noise floor and results in a decreased signal-to-noise ratio (SNR) of the WiBAR delay peak. The proposed filter operates like a Fabry-Perot interferometer (FPI) in optics and has the frequency response of a comb filter with many evenly spaced alternating pass and stop bands. The frequencies of these bands are varied with an electrically adjustable phase shifter. The design of a comb filter with an airy finesse value of 20 has been verified by simulation and measurement.