DESIGN AND IMPLEMENTATION OF RECEIVER SYSTEM FOR SUPPPRESSING RADIO FREQUENCY INTERFERENCE USING ADAPTIVE FILTERS

摘要

Radio Frequency Interference (RFI) is increasingly affecting radio astronomy observations. Recent interference mitigation techniques developed for communication engineering have been applied in radio astronomy. However, RFI rejection achieved till now is not sufficient for radio astronomy. Research in developing new techniques is therefore essential. This paper describes an improvised technique of RFI suppression by adaptive filters by constraining the bandwidth of the reference signal and also to study the effects of quantisation of bits to suppress RFI. The adaptive cancellation technique requires two receivers: a primary channel that will be the radio telescope and a reference channel. For this experimental research, a reference receiver system has been designed and built which could be used along with the existing 10.4m diameter radio telescope functioning at Raman Research Institute, Bangalore. The receiver setup is designed around the 1.4 GHz receiver system of the 10.4-m telescope, and thus the research is to mitigate RFI in the 1.4204 GHz frequency band. The reference antenna system constructed is used to receive the man made RFI .The bandwidth of the reference signal is reduced by 25 MHz and then is processed by an adaptive filter .The 1.4 GHz signal from the telescope and antenna are down converted to 50MHz and connected to a data recording system. By simulations in Matlab, we studied the effect of constraining the bandwidth of reference signal on the suppression achieved in a LMS adaptive filter when the signal to noise ratio of the RFI in the reference channel is moderate. It is found that constraining the bandwidth.