Mitigation of Radar Interference in L ‐Band Radio Astronomy

Abstract

The 1215-1400 MHz band is important for spectroscopy of H I at highredshift, pulsar work, and SETI. Observations at these frequencies arecomplicated by pulsed interference from ground-based aviation radars. Inthis paper, we characterize one such radar received at the AreciboObservatory using coherently sampled data sets obtained during a recentobservation. Using these data, we demonstrate some simple methods fordetection and removal of the radar pulses. One of these uses a coherentsubtraction technique that has not previously been applied to the radarproblem. This new technique provides an alternative to blanking, whichis undesirable in pulsar and SETI work. We demonstrate that the radarstudied in this paper can be suppressed by at least 16 dB in integratedspectra using the coherent subtraction technique. The maximumsingle-pulse power observed at the output of the canceler is ~15 dBless. The primary limitation appears to be the detector performance; asa result, the performance using blanking is about the same. Also, wedemonstrate that the matched detector for pulses from this radar isrelatively insensitive to astronomical transients (e.g., giant pulses),and we quantify the risk of such transients being falsely identified asradar pulses. The techniques described in this paper can easily beadapted to radar waveforms other than the one examined here.