Satellite RFI mitigation on FAST

Abstract

As the most sensitive single-dish radio telescope, the Five-hundred Aperture Spherical radio Telescope (FAST) is very susceptive to radio frequency interference (RFI) from active radio services. Moreover, due to the rapid development of space applications and research, satellite interference has become one of the main RFI sources for FAST, particularly at the L band. Therefore, we have developed several measures to mitigate satellite RFI. On the one hand, an antenna with 4.5-meter diameter has been constructed and installed at the FAST site to detect the satellite interference in the frequency band between 1 to 5 GHz. Meanwhile, we have developed a satellite RFI database based on the FAST sky coverage, the observing frequency bands, and known satellite systems. By combining the satellite RFI monitoring antenna and the database, we have established a satellite RFI mitigation system. With this system, we can not only track satellites to collect their characteristics and update the database but also help the observer to program the observing plan by predicting satellite interference. During the practical observation of FAST at the L band, the feasibility of this system to mitigate satellite RFI has been proved. In particular, the system effectively avoids strong satellite interference from entering the main beam of the telescope and causing receiver saturation.

Radio Frequency Interference Mitigation and Statistics in the Spectral Observations of FAST

“…Based on the RFI flagging process, we find that there are indeed many RFI in the FAST spectral observation (Jiang et al, 2020;Wang et al, 2021;Zhang et al, 2021b;Hu et al, 2021). We also find that some RFI are random and occasional, others are fixed at some frequencies 4 .…”

“…A number of RFI mitigation methods (e.g., Fridman & Baan, 2001;Ford & Buch, 2014;Baek et al, 2015;Wang et al, 2021;Zhang et al, 2021b;Hu et al, 2021) could be used at different stages in the data acquisition process. After collecting astronomical data, however, the only thing that astronomers can do for RFI Mitigation is to flag and eliminate the effects of known and unknown sources of RFI.…”

“…In FAST observations, there indeed exist many extremely strong and evident RFI, for example those from communication satellites and navigation satellites (Wang et al, 2021) at around 1175, 1207, 1270, and 1480 MHz (see the emission line in Fig. 1).…”

The most sensitive SETI observation by multi-beam coincidence matching strategy towards exoplanet systems

“…However, medium-Earth and geosynchronous orbit satellites are still potential RFI sources. The trajectories of satellites passing overhead during the observation can be queried by FAST satellite RFI database 30 , where we find no satellite that entered the region within 3 degrees of the main lobe of beam 1 as we observed Kepler-438. To determine whether the Kepler-438 event is a satellite signal captured by the side lobes, we can calculate the drift rates caused by the relative accelerations of the satellites and compare them with the Kepler-438 event.…”

“…2 and 3. The results of RFI test at FAST site show two main types of RFI sources within the 1.05 − 1.45 GHz frequency band: civil aviations and navigation satellites 30 . We find only a small fraction (4.2% and 3.5% for pol1 and pol2 respectively) of hits have frequencies within the civil aviation band.…”