P. Krueger, M. Ruiter, S. J. Wijnholds and M. A. Brentjens, "RFI mitigation strategies for next generation phased array radio telescopes," URSI Asia-Pacific Radio Science Conference (AP-RASC), New Delhi (India), 9-15 March 2019.

The Low-Frequency Array (LOFAR) telescope is a phased array radio telescope that observes weak astronomical signals in-between strong terrestrial radio frequency interference (RFI). The RFI causes intermodulation products in the analog system due to the non-linearity of the electronic devices used. Multiple strategies are implemented in LOFAR to mitigated the RFI and their intermodulation products: RFI is suppressed in the analog domain based on their direction-of-arrival, using analog beamforming, and based on their frequency, using notch and bandpass filters. The intermodulation products are minimised by using a very linear signal chain, using several stages of low-gain, high-linearity amplifiers. However, in some LOFAR observations, the intermodulation products add in-phase during beamforming, limiting the sensitivity of the telescope. It is shown how this can be prevented by adding different time delays to each signal before digitisation.

back to publication list