Limits on Unintended Radio Emission from Geostationary and Geosynchronous Satellites in the SKA-Low Frequency Range

TL;DR

This study uses MWA data to set upper limits on unintended radio emissions from geostationary satellites, providing a baseline for future interference monitoring relevant to the SKA-Low telescope.

Contribution

First to systematically search for and establish upper limits on unintended radio emissions from GEO satellites in the 72-231 MHz range.

Findings

No evidence of unintended emissions detected from GEO satellites.

Achieved upper limits below 10 microWatts EIRP for most satellites.

Provides baseline data for future interference monitoring efforts.

Abstract

We search data from the GLEAM-X survey, obtained with the Murchison Widefield Array (MWA) in 2020, for the presence of radio frequency interference from distant Earth-orbiting satellites, in the form of unintended emissions similar to those recently seen from objects in Low Earth Orbits (LEO). Using the GLEAM-X Dec = 1.6 degree pointing, which is stationary in azimuth (on the local Meridian) and elevation (near the celestial Equator), the very wide field of view of the MWA maintains custody of a large number of satellites in geostationary and geosynchronous (GEO) orbits in this direction for long periods of time. We use one night of GLEAM-X data in the 72 - 231 MHz frequency range to form stacked images at the predicted coordinates of up to 162 such satellites, in order to search for unintended radio emission. In the majority of cases, we reach 4 sigma upper limits of better than 1 mW Equivalent Isotropic Radiated Power (EIRP) in a 30.72 MHz bandwidth (dual polarisation), with the best limits below 10 uW. No convincing evidence for unintended emissions at these detection thresholds was found. This study builds on recent work showing an increasing prevalence of unintended emissions from satellites in LEO. Any such emission from objects in GEO could be a significant contributor to radio frequency interference experienced by the low frequency Square Kilometre Array and warrants monitoring. The current study forms a baseline for comparisons to future monitoring.