First Use of GPS Satellites for Beam Calibration of Radio Dish Telescopes

TL;DR

This paper demonstrates the novel use of GPS satellites for calibrating radio telescope beams, showing promising results in mapping beam structures and comparing well with simulations, thus offering a continuous and broad-frequency calibration method.

Contribution

First application of GNSS satellites for radio beam calibration, providing a new, continuous, and broad-frequency approach that complements existing methods.

Findings

GNSS satellites enable efficient 2D beam mapping.

Measured beam differences as small as 0.56 dB-Hz.

Good agreement between observed and simulated sidelobe shapes.

Abstract

We present results from the first application of the Global Navigation Satellite System (GNSS; e.g., the Global Positioning System, GPS) for radio beam calibration using a commercial GNSS receiver with the Deep Dish Development Array (D3A) at the Dominion Radio Astrophysical Observatory (DRAO). Several GNSS satellites pass through the main and sidelobes of the beam each day, enabling efficient mapping of the 2D beam structure. Due to the high SNR and abundance of GNSS satellites, we find evidence that GNSS can probe several sidelobes of the beam through repeatable measurements of the beam over several days. Over three days of measurements, the smallest observed difference in the primary beam's main lobe was 0.56 dB-Hz. We also compare our results in the sidelobes to simulations and find rough agreement in shape. When scaling the observations and simulations to match in the main lobe power levels, we find deviations in at least one of the first few nulls of approximately 5 dB or less. There is saturation in the main lobe for most satellites, which can likely be mitigated by better attenuation before the receiver input. We compare our work to other satellite systems that have been successful and are likely complementary to this technique. However, GNSS offers key advantages, including continuous transmission, broader frequency coverage relevant to CHORD, SKA-mid, and the DSA-2000, as well as more frequent satellite passes, making it a promising calibration method. These results also motivate further development of this technique for radio astronomy applications.