A unified model of feed rotation in radio telescopes and GNSS antennas

TL;DR

This paper introduces a comprehensive model for phase rotation caused by feed orientation changes in radio telescopes and GNSS antennas, unifying their treatment for improved measurement accuracy in VLBI and GNSS applications.

Contribution

It extends existing GNSS phase wind-up models to include radio telescope feed rotation, enabling unified correction of phase delays in VLBI and GNSS measurements.

Findings

Validated the model with simulations and experimental data.

Produced the first phase delay solution for a specific VLBI baseline.

Demonstrated the importance of feed rotation correction in dual polarization observations.

Abstract

We describe a model that accounts for the phase rotation that occurs when a receiver or transmitter changes orientation while observing or emitting circularly polarized electromagnetic waves. This model extends work detailing Global Navigation Satellite Systems (GNSS) carrier phase wind-up to allow us to describe the interaction of changing satellite orientation with phase rotation in observing radio telescopes. This development is motivated by, and a critical requirement of, unifying GNSS and Very Long Baseline Interferometry (VLBI) measurements at the observation level. The model can be used for either stationary choke ring antennas or steerable radio telescopes observing either natural radio sources or satellites. Simulations and experimental data are used to validate the model and to illustrate its importance. In addition, we rigorously lay out the feed rotation correction for radio telescopes with beam waveguide and full Nasmyth focuses and validate the correction by observing the effect with dual polarization observations. Using this feed rotation model for beam waveguide telescopes, we produce the first phase delay solution for the VLBI baseline WARK30M-WARK12M. We provide a practical guide to using the feed rotation model in Appendix D.