Chirality and Handedness of the SKALA4.1 Antenna and Intra-Station Mitigation

Paper i proceeding, 2026

We discuss the chirality of the antenna used in the SKA-low radio telescope, called SKALA4.1. We find that it more readily accepts one circular handed radiation more than the other even along its boresight, i.e. zenith. This is in spite of the fact that vertical axis may appear at first sight to be a symmetry axis. But in fact, the mechanical structure of the SKALA4.1 antenna is not mirror symmetric, so it is a chiral antenna. This can explain its handedness preference. This can lead to a nonzero instrumental Stokes circular polarization component, also known as instrumental Stokes V. The bias in Stokes V can be difficult to calibrate and may make certain science cases more difficult. As a potential part of a mitigation strategy, we investigate the possibility of also using the specular (mirror-image) version of SKALA4.1, since the specular SKALA4.1 is found to have the exact opposite handedness of the nominal SKALA4.1. We find that mixing nominal and specular antennas does indeed decrease the beamformed bias in handedness.