Voltage beam and aperture maps for the HBA at 139 MHz derived from the observation L658168. Top left: amplitude of the voltage beam. Top center: beam model amplitude. The beam model is generated using the derived phases for the stations in the AUT. Top right: amplitude of the residuals after subtracting the beam model from the observed voltage beam (top left). Bottom left: aperture map obtained by taking the Fourier transform of the voltage beam (inverse Fourier transform of Eq. (2)). The white circles show the location of the stations in the AUT. Bottom right: amplitude of the Fourier transform of the beam residuals (top right).