Extended Data Figure 4: Antenna beam model
From: An absorption profile centred at 78 megahertz in the sky-averaged spectrum
a, Beam cross-sections showing the gain in the plane containing the electric field (dashed) and in the plane containing the magnetic field (solid) from FEKO for the H2 antenna and ground plane over soil. Cross-sections are plotted at 50 MHz (red), 70 MHz (yellow) and 100 MHz (blue). b, Frequency dependence of the gain at zenith angle Θ = 0° (solid) and the 3-dB points at 70 MHz in the electric-field plane (dashed) and magnetic-field plane (dotted). c, Small undulations with frequency, after a five-term polynomial (equation (2)) has been subtracted from each of the curves, are plotted as fractional changes in the gain. Simulated observations with this model yield residuals of 0.015 K (0.001%) to the five-term fit over the frequency range 52–97 MHz at GHA = 10 and residuals of 0.1 K (0.002%) at GHA = 0, showing that the cumulative beam yields less chromaticity than the approximately 0.5% variations in the individual points plotted.
