Mitigating Zenith Blindness from Mutual Coupling in a Sunflower Phased Array

The most recent Aperture Array Verification System for the SKA-Low, AAVS3, has been designed with a regular sunflower head ‘Vogel’ layout with a 19 m radius. We use a fast Method-of-Moments solver to investigate the effects of mutual coupling of this style of regular layout in comparison to a more randomised layout. We show that this layout produces a blind spot at zenith at 125 MHz, where the embedded element pattern and station beam show a drop of around 5 dB. We then demonstrate that randomising the locations of the elements reduces the scale of this drop in beam, with greater randomisation producing greater reduction. We find that randomising each element position within an area of around 1.5 m radius is sufficient to eliminate this blind spot.