The biggest 20m array I've heard of was an aurora activity measurement site in Sweden that was built of 16 Versatowers with a TH6DXX on each. The array was steerable +/- 15 degrees from north using a phasing network. The mainlobe was 6 deegrees wide (-6dB) according to one of the scientists, Ake/SM5API. 73 de Ingo, SM5AJV / 8S5A