Kopilovich, L.E.: 'On perfect binary arrays', Electronics Letters, 1988, 24, (9), p. 566-567, DOI: 10.1049/el:19880385
IET Digital Library, https://digital-library.theiet.org/;jsessionid=76q3nn8zszbl.x-iet-live-01content/journals/10.1049/el_19880385