The shape of the radio wavefront of extensive air showers as measured with LOFAR by Corstanje, A, Schellart, P, Nelles, A, Buitink, S, Enriquez, J, Falcke, H, Frieswijk, W, Horandel, JR, Krause, M, Rachen, J, Scholten, O, ter Veen, S, Thoudam, S, Trinh, T, van den Akker, M, Alexov, A, Anderson, J, Avruch, I, Bell, M, Bentum, M, Bernardi, G, Best, P, Bonafede, A, Breitling, F, Broderick, J, Bruegen, M, Butcher, H, Ciardi, B, de Gasperin, F, de Geus, E, de Vos, M, Duscha, S, Eisloeffel, J, Engels, D, Fallows, R, Ferrari, C, Garrett, M, Griessmseier, J, Gunst, A, Hamaker, J, Hoeft, M, Homeffer, A, Icobelli, M, Juette, E, Karastergiou, A, Kohler, J, Kondratiev, V, Kuniyoshi, M, Kuper, G, Maat, P, Mann, G, McFadden, R, McKay-Bukowski, D, Mevius, M, Munk, H, Norden, M, Orru, E, Paas, H, Pandey-Pommier, M, Pandey, V, Pizzo, R, Polatidis, A, Reich, W, Rottgering, H, Scaife, A, Schwarz, D, Smirnov, O, Stewart, A, Steinmetz, M, Swinbank, J, Tagger, M, Tang, Y, Tasse, C, Toribio, C, Vermeulen, R, Vocks, C, van Weeren, R, Wijnholds, S, Wucknitz, O, Yatawatta, S, Zarka, P