H. X. de Araujo, M. W. B. Silva, I. R. S. Casella, A. L. P. S. Campos, and C. E. Capovilla, “A C-Band Planar Metamaterial-Inspired Antenna Employing a Hexagonal Cell Periodic Structure”, Journal of Communication and Information Systems, vol. 33, no. 1, Mar. 2018.