Ferran Martín, IEEE Fellow, is a Full Professor of Electronics at Universitat Autònoma de Barcelona (UAB), Spain. Lei Zhu, IEEE Fellow, is a Full Professor in the Faculty of Science and Technology at the University of Macau, Macau SAR, China. Jiasheng Hong, IEEE Fellow, is a Full Professor in the Department of Electrical, Electronic and Computer Engineering at Heriot-Watt University, Edinburgh, UK. Francisco Medina, IEEE Fellow, is a Full Professor of Electromagnetism at Universidad de Sevilla, Seville, Spain