Carlos Crespo-Cadenas, PhD, is a Full Professor at the Universidad de Sevilla, Spain. María José Madero-Ayora, PhD, is an Associate Professor at the Universidad de Sevilla, Spain. Juan A. Becerra, PhD, is an Associate Professor at the Universidad de Sevilla, Spain. The authors are members of IEEE and the Microwave Theory and Techniques (MTT) Society and have published over 70 papers and served as reviewers for several research journals and international conferences.