1. Optoelectronic Division, Engineering Department, University of Sannio, Corso Garibaldi 107, 82100 Benevento, Italy
2. Department for Technologies, University of Naples Parthenope, Centro Direzionale, Isola C4, 80143 Napoli, Italy
3. Electromagnetism and Telecommunication Unit, Faculty of Engineering Mons, 7000 Mons, Belgium