[1] Univ Granada, Dept Appl Phys, E-18071 Granada, Spain
[2] Univ Valencia, Dept Appl Phys, E-46100 Valencia, Spain
[3] Univ Granada, Dept Electromagnetism & Mat Phys, E-18071 Granada, Spain
[4] Univ Granada, Higher Tech Sch Informat Technol & Telecommun Eng, E-18071 Granada, Spain
[5] Natl Univ Ireland Univ Coll Dublin, Sch Elect Elect & Mech Engn, Dublin 4, Ireland
[6] Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria