Affiliation: | 1. D.I. and P.V.C. are at the Institute of Physics, PO Box 57, 11001 Belgrade, Yugoslavia;2. M.S. is in the Electrical Engineering Faculty of the University of Belgrade, Bul. Revolucije 73, 11000 Belgrade, Yugoslavia;3. I.P. is at the Istituto di Ricerca sulle Onde Electromagnetiche del CNR, Via Panciatichi 64, 50127 Florence, Italy |