Faculty of Electrical Engineering K.N. Toosi University of Technology Seyyed Khandan, Tehran, Iran.P.O. Box: 16315-1355Postal Code: 16317-14191Fax: +98 21 88462066Tel: +98 21 84062407, +98 912 1302238 E-mail: sadeghz@eetd.kntu.ac.irwebsite: http://wp.kntu.ac.ir/sadeghz