C. H. Huang (Department of Electrical Eng., National Dong Hwa Univ., 1, Sec. 2, Da Hsueh Road, Hualien, 974301, Taiwan )

S. W. Tan and W. S. Lour (Department of Electrical Eng., National Taiwan Ocean Univ., 2 Peining Road, Keelung, 20224, Taiwan )

E-mail:tanshwei@mail.ntou.edu.tw

H. Lo and C. Lo (Graduate Institute of Electrical Eng., National Taiwan Univ., 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan )