1. Department of Physics, Box 8202, North Carolina State University, Raleigh, North Carolina 27695‐8202
2. Department of Electrical and Computer Engineering, Box 7911, North Carolina State University, Raleigh, North Carolina 27695‐7911
3. Electronic Technologies Division, MCNC, P. O. Box 12889, Research Triangle Park, North Carolina 27709‐2889