Manuscript received February 17;
1997. This work was supported by the office of Naval Research. K. Goverdhanam and L. P. B. Katehi are with the Radiation Laboratory;
University of Michigan;
Ann Arbor;
MI 48109 USA. R. N. Simons is with the NASA Lewis Research Center NYMA Group;
Cleveland;
OH 44135 USA. Publisher Item Identifier S 1051-8207(97)05424-X;