1. a Royal Signals and Radar Establishment, Malvern , Worcestershire , WR14 3PS , England
2. b Sandia Laboratories , Albuquerque , New Mexico , 87115 , U.S.A.
3. c Naval Research Laboratory , Washington D.C. , 20375 , U.S.A.
4. d Bell Laboratories , Murray Hill , New Jersey , 07974 , U.S.A.