1. Butlin, R.S., Parker, O., Walker, A.J. and Turner, J.A. (1976). Proc. 6th European Microwave Conf., Rome, Sept., p. 606
2. Houng, Y.M. and Pearson, G.L. (1978). J. Appl. Phys., 44, 3348
3. Crossley, I., Goodridge, LH., Cardwell, M.J. and Butlin, R.S. (1977). Inst, of Phys. Conf. Ser., 33b, 289
4. Tuck, B., Adegboyega, G.A., Jay, P.R. and Cardwell, M.J. (1979). Inst, of Phys. Conf. Ser., 45, 114
5. Higgins, J.A., Eisen, F., Welch, B., Robinson, G. and Hill, W. (1977). Inst, of Phys. Conf. Ser., 33b, 236