y Feed vitably approximate which means that much HF antenna design is Antennas. In The Handbook of Antenna Design, (eds. A.W. empirical. Rudge et al), Peter Peregrinus (IEE), London. Most HF antennas are based on dipoles, monopoles or wire Ludwig, A.G. (1973) The Definition of Cross- Polarisation, IEEE antennas, Complementary elements such as loops or slot antennas Trans., AP-211 (1), 116. are also used. Directionality or gain is achieved by arrays of ele- Milligan, T. (1985) Modern Antenna Design, McGraw-Hill, New ments. A prime requirement of most HF antennas is that they are York. broadband in order that the optimum propagation frequency can be Mittra, R. (1975) Numerical and Asymptotic Methods in Electro- used. The radiation patterns of the basic elements are wide band but magnetics, Springer Verlag, Berlin. the input impedance or VSWR is narrow band. To overcome this Olver, A.D. (1986) Basic Properties of Antennas. In The Handbook limitation a tuning unit has to be incorporated into the system. The of Antenna Design (eds. A.W. Rudge, et al) Peter Peregrinus wide band operation is achieved with automatic tuning units. (IEE), Chapter 1. Pratt, T. and Bostian, C.W. (1986) Satellite Communications, Wiley, New York. 17.6 References Rahmat-Samii, Y. (1986) Reflector Antennas. In Antenna Handbook (eds. Y.T. Lo and S.W. Lee) Van Nostrand, New York. Chapter Balanis, C.A. (1982) Antenna Theory: Analysis and Design Harper & Row, New York. Rudge, A.W., Milne, K. Olver, A.D. and Knight, P. (Eds.) (1986) Bennett, S.B. and Braverman, D.J. (1984) INTELSAT VI - A Con- The Handbook of Antenna Design, Peter Peregrinus (IEE), Lon- tinuing Evolution Proc. IEEE, 72, 1457. Rusch, W.V.T. and Potter, P.D. (1970) Analysis of Reflector An- Bergman, J., Brown, R.C., Clarricoats, P.J.B. and Zhou, H. (1988) tennas, Academic Press, New York. Sythesis of Shaped Beam Reflector Antenna Patterns, Proc. Rusch, W.V.T., Ludwig, A.C. and Wong, W.G. (1986) Analytical IEE, 135 (H), (1) 48. Techniques for Quasi-Optical Antennas. In The Handbook of B