ed for terrestrial point-to-point and satellite communications and radar. Wi-Fi and WiMAX use some frequency bands within this range. Millimetric: 30 to 100 GHz This range is unaffected by ionospheric conditions but has moderate to severe attenuation due to atmospheric conditions. It is used for limited line-of-sight communications, typically 10 km. There is limited usage for this range-mainly short-distance speech and data links, but increasing usage is likely, especially for indoor applications. References Braun, G. (1986) Planning and Engineering of Short-Wave Links, Second Edition, John Wiley & Sons. Cannon, P. S. (1987) The Evolution of Meteor Burst Communications Systems, J. IERE. 57(3). Damboldt, T. (1975) A Comparison between Deutsche Bundespost Ionospheric HF Propagation Predictions and Measured Field Strengths, Proceedings NATO AGARD, Radio Systems and The Ionosphere Conf. 173(May). Dick, M. I. (1990) Propagation Model of CCIR Report 894, Appleton Laboratories. Hitney, H. V. (1990) IONOPROP, Ionospheric Propagation Assessment Software and Documentation, Artech House. Maslin, N. M. (1987) H.F. Communications: A Systems Approach, Pitman. Millington, G. (1949) Ground Wave Propagation over Inhomogeneous Smooth Earth, Proceedings IRE 96:53-64. Resources Boithias, L. (1987) Radio Wave Propagation, North Oxford Academic Publishers. Budden, K. G. (1985) The Propagation of Radio Waves, Cambridge University Press. Friis, H. T. (1946) A Note on a Simple Transmission Formula, IRE Proc. (May) 254-256. Johnson, R. C., and Jasick, H. (eds.) (1984) Antenna Engineering Handbook, McGraw-Hill. Picquenard, A. (1984) Radio Wave Propagation, Philips Technical Library, McMillan Technical Press. Stanniforth, J. A. (1972) Microwave Transmission, English University Press. Stark, A. (1986) Propagation of Electromagnetic Waves, Rohde & Schwarz. 9 Antennas Martin Smith Nortel Ltd. Types of Antenna Antennas form the link between the guided parts and the free-space parts of a communica- tions system. The purpose of a transmitting ant