 earth station antenna and 1983 (see Section 26.4.6.2) and the spectrum/orbit allotment sidelobe gain levels (CCIR, 1990; Recommendation 580). For 26/16 Radio spectrum management example, the CCIR recommends for a new antenna, 5 metres in diameter, operating at 14GHz, that the maximum gain of at least 90% of the sidelobes in the directions of greatest concern should not exceed the values indicated in Figure 26.9 within the solid angle indicated in Figure 26.10. It is likely that corresponding targets will be set soon for satellite antenna beam overspill suppression. 26.6.4 National spectrum optimisation Two kinds of radio facility, which are needed nowadays in great quantity in some countries, are private fixed microwave links and vehicle borne radiotelephone systems of the land mobile service. Indeed, ensuring that such systems use spectrum efficiently, SO that the demand for frequency assignments can be met from finite bandwidth resources in parts of the spectrum where the radio pro- ANGLE OFF-AXIS (deg) pagation characteristics are suitable, may be the most difficult task that administrations face. However, cross frontier interference is not a major problem for these systems and it has not been considered Figure 26.9 Recommended design objectives for the appropriate for the ITU to draw up international regulations or sidelobe gain of large earth station antennas installed after guidelines for the management of the spectrum that they use. Each 1988. The maximum gain of 90% of the sidelobes within the solid angle shown in Figure 26.10 should not exceed administration, or group of administrations with a common policy 29 - 25 log dBi where Q is the off-axis angle in degrees in mobile radio, must find its own solutions. A third major area of work for administrations is co-ordinating the frequencies assigned to earth stations (typically of the fixed satellite service) and terrestrial stations (typically of the fixed service) in 26.6.4.2 Mobile radiotelephones shared frequency bands. These three problem areas are tou