inter governmental undertakings to respect the rights of foreign possible to reduce such interference to an acceptable level by stations to use specified frequency assignments. increasing the orbital separation between the satellites, but this A frequency assignment planning conference may also be a help- option is of declining value as the number of satellites in use ful forum at which an administration with an immediate require- increases. In order to ensure that full use can be made of the ment for a new assignment in a crowded frequency band can medium, these entries of interference must be reduced by using negotiate adjustments to established assignments which will make earth station and satellite antennas with low sidelobe gain and by way for the new station. designing satellite networks to minimise the spectral power density Frequency assignment or frequency allotment planning may also of sidelobe radiation. be used to reserve a share of a frequency band, associated in the case The CCIR recommends limits on the spectral power density of satellite services with an arc of the geostationary satellite orbit, radiated off beam by transmitting earth stations. For example, at for the exclusive use of specified, and typically every, country. Such 6GHz the e.i.r.p. due to a wide band emission radiated at Q degrees a plan is sometimes drawn up for a frequency band which is not yet off axis should not exceed (35 - 25 log Q) dBW in any sampling in general use, in case a country, at some time in the future, should bandwidth of 4kHz when Q lies between 2.5° and 48°. The corre- find it impossible to get access to the band for a new system, because sponding limit for off axis angles greater than 48° is minus 7dBW the whole band has by that time become filled by the systems of per 4kHz. More stringent limits apply to antennas installed since other countries. Recent examples of such planning are the frequency 1988. assignment plans for satellite broadcasting that were agreed in 1977 Also, design objectives have been set for