1、QUESTION ITU-R 42-1/4 Characteristics of antennas at earth stations in the fixed-satellite service (1990-1993) The ITU Radiocommunication Assembly, considering a) that the radiation fields close to antennas will affect the level of coupling between earth-station antennas in the fixed-satellite servi
2、ce (FSS) and nearby antennas using the same frequency bands; b) that the radiation fields of antennas may also be affected by the use of pit shielding; c) that earth-station antennas with more than one beam are feasible, and that the use of such antennas may be preferable to employing several single
3、-beam antennas at an earth station; d) that frequency re-use might be achieved with orthogonally polarized signals; e) that the precision of satellite station-keeping and attitude control may improve as a result of the development of more advanced control techniques in the satellite sub-systems; f)
4、that at higher frequency bands (i.e. 20-30 GHz) phased array antennas are also likely to be used, decides that the following Question should be studied 1 What is the relationship between near and far field patterns of earth stations in the FSS and other stations using the same frequency bands? 2 Wha
5、t is the coupling between antennas close to one another? 3 What is the effectiveness of pits or other devices for providing shieldings? 4 What are the radiation characteristics of each beam of multi-beam antennas? 5 What are the limitations on the number of beams that can be generated by a single an
6、tenna, and what is the minimum achievable angular separation between the beams? 6 What is the polarization discrimination performance of antenna systems in all angular regions with particular regard to the antenna type? 7 What are the desirable limits of steerability of earth-station antennas for geostationary satellites? 8 What are the radiation characteristics of phased array antennas? further decides 1 that the results of these studies should lead to the formulation of appropriate Recommendations by 2006. NOTE 1 See Recommendation ITU-R S.736.
