1、 Rec. ITU-R S.1528 1 RECOMMENDATION ITU-R S.1528 Satellite antenna radiation patterns for non-geostationary orbit satellite antennas operating in the fixed-satellite service below 30 GHz (Question ITU-R 231/4) (2001) The ITU Radiocommunication Assembly, considering a) that the use of space station a
2、ntennas with the best available radiation patterns will lead to the most efficient use of the radio-frequency spectrum; b) that both elliptical and circular beam antennas are used on operational space stations; c) that although improvements are being made in the design of space station antennas, fur
3、ther information is still required before a reference radiation pattern can be adopted for coordination purposes; d) that the adoption of a design objective radiation pattern for space station antennas will encourage the fabrication and use of orbit-efficient antennas; e) that it is only necessary t
4、o specify space-station antenna radiation characteristics in directions of potential interference for coordination purposes; f) that for wide applicability the mathematical expressions should be as simple as possible consistent with effective predictions; g) that nevertheless, the expressions should
5、 account for the characteristics of practical antenna systems and be adaptable to emerging technologies; h) that measurement difficulties lead to inaccuracies in the modelling of spacecraft antennas at large off-axis angles; j) that the size constraints of launch vehicles lead to limitations in the
6、D/ values of spacecraft antennas; k) that a multiple beam antenna on the non-geostationary-satellite orbit (non-GSO) has to provide an earth coverage field-of-view (FOV) of up to 30 half-cone angle from a medium earth orbit (MEO) satellite, and up to 60 from a low earth orbit (LEO) satellite; l) tha
7、t most non-GSO fixed-satellite service (FSS) satellites are planned to use a large number of beams per satellite with either steerable or fixed beams; m) that the peak gain of a multiple beam antenna decreases while the side-lobe level increases as a function of the off-axis beam pointing angle; n)
8、that the 1st and 2nd side lobes of a multiple beam antenna may be merged into the main beam when the beam is pointed toward or close to the edge of the Earth; o) that for a practical antenna, spill-over from the main reflector, subreflector, or diffraction from the supporting structure may significa
9、ntly affect the accuracy of our estimates in the near-in and far-out side lobe regions; 2 Rec. ITU-R S.1528 p) that actual radiation patterns of some kinds of multiple beam antennas may be significantly different from beam to beam, recommends 1 that for multiple-beam non-GSO satellite antennas in th
10、e FSS having either circular or elliptical beams, the following radiation patterns should be used as a design objective or to perform interference analysis: 1.1 measured antenna patterns Measured antenna patterns should be used in performing interference analysis whenever they are available. When a
11、measured pattern is not available, one or other of reference patterns given in the remaining sections may be used: 1.2 the reference pattern given by: G() = Gm 3 ( /b) dBi for 0 22.5Lens diameter, D / : 22.6 wavelength at 18.8 GHz Half power beamwidth, 2 b: 3.2 at 18.8 GHz, scanned 21 off-axis Gain
12、at 21 off-axis, Gm: 35 dBi MEO reference radiation pattern b= 1.6Gm= 35 Ls= 12 Y = 2 b= 3.2LF= 3 Z = 20.0G() = Gm 3 ( /b)2dBi for b Y = 35 3 ( /1.6)21.6 3.2G() = Gm+ Ls 25 log ( /Y ) dBi for Y Z = 23 25 log ( /3.2) 3.2 20.0= 35.6 25 log () G() = 3 dBi for 20.0 180LEO reference radiation pattern b= 1
13、.6Gm= 35 Ls= 6.75 Y = 1.5 b= 2.4 LF= 5 Z = 20.4 G() = Gm 3 ( /b)2dBi for b Y = 35 3 ( /1.6)2G() = Gm+ Ls 25 log ( /Y ) dBi for Y Z = 28.25 25 log ( /2.4) 2.4 20.4 = 37.76 25 log () G() = 5 dBi for 20.4 180 8 Rec. ITU-R S.1528 Using Recommendation ITU-R S.672 b= 1.6Gm= 35 Ls= 25 Y = 2.887 b= 4.62 LF=
14、 0 Z = 25.4 G() = Gm 3 ( /b)2dBi for b Y = 35 3 ( /1.6)21.6 4.62 G() = Gm+ LsdBi for Y 6.32 b= 10 4.62 10.1G() = Gm+ Ls+ 20 25 log ( /b) dBi for 6.32 b Z = 35.1 25 log 10.1 25.4 G() = 0 dBi for 25.4 180 ANNEX 2 Examples for recommends 1.4 The antenna pattern presented is applicable to a non-GSO sate
15、llite system at an altitude of 1 469 km, generating beams on the ground covering a 350 km radius cell (see Fig. 5). 1528-05AByx0SabFIGURE 5The study is performed at a frequency of 12 GHz. The three primary roots of the J1Bessel function are: 1= 1.2 2= 2.233 3= 3.238 Rec. ITU-R S.1528 9 In each case,
16、 the SLR considered is 20 dB and the number of secondary lobes is four. These two parameters give A = 0.95277 and = 1.1692. Lrand Ltare distances on the ground and depend on the beam roll-off (difference between the maximum gain and the gain at the edge of the illuminated beam). The calculation has
17、been performed using roll-off of 7 dB, 5 dB and 3 dB. The Lrand Ltinput parameters to be used are given in Table 2. TABLE 2*For a pointing angle 0of 0, relative to sub-satellite points (see Fig. 5) the results are plotted on the graph in Fig. 6. 1528-060 10203040506050403020100FIGURE 6Radiation cutt
18、ing of reference antenna diagram (degrees)Gainratio(dB)Roll-off = 3Roll-off = 5Roll-off = 7Roll-off 7 5 3 rLasin74.0asin64.0asin0.51tLbsin74.0bsin64.0bsin51.0* The coefficients depend on the side-lobe ratio chosen in this particular case, as well as on the roll-off at the edge of coverage. The Lrand Ltobtained are in metres. a: half-radial axis distance of the illuminated beam (degrees) (subtended at the satellite); b: half-transverse axis distance of the illuminated beam (degrees) (subtended at the satellite).
