1、 Rec. ITU-R S.1512 1 RECOMMENDATION ITU-R S.1512 Measurement procedure for determining non-geostationary satellite orbit satellite equivalent isotropically radiated power and antenna discrimination (Questions ITU-R 231/4 and ITU-R 42/4) (2001) The ITU Radiocommunication Assembly, considering a) that
2、 some frequency bands are allocated for use by non-geostationary satellite orbit (non-GSO) satellite networks; b) that the number of operational and planned non-GSO satellite systems has risen significantly in the past ten years; c) that the interference experienced by such systems will become incre
3、asingly significant to other users sharing the frequency bands on a primary basis; d) that operators of non-GSO satellite networks and administrations may wish to measure certain non-GSO satellite radiofrequency (RF) characteristics; e) that the RF characteristics of non-GSO satellites are more diff
4、icult to measure than those of GSO satellites since the non-GSO satellites are moving with respect to the surface of the Earth, recommends 1 that the test procedure in Annex 1 may be used as a guide to determine the equivalent isotropically radiated power (e.i.r.p.) and antenna discrimination of non
5、-GSO satellites. Annexes 2 and 3 may be used as part of the measurement procedure to determine the maximum and minimum signal levels received by the test station. ANNEX 1 Measurement procedure for determining non-GSO satellite e.i.r.p. and antenna discrimination 1 Introduction The procedure which fo
6、llows is intended to provide guidance to administrations wanting to perform repeatable measurements of the downlink e.i.r.p. and transmit gain pattern of operational non-GSO satellite. 2 Equipment requirements The test method involves the use of an earth station with a large, fully steerable antenna
7、 which is capable of tracking a satellite, a spectrum analyser capable of making the necessary measurements and a computer upon which operates an automated test program which can make the measurements and record the data on a file. 2 Rec. ITU-R S.1512 3 Description of measurement test-set A block di
8、agram of the measurement test-set is shown in Fig. 1. Each of the parameters shown in Fig. 1 is defined in Table 1. 1512-01TSATLGLTALpLcAntenna tracking softwareTest equipment softwareComputerNoise figure: FSATracking control(Azimuth, elevationpositioning)Feed CableSpectrumanalyserLarge, fullysteera
9、bletest antennaFIGURE 1Measurement test-set block diagramRFinLNATest antenna: The test antenna should be fully steerable over as much of the horizon as possible. The antenna reflector should be as large as possible so as to have a larger receive gain which translates in a larger dynamic range in whi
10、ch to make measurements. However the antenna slew rate should allow the antenna to remain pointed at the non-GSO satellite as it moves across the sky. The low noise amplifier (LNA) should have as low a noise temperature as possible so as to minimize the test equipment noise floor. The cable connecti
11、ng the LNA to the spectrum analyser should be as short as possible and be of good quality so as to minimize the noise it adds to the test set-up. Spectrum analyser: A spectrum analyser is required that has the capability of being digitally controlled by a computer and of transferring measured data b
12、ack to the computer. A data bus connection between the computer and spectrum analyser is typically used for such applications. Next, the spectrum analyser should have a noise floor which is lower than the equipment noise Rec. ITU-R S.1512 3 floor, otherwise the spectrum analyser noise floor will lim
13、it the dynamic range over which measurements can be taken. This can be calculated analytically by determining the temperature of the set-up (Annex 3) and comparing it to that of the analyser. An alternate method to the analytical calculation is to attenuate the signal into the spectrum analyser by 1
14、0 dB and verifying that the (I + N)/N has changed by less than 1 dB. Computer system: The computer system serves two functions. First it must steer the antenna towards the non-GSO satellite and second it must collect the necessary data. To accomplish the first function requires orbital data of the n
15、on-GSO satellite (apogee altitude, perigee altitude, inclination, argument of perigee, and time of ascending node) being studied in order to predict where and when it will appear on the horizon. The satellite can then be tracked by predicting its location over time or by using a closed loop tracking
16、 system, which is part of the antenna subsystem. The second function of the computer is to take measurements at regular time intervals and record the measurement on a computer file along with other positional data such as the azimuth and elevation of the test antenna. TABLE 1 Fixed parameters requir
17、ed for non-GSO satellite characterization tests Parameter description Symbol Units Value Nominal non-GSO satellite parameters Transmit power into antenna PSdBW Altitude of satellite hskm Occupied bandwidth of downlink when modulated BSocMHze.i.r.p.s Ls(if constant) e.i.r.p.s LsdB Difference (e.i.r.p
18、.s Ls) (variable)(1)Dif. (e.i.r.p.s Ls) dB Downlink frequency fDGHz Reference bandwidth BrefHz Test antenna coordinates Latitude ftestdd:mm:ss.s Longitude ltestddd:mm:ss.s Antenna height (amsl) htestm Test antenna characteristics Diameter Dtestm Receive gain (at fD) GRX testdBi Noise temperature TA
19、testK 4 Rec. ITU-R S.1512 TABLE 1 (end) 4 Conduct of the measurement test Maximum power calculation: The first step in preparing the equipment is to ensure that the set-up is not overloaded by the maximum received power in the entire bandwidth of the LNA. By adjusting gains or adding attenuation alo
20、ng the receive path, it is possible to ensure that the spectrum analyser is not over driven. The expression below can be used to calculate the received signal level of the test-carrier being measured at the input to the spectrum analyser. settesttestRXabsssstestRXGGLLGPP+Gf7Gf8Gf6Ge7Ge8Ge6+= (1) whe
21、re: PRX test: power of the received signal at the spectrum analyser (dBW) Ps: power at the flange of the satellite antenna (dBW) Gs: gain of the satellite antenna in the direction of the test station (dBi) Ls: free space loss which is calculated using the equation: dB4log102Gf7Gf7Gf8Gf6Ge7Ge7Ge8Ge6=
22、dLsParameter description Symbol Units Value Test-set parameters Antenna feed loss LFdB Gain of LNA GLdB LNA noise temperature TLK Cable loss LcdB Spectrum analyser data Make and model number Spectrum analyser settings during measurements Input attenuation dB Reference level dBm Amplitude resolution
23、dB/Div Centre frequency FCGHz Frequency span SPAN kHz Resolution bandwidth ResBW kHz Video bandwidth VBW kHz Normalized noise-floor(2)NoSAdBm (1) In the case where sticky beams or an isoflux antenna is not used on the non-GSO satellite, the difference between the maximum on-axis e.i.r.p. Lsand the m
24、inimum edge-of-beam e.i.r.p. Lsfor the intended service area should be given. (2)Displayed noise-floor is that which is determined after application of correction factors for log amplifier, envelope detector and resolution-to-normalized bandwidth. Rec. ITU-R S.1512 5 where: d : distance from test an
25、tenna to satellite (m) : wavelength of the signal (m) Labs: atmospheric absorption (dB) GRX test: gain of the test antenna including feed loss (measured at the output flange) (dBi) Gtest-set: gain of the test-set is calculated using the equation: cLsettestLGG =(2)where: GL: gain of the LNA (dB) Lc:
26、loss of the cable (dB). An example calculation of the maximum received power is given in Annex 2. Minimum power calculation: The noise floor of the spectrum analyser and the test-set needs to be established to determine the dynamic range over which measurements can be made. The method for determinin
27、g the practical minimum signal power that can be measured by the test set is explained in Annex 3. e.i.r.p. calibration: The next step consists of calibrating the test set-up. Establishing the e.i.r.p. of the non-GSO satellite is most accurately done by measuring the energy level of a source with a
28、known e.i.r.p. The measured level then serves as a reference power flux-density (pfd) which can be used to determine the e.i.r.p. of the non-GSO satellite. Various stable RF sources can be used as a calibration reference such as a GSO satellite beacon that is transmitted at a known e.i.r.p. or certa
29、in radio stars. If the equipment is not calibrated in this way, the measurements which are made will give information as to the relative gain of the non-GSO satellite in various directions but will not allow the exact power radiated in a given direction to be determined. As part of the calibration p
30、rocess, it is important to measure the variation in receive gain of the test set across the frequency band which will be used for the tests. Since variations of 2 to 3 dB across the measurement band are not uncommon, it is important to know the extent of the gain variation between the frequency used
31、 to measure the reference e.i.r.p. level and the frequency at which the measurement will be taken. Measurement of the non-GSO satellite signal: On each pass of a given non-GSO satellite, the tracking antenna follows the satellite and measurements are made of energy emanating from the satellite. At e
32、ach measurement point, the azimuth and elevation of the antenna need to be recorded for later processing. Prior to each new measurement, the software will instruct the spectrum analyser to clear the trace. An average over three sweeps of the frequency span should be executed to minimize the effect o
33、f any short-term fluctuation in transmitted power level. The time between data samples needs to be sufficiently short so as to capture the shape of the satellite antenna side lobes. The complexity of the non-GSO satellite transmit beam pattern and the altitude of the satellite are the two variables
34、which will need to be considered when establishing the required time increment between measurements. The minimum set-up time required by the test-set 6 Rec. ITU-R S.1512 is determined by the time required by the spectrum analyser to complete the three sweeps, make the measurement, pass the informati
35、on to the computer and for the computer to store the information. The spectrum analyser minimum sweep time is a function of the span and resolution bandwidth and is available from the manufacturers specifications. When the non-GSO satellite passes through a zone close to the GSO arc, it will be nece
36、ssary to take into account the potential interference contribution from GSO satellites. This may limit the amount of data that can be collected as the test antenna passes through a narrow region surrounding the GSO arc. An initial survey of the GSO arc prior to the commencement of tests may prove us
37、eful in finding a narrow, unused band over a significant portion of the GSO arc in which a continuous wave (CW) test carrier may be used. Tests should be performed under clear-sky conditions to minimize the variation in measured signal levels in the course of a test. Preferably the test site locatio
38、n should have a horizon as close to a 0 elevation angle in all directions to allow the largest field of view possible. If the non-GSO satellite travels on a repeating ground track, there will only be a finite set of measurement cuts of the antenna pattern. Testing from additional sites may be requir
39、ed in order to obtain sufficient data to characterize the non-GSO satellites transmit e.i.r.p. pattern. 5 Processing of data collected Non-GSO satellite with time invariant e.i.r.p. patterns: If the non-GSO satellite has an e.i.r.p. pattern that does not change with respect to the sub-satellite poin
40、t then each pass by the test site constitutes a cut of the antenna pattern. With enough cuts it is possible to construct a plot of the satellites e.i.r.p. with regards to its pitch and roll angle from nadir. In order to obtain such a plot from the collected data, the orbital parameters of the non-GS
41、O satellite along with the azimuth and elevation of the test antenna at each data point will be needed to determine: d : distance to the non-GSO satellite from the test station 1:pitch angle of the test station with regards to the nadir of the satellite 2:roll angle of the test station with regards
42、to the nadir of the satellite. The following equation can be used to find the e.i.r.p. of the non-GSO satellite (e.i.r.p.s) in the direction (1, 2): callevelddpriepriemesrefrefs+GfaGfaGfbGf9GeaGeaGebGe9+= log20 (3) where: e.i.r.p.ref: e.i.r.p. of the reference source (dBW) dref: distance from the ea
43、rth station to the reference source (m) dmes: distance from the earth station to the satellite under measurement (m) level : measured difference of the power between the level of the reference source and the non-GSO satellite (dB) cal : gain variation between reference frequency and measured frequen
44、cy (dB). Rec. ITU-R S.1512 7 Once all the data points have been converted to e.i.r.p.s, 1, and 2a plot can be made of e.i.r.p.sversus 1and 2. Software which draws contour levels on three dimensional data can be used to simplify the presentation of the information. Comparing these plots for the diffe
45、rent satellites in the constellation will demonstrate if individual satellites are operating outside of their specified envelope. Non-GSO satellite with time varying e.i.r.p. pattern: In cases where the non-GSO satellite e.i.r.p. pattern varies in time, it is not possible to measure an e.i.r.p. patt
46、ern. An example of such a type of pattern are sticky beams, where the boresight of the non-GSO satellite beam stays pointing at a given geographic location while that location is visible. As with a GSO satellite, the test station observing a non-GSO satellite with a sticky beam would always see the
47、same point in the non-GSO satellite beam. For non-GSO satellites with time varying e.i.r.p. patterns, the most that can be deduced is the equivalent pfd (epfd) at the test site for either one satellite or for the entire constellation if the non-GSO satellite is on a repeating ground track (see Note
48、1). This is accomplished by first finding the pfd at the test site for each data point by using the equation: callevelGLLprierefsrefabsref+=2m1 (4) where: : pfd at the site due to the non-GSO satellite in the reference bandwidth (Bref) of the spectrum analyser (dB(W/(m2 Bref) e.i.r.p.ref: e.i.r.p. o
49、f the reference source (dBW) Labs-ref: atmospheric loss in the direction of the reference source (dB) Ls-ref: free space loss in the direction of the reference source (dB) :2m1G gain of a 1 m2antenna (dBi) cal : gain variation between reference frequency and measured frequency (dB). Once the pfd, azimuth and elevation with respect to test antenna location are known, the off-axis mask of an antenna pointing towards a GSO satellite can be added to the data to get the epfd from a specific non-GSO satellite. By using all the data points gathered,
