1、 Rec. ITU-R M.1584 1 RECOMMENDATION ITU-R M.1584 Methodology for computation of separation distances between earth stations of the radionavigation-satellite service (Earth-to-space) and radars of the radiolocation service and the aeronautical radionavigation service in the frequency band 1 300-1 350
2、 MHz(Resolution 607 (WRC-2000) (2002) The ITU Radiocommunication Assembly, considering a) that the band 1 300-1 350 MHz is allocated on a primary basis to the aeronautical radionavigation service (ARNS) for use by ground-based radar systems; b) that the World Radiocommunication Conference (Istanbul,
3、 2000) (WRC-2000) has added a primary allocation to the radionavigation-satellite service (RNSS) (Earth-to-space) in the 1 300-1 350 MHz band; c) that WRC-2000 has raised the status of the radiolocation service from secondary to primary in the 1 300-1 350 MHz band; d) that the allocation to the radi
4、olocation service is used by terrestrial as well as airborne radar systems; e) that there is a potential for interference between uplink stations in the RNSS and radar systems of the ARNS and radiolocation service; f) that radar systems of the ARNS and radiolocation service can be protected with the
5、 implementation of adequate separation distances; g) that Appendix 7 of the Radio Regulations (RR) shall be used to determine the affected administrations for the coordination of specific RNSS earth stations in the Earth-to-space direction under RR No. 9.17, recognizing a) that WRC-2000 added RR No.
6、 5.337A stating the use of the band 1 300-1 350 MHz by earth stations in the RNSS and by stations in the radiolocation service shall not cause harmful interference to, nor constrain the operation and development of, the ARNS; b) that operational and practical difficulties exist in complying with and
7、 maintaining the separation distance between RNSS uplink stations and airborne radars, thus possibly adversely affecting the mission capabilities of the airborne radars; c) that, for the examples used in Annexes 1 and 2, in order for RNSS earth stations to properly protect ground and airborne radiod
8、etermination stations, it is necessary to provide an attenuation of 50 dB for elevation angles of 10 or less, noting a) that the application of the methodology for the example in Annex 1 results in computed separation distances ranging from 50-325 km between RNSS earth stations and radars in the rad
9、ionavigation service; 2 Rec. ITU-R M.1584 b) that the application of the methodology for the example in Annex 2 without a choke ring results in computed separation distances up to the radio horizon of the airborne radars, recommends 1 that the methodologies in Annexes 1 and 2 be taken into account,
10、when selecting the location of RNSS uplink earth stations in the range 1 300-1 350 MHz, in order to compute separation distance between RNSS uplink stations and radiolocation and aeronautical radionavigation radar systems; 2 that administrations continue to study the compatibility issues between RNS
11、S earth station transmitters and airborne radiolocation radars and provide these studies to ITU-R. NOTE 1 Administrations should continue to study the compatibility issues between RNSS satellite receivers and radars in the radionavigation and radiolocation services and provide these studies to ITU-R
12、. ANNEX 1 Methodology for computation of separation distances between earth stations of the RNSS (Earth-to-space) and terrestrial radars of the radiolocation service and the ARNS in the frequency band 1 300-1 350 MHz 1 Introduction New radionavigation-satellite systems will use the band 1 300-1 350
13、MHz for the transmission by uplink stations of information such as navigation, synchronization or integrity data, to a constellation of medium Earth orbiting (MEO) satellites. This study provides an analysis of the interference created by uplink stations into receiving terrestrial radar. It results
14、from the study that a separation distance permits to avoid excess interference into terrestrial radar. 2 Systems characteristics 2.1 Radiolocation and aeronautical radionavigation radars The radar parameters used in this Recommendation are those given in Recommendation ITU-R M.1463 Characteristics o
15、f and protection criteria for radars operating in the radiodetermination service in the frequency band 1 215-1 400 MHz, covering radars of the radiolocation service and ARNS. In order to calculate radar perturbation thresholds, the following formula and a 6 dB protection criteria (I/N) as given in R
16、ecommendation ITU-R M.1463 have been used: Pthreshold(dBm) = 10 log (K T0FB) + 24 Rec. ITU-R M.1584 3 TABLE 1 Radar-receiving parameters 2.2 Typical RNSS radio uplink stations Transmitted power: 57.1 dBm Antenna type: omnidirectional with a physical isolation for low elevation (typically 50 dB atten
17、uation with a choke-ring (see Appendix 2 to Annex 1 for the description of a choke ring) Orientation: zenith Maximum gain: 3 dBi Gain: 1 dBi for elevation angles less than 10 Modulation: spread spectrum (1.023 and 10.23 Mchip/s) Polarization: left-hand circular polarization Height: 2 m Network: less
18、 than 20 uplink stations regularly spaced around the world. Each uplink station transmits on the same frequency to a constellation of MEO satellites. The total power is used to transmit two signals, one spread with a 1.023 Mchip/s code and the other spread with a 10.23 Mchip/s code. While the 10.23
19、Mchip/s code signal has a power of 53 dBm, the 1.023 Mchip/s has a power of 55 dBm. As a worst-case illustration and for the purpose of this study, frequency of the uplink stations is taken as the same as the radar. However, the impact of a frequency shift is studied. 3 Interference of RNSS uplink s
20、tations into radar 3.1 Compatibility study In order to assess the separation distance necessary to protect radar reception, the propagation loss, L (dB), is calculated as: L = Pt+ Gt At FLt+ Gr FLr+ Rb Dpol Pthreshold= Pinterfering Pthreshold(1) Bandwidth (MHz) Reception antenna gain (dBi) Perturbat
21、ion threshold (dBm) System 1 0.780 33.5 119.1 System 2 0.690 38.9 119.6 System 3 4.4 and 6.4 38.2 108.8 and 107.2 System 4 1.2 32.5 115.7 Wind profile radars 2.5 33.5 114.5 4 Rec. ITU-R M.1584 where: Pt: transmitting interfering power (dBm) Gt: transmitting interfering gain (dBi) in the radar direct
22、ion At: physical isolation at low elevation (due to choke ring) (dB) FLt: transmitting feeder losses (dB) Pthreshold: perturbation threshold (dBm) Gr: reception gain (dBi) FLr: reception feeder losses (dB) Rb: rejection factor (dB) Dpol: polarization coupling factor (dB). The rejection factor Rbrepr
23、esents the amount of the RNSS emission total power which is filtered by the radar receiver. Thus, it takes into account the radar receiver bandwidth, the frequency offset between the radar and the RNSS uplink emission central frequencies and the RNSS signal normalized power spectral density (NPSD).
24、For a square binary phase-shift keying modulation (expected for RNSS): fcfcffNPSDRrTRrTRrRrRTrBffBffcffcfBfBfcfffcfBbdsindsind)(2/2/212/2/)(21)(0000000=+(2) where: Br: reception bandwidth. It is to be noticed that the slow code (code rate = 1.023 Mchip/s) is also a short code (1 023 chips). Conseque
25、ntly, the spectrum of the corresponding signal has 1 kHz line components. Some of these line components have a power level greater than the (sinc x)2values, but the average of lines keeps approximately a (sinc x)2shape. Taking into account that the reception bandwidth is large with respect to the 1
26、kHz intervals, a great number of line components are averaged and equation (2) is adequate to compute Rb. Following the determination of L, one can evaluate the corresponding separation distance. This is done through Recommendation ITU-R P.452 Prediction procedure for the evaluation of microwave int
27、erference between stations on the surface of the Earth at frequencies above about 0.7 GHz, as well as Recommendation ITU-R P.526 Propagation by diffraction. The method proposed in Recommendation ITU-R P.452, Table 5, has been used in order to derive the overall prediction taking into account the pat
28、h type (line-of-sight, line-of-sight with sub-path diffraction or trans-horizon). Rec. ITU-R M.1584 5 In Table 2 are given the main hypotheses that have been taken into account in the application of the above Recommendations: TABLE 2 Main hypotheses for protection distances calculations 3.2 Calculat
29、ion of separation distance beyond which protection is assured (protection distance) Equation (1) is applied for all radars given in Recommendation ITU-R M.1463, for both worst-case co-frequency operations and for 3 MHz frequency off-set operation between the centre frequency of the radar and the RNS
30、S emission. In Appendix 1 of this Annex are given the tables with the required loss calculations in order to protect each type of radar. Model Parameter Value Comment Tropospheric scatter Path centre sea-level refractivity: N0360 Compromise among all the continents worst values Ducting/layer reflect
31、ion Over-sea surface duct coupling corrections for the interfering and the interfered-with stations (Act, Acr) 0 dB It is assumed that the distance from each terminal to the coast along the great-circle interference-path is more than 5 km Terrain roughness parameter, that is the maximum height of th
32、e terrain above the smooth Earth surface (hm) 00= 10FIGURE 3Illustration of choke ringRadomeAbsorberCorrugatedwallRadius = R = N Wavelength = N compatible with far-field conditions12 Rec. ITU-R M.1584 ANNEX 2 Methodology for computation of separation distances between earth stations of the RNSS (Ear
33、th-to-space) and airborne radars of the radiolocation service in the frequency band 1 300-1 350 MHz 1 Introduction This Annex provides an analysis of the interference created by uplink stations into receiving airborne radars. 2 System characteristics 2.1 Airborne radiolocation radars The systems lis
34、ted in Table 3 are representative systems of airborne radars that are operational or planned for the 1 300-1 350 MHz band. 2.1.1 System A System A is an airborne, non-coherent, side-looking radar used for ocean surveillance. The radar will be carried on aircraft with an operation altitude of 15 500
35、to 25 500 ft (approximately 4.7-7.7 km) in over-water operations at ranges of 50 to 500 nm (approximately 92.6-926 km) from shore. 2.1.2 System B System B is a multichannel airborne radar measurement system with operations at altitudes not to exceed 10 000 ft (approximately 3 km). 2.1.3 System C Sys
36、tem C is an airborne radar that has two operator-electable, frequency-diverse pairs. The diverse frequencies have 15 MHz separation. In one mode, all four frequencies are used to eliminate second-time-around echoes. The radar is carried on a tethered balloon which is moored at an altitude of 10 000
37、to 15 000 ft (approximately 3-4.5 km). 2.1.4 System D System D is an airborne radar that is normally operated above 30 000 ft (approximately 9.1 km) (typically 30 000-40 000 ft, i.e. approximately 9.1-12.2 km). Rec. ITU-R M.1584 13 TABLE 3 Airborne radiolocation technical characteristics Parameter S
38、ystem A System B System C System D Frequency range (MHz) 1 300-1 350 1 215-1 350 1 215-1 400 1 215-1 400 Output power (kW) 15 19.2 8.4 27 Emission BW (MHz) 19 1 3 6, 12 Modulation Pulsed linear FM Linear FM spread spectrum Pulse w/linear FM chirp Pulse rate (pps) 55 250 369 300-1 000 Pulse width (s)
39、 28 50 260.4 5-50 Rise time 0.04 s 250 ns 0.1 s Fall time 0.04 s 20 ns 0.1 s Antenna gain (dBi) 20/22 27 35 33 Antenna heights (ft) 25 500 (approx. 7.7 km) 10 000 (approx. 3 km) 15 000 (approx. 4.7 km) 40 000 (approx. 12.2 km) Protection criteria (I/N) (dB) 6 6 6 Noise figure (dB) 4 4 3.87 5 Reflect
40、or size 4 2.5 and 2 9 (approx. 1.2 0.76 and 0.61 2.7 m) 4 4 (approx. 1.2 1.2 m)3 m Beam type Phased array Phased array Parabolic Pencil Beamwidth 39 (azimuth) or 12 (azimuth) 13 (elevation) 5.20 (azimuth) 10.45 (elevation) (1)3.5 Scan (2)(3)360 horizontal 360 azimuth 60 elevation Revolutions per min
41、ute Fixed 2 5 5 IF bandwidth (3 dB) (MHz) 14 9 20 (1)Horizontal first major side lobe 13.5 dBi at 2.7, vertical 3.5, 3 dB spoiled. (2)There are two possible antennas for this radar, both of which are mounted at a right angle to the flight track. The first antenna has a beamwidth, off boresight shape
42、 of 60 21 of azimuth with an elevation of 14 27 elevation off boresight. The second antenna has a beamwidth off boresight shape of 36 14 of azimuth with an elevation of 14 27 elevation off boresight. (3)The array is an active aperture capable of scanning 60 in the azimuth plane. Since the array, whe
43、n mounted on the aircraft, will not rotate, there will be a 240 region around the rear of the array which is naturally blanked at all times. The main beam can be pointed in any sector of a 120 region ( 60 from array boresight) in front of the array. 14 Rec. ITU-R M.1584 3 Interference of RNSS uplink
44、 stations into airborne radars Considering the airborne radar characteristics given in 2 of this Annex, we can derive the required loss (dB) in order to protect these airborne radars from RNSS uplink stations beacons. These required loss values have been obtained with equation (1) in 3.1 of Annex 1
45、and they are given in Appendix 1 to Annex 2. 3.1 Results Taking into account the maximum height (supposed to be amsl) of each kind of airborne radar, we have computed the required distance between the border of the area where the airborne radars are in operation, and the uplink RNSS stations using t
46、he free space loss propagation model (which is the worst case). For all the calculations we have assumed that the height (amsl) of the transmitting RNSS earth station is 1 000 m. TABLE 4 Free space separation distances (including choke ring on RNSS antenna) for airborne radar versus RNSS uplink stat
47、ion (zero frequency offset) If the choke ring attenuation of 50 dB is included in the computation, then the minimum separation required is 47 km (System A, 10.23 Mchip/s). The maximum required separation distance is 351 km (System D, addition of powers from both codes). If the choke ring attenuation
48、 is not included in the computation, then the minimum separation required is determined by the radio horizon of the airborne radar. 3.2 Conclusions From these examples, the methodology described herein, assuming an uplink gain of 1 dBi at elevation angles below 10 and the use of a choke ring providi
49、ng an additional attenuation of 50 dB, results in a separation protection distance of 349 km for the airborne radar (Radar D) having the worst-case parameters. For different parameters (radar receiving parameters, RNSS earth station transmitting parameters, absence of choke ring, etc.) other distances will be obtained. If the choke ring were not used in the example, the distances would become prohibitive for airborne radars. In additio
