1、 Rec. ITU-R M.1644 1 RECOMMENDATION ITU-R M.1644 Technical and operational characteristics, and criteria for protecting the mission of radars in the radiolocation and radionavigation service operating in the frequency band 13.75-14 GHz (Question ITU-R 226/8) (2003) Summary This Recommendation provid
2、es the technical and operational characteristics, and criteria for protecting the radiolocation and radionavigation radars operating in the 13.75-14 GHz band. It contains a detailed description of the predominant shipborne radiolocation radar in the band, plus a tabular set of characteristics of all
3、 the known shipborne, airborne and ground-based radars operating in the band. The ITU Radiocommunication Assembly, considering a) that the antenna, signal propagation, target detection, and large necessary bandwidth characteristics of radars needed to achieve their functions are optimum in certain f
4、requency bands; b) that the technical characteristics and protection criteria of radiolocation and radionavigation radars are determined by the mission of the system and vary widely even within a band; c) that considerable radiolocation and radionavigation spectrum allocations (amounting to about 1
5、GHz) have been removed or downgraded since WARC-79; d) that some ITU-R technical groups are considering the potential for the introduction of new types of services (e.g. fixed satellite, wireless access, and high-density fixed and mobile) in bands between 420 MHz and 34 GHz used by radionavigation a
6、nd radiolocation radars; e) that representative technical and operational characteristics of radiolocation and radionavigation radars are required to determine the feasibility of introducing new types of systems into frequency bands in which the radars are operated; f) that criteria for protection o
7、f the radars missions are also needed for that same purpose; g) that some radiolocation and radionavigation radars operate in both the 13.75-14 GHz band and the 13.4-13.75 GHz band; h) that radiolocation and radionavigation radars operate in both airborne and shipborne platforms, by many administrat
8、ions in all regions of the globe, and on land by at least one administration, 2 Rec. ITU-R M.1644 recommends 1 that the technical and operational characteristics of the radars described in Annex 1 be considered representative of radars operating in the frequency band 13.75-14 GHz; 2 that the appropr
9、iate criteria for protecting the operational performance of those radars presented in Annex 1; 3 that those criteria be used in analysing compatibility between those radars and systems in other services; 4 that in the presence of any modulated continuous wawe (CW) interfering signals with most or al
10、l of its 3 dB emission bandwidth spanned by the radar receiver passband in the main beam direction, the ratio of interfering signal power to radar receiver noise power level, I/N, of 6 dB be used as the interference protection criteria for the radars described in Annex 1, consistent with the guidanc
11、e contained in Recommendation ITU-R M.1461. This protection criterion represents the net protection level if multiple interferers are present. This threshold value is to be used in conjunction with the overall mission-protection criteria presented in Annex 1. Annex 1 Characteristics of radiolocation
12、 and radionavigation radars and criteria for protection of their mission 1 Introduction The band 13.75-14 GHz is allocated on a primary basis to the radiolocation service, the FSS (Earth-to-space), and certain functions of the space research service. It is also allocated for the radionavigation serv
13、ice by some administrations. The standard frequency and time signal-satellite service (Earth-to-space) operates in this band on a secondary basis. 2 Mission The radars described in 2 through 5 of this Annex are used worldwide, primarily aboard ships operated by many administrations. They operate in
14、sea and coastal areas, and there are a few land-based sites. They are used to detect and track discrete approaching airborne and surface objects (conventionally referred to in radar literature as targets). Many ships are equipped with several of these radars, and radars of this type aboard one ship
15、cannot serve the needs of other ships even if they are nearby. Since some of the targets of interest are airborne at very low altitude, the 13.75-14 GHz band offers an ideal compromise between multipath phenomena and atmospheric attenuation for performance of this mission. Similarly, many airborne a
16、nd land-based radars perform the same function as the shipborne radar systems. Rec. ITU-R M.1644 3 3 Technical characteristics The radiolocation system characteristics contained herein represent the predominant type of shipborne radar operating in the 13.75-14 GHz band. Table 4 in Appendix 1 to this
17、 Annex provide characteristics for other airborne, shipborne, and land-based radar systems operating in the band 13.75-14 GHz. The characteristics in 2 through 5 of this Annex should be used in studies of sharing with these shipborne radars, and the characteristics in Appendix 1 should be used with
18、the other types of radars. 3.1.1 Transmitter power/radiated power The transmitter is a klystron with peak output power of 30 kW (45 dBW). Search loss from transmitter to antenna is 5 dB; track loss from transmitter to antenna is 4 dB. 3.1.2 Search Search peak equivalent isotropically radiated power
19、(dBW) = transmitter peak power (dBW) transmission line loss (dB) + antenna gain (dBi): Beam 1 peak e.i.r.p. = 45 5 + 31.5 = 71.5 dBW; Average e.i.r.p. = 57.2 to 54.9 dBW1; Beams 2, 3, and 4 peak e.i.r.p. = 45 5 + 28.5 = 68.5 dBW; Average e.i.r.p. = 54.2 to 51.9 dBW1. 3.1.2.1 Search waveforms The sea
20、rch system uses a coherent transmitter/receiver for digital moving target indicator processing. 3.1.2.1.1 Low pulse repetition frequency mode Pulse width (PW): 2.2 s phase coded with 0.2 s segments Pulse repetition interval (PRI): minimum = 60 s; maximum = 100 s Duty factor: maximum = 3.7% (14.3 dB)
21、; minimum = 2.2% (16.6 dB). 3.1.2.1.2 High pulse repetition frequency (clutter) mode Pulse width: 0.2 s Pulse repetition interval: between 10 and 14 s. 3.1.3 Track Track peak e.i.r.p. (dBW) = transmitter peak power (dBW) transmission line loss (dB) + antenna gain (dBi): Track peak e.i.r.p. = 45 4 +
22、38.5 = 79.5 dBW; Average acquisition e.i.r.p. = 62.5 to 61.0 dBW1; Average track e.i.r.p. = 59.5 to 58.0 dBW1. 1The average powers given here are for periods of time equal to a fraction of a second, and should not be compared to the e.i.r.p. limit in No. 5.502 of the Radio Regulations, which applies
23、 for a period of time equal to one second. 4 Rec. ITU-R M.1644 3.1.3.1 Track waveform The track system uses a coherent transmitter/receiver for pulse-Doppler processing. Pulse width: 0.2 s in acquisition; 0.1 s in track Pulse repetition interval: between 10 and 14 s Duty factor: acquisition 2% (17 d
24、B) to 1.4% (18.5 dB); track 1% (20 dB) to 0.7% (21.5 dB). 3.2 Radar receiver noise level and losses N = Radar receiver thermal noise = 134 dBW in a 10 MHz bandwidth. This is the noise level of the terrestrial environment in a 10 MHz reference bandwidth without any receiver-added noise. NF = Radar no
25、ise figure = 5 dB. Receiver noise level = 129 dBW (10 MHz bandwidth). This is the level with the receiver-added noise included. LRF= RF transmission line loss between the radar antenna and preamplifier = 2 dB. The overall receiving-system noise level referred to the antenna port and expressed in a 1
26、0 MHz reference bandwidth is therefore: 129 + 2 = 127 dBW 3.3 Antenna characteristics Each of these radars contains two separate antenna assemblies. One set of antennas is used for the search function, and another antenna is used for the acquisition and track functions. 3.3.1 Search antennas Configu
27、ration 1 elevation coverage is accomplished using one 10 antenna centred at 4.5 (1F) and one 20 antenna (4F) centred at 60, both facing forward, and two 20 antennas centred at 20 (2B) and 40 (3B), both facing backward. Figure 1 presents the composite elevation coverage pattern with all antennas supe
28、rimposed. Table 1 lists parameters of the search antennas. 1644-011F4F3B2BFIGURE 1Configuration 1 search main beam patternsRec. ITU-R M.1644 5 Azimuth rotation rate is 540/s. On ships with two systems, each radar covers 310 of azimuth. TABLE 1 Search antenna parameters Configuration 1 Configuration
29、2 elevation coverage is accomplished using two 2.5 antennas centred at 0 (1F and 2B) and two 10 antennas (3B and 4F) centred at 6.25 and 16.25 respectively. Figure 2 presents the composite elevation coverage pattern with all antennas superimposed. Table 2 lists parameters of the search antennas. Azi
30、muth rotation rate is 540/s. On ships with two systems, each radar covers 310 of azimuth. 1644-021F4F3B2BFIGURE 2Configuration 2 search main beam patternsTABLE 2 Search antenna parameters Configuration 2 Antenna position Elevation beamwidth (degrees) Elevation beam centre (degrees) Gain (dBi) Azimut
31、h beamwidth (degrees) 1F 2B 3B 4F 10 20 20 20 4.5 20 40 60 31.5 28.5 28.5 28.5 2.2 2.2 2.2 2.2 Antenna position Elevation beamwidth (degrees) Elevation beam centre (degrees) Gain (dBi) Azimuth beamwidth (degrees) 1F 2B 3B 4F 2.5 2.5 10 10 0 0 6.25 16.25 37.5 37.5 31.5 31.5 2.2 2.2 2.2 2.2 6 Rec. ITU
32、-R M.1644 TABLE 3 Radar antenna off-axis gain in azimuth 1644-0320 015 10 5 1052154020353025151050FIGURE 3Search radar antenna beam 1F gain patternsAzimuth off-axis angle (degrees)Gain(dBi)Configuration 2Configuration 1Off-axis angle (degrees) Configuration 1 gain (dBi) Configuration 2 gain (dBi) 18
33、0 0 0 10 0 9.5 2 8 4.5 8 14 3.3 23.7 29.7 3 24 30 2.5 26.9 32.9 1.5 29.2 35.2 1.1 31.2 37.2 0 31.5 37.5 1.1 31.2 37.2 1.5 29.2 35.2 2.5 26.9 32.9 3 24 30 3.3 23.7 29.7 4.5 8 14 9.5 3 8 10 0 0 180 0 Rec. ITU-R M.1644 7 3.3.2 Track antenna The track antenna is a monopulse four-horn fed parabolic dish
34、segment with elevation beamwidth of 1.2 and azimuth beamwidth of 2.4; gain is 38.5 dBi and side lobe levels are more than 20 dB below the main lobe. When designated to acquire a target, the antenna executes a limited size raster pattern and goes into track when the target is detected. 3.4 Planned ra
35、diolocation system modifications Radar detection of objects at low-elevation angles is being improved by increasing antenna gain on the horizon using existing search waveforms. Increased e.i.r.p. levels will be transmitted with the scan beam centred on the horizon as follows: Peak e.i.r.p. 2 elevati
36、on = 79 dBW: average e.i.r.p. = 59 dBW (track mode). The modified search antenna aperture is identical to the existing track antenna aperture. The modified search antenna is only used below 2 elevation. In todays system, the track antenna is the source of the maximum peak and average e.i.r.p. (79 dB
37、W and 59 dBW respectively). In the modified radar, the peak e.i.r.p. will remain at 79 dBW since the track and low-elevation search apertures will be the same, but the average e.i.r.p. below 2 (search) will increase due to the greater pulse widths used in search than in track. 4 Operational characte
38、ristics 4.1 System radiation time For deployed ships/systems, when the ships are in potentially hazardous areas, the systems must radiate continuously. 4.2 Radiolocation system geographic distribution Approximately 800 of these radars are in use. Insofar as interactions with geostationary satellites
39、 are concerned, it can be assumed that the radars are uniformly distributed on the Earths sea surface and that one-third of them are visible to a geostationary satellite. However, locally up to 70 of these radars could be operating within a 200 km2area and located from 1 km offshore to the radar hor
40、izon. The number of radars operating in the 13.75-14 GHz band is approximately 333. The probability, Pc, that a single FSS transmitter would operate co-frequency with a given radar operating in the 13.75-14 GHz band is approximately: Pc= BW / 250 where BW is the interferers bandwidth (MHz). The prob
41、ability that an interferers emission spectrum would overlap the passband of one or more radars aboard a cluster of ships can be much higher than that. 8 Rec. ITU-R M.1644 4.3 Range of radiolocation antenna heights The system mount deck height varies from 3 to 36 m above the waterline. The search ant
42、enna is approximately 5 m above the deck and the track antenna is approximately 4 m above the deck. 5 Criteria for protection of the radars mission 5.1 Surveillance requirements This radiolocation device is not a traditional surveillance type radiolocation device, but rather an integrated part of a
43、larger weapon system provided to protect a ship from incoming threats. Its use is driven by the threat environment. The demand for use is 100% when operating close to shorelines. 5.2 Interference threshold Recommendation ITU-R M.1461 Procedures for determining the potential for interference between
44、radars operating in the radiodetermination service and systems in other services, contains information on the interference threshold power level to be used in calculations of the potential for interference into radars. Interfering signals of the noise-like continuous-carrier type that is characteris
45、tic of all conventional communications services exert a virtually unalterable desensitizing effect on radiolocation radars, regardless of the radars waveform and signal processing. Consequently, the desensitization is predictably related to the intensity of the interference. In any azimuth sector in
46、 which such interference arrives, its power-spectral density simply adds to the power spectral density of the radar receiving system thermal noise, to within a reasonable approximation. If power spectral density of radar-receiver noise in the absence of interference is denoted by N0and that of noise
47、-like interference by I0, the resultant effective noise power spectral density becomes simply I0+ N0. An increase of I0+ N0, relative to N0, of about 1 dB would constitute significant degradation for the radiolocation service, even if it occurs only when the interference couples via the radar main b
48、eam. Such an increase corresponds to an (I + N )/N ratio of 1.26, or an I/N ratio of about 6 dB. This applies to the aggregate effect of multiple interferers, when present; the tolerable I/N ratio for an individual interferer depends on the number of simultaneous interferers and their geometry, and
49、needs to be assessed in the context of a given scenario. Because the 6 dB I/N ratio desensitization threshold applies when the strongest coupling condition occurs, including coupling via the radars main beam, as well as when coupling is weaker (as via radar-antenna side-lobes) it can be expressed for any particular radar as a pfd limit. If the antenna main beam capture area is 0.5 m2, the desensitization threshold for interference from commu-nications transmitters will then be 164 dB(W/(m2 4 kHz) for coupli
