1、 Rec. ITU-R M.1640 1 RECOMMENDATION ITU-R M.1640 Characteristics of, and protection criteria for sharing studies for radars operating in the radiodetermination service in the frequency band 33.4-36 GHz (Questions ITU-R 213/7 and ITU-R 226/8) (2003) Summary This Recommendation provides the technical
2、characteristics and protection criteria for the radiodetermination systems operating in the band 33.4-36 GHz. The text was developed as a resource document intended to support sharing studies where sharing between the radiodetermination service and other services may be possible. The ITU Radiocommun
3、ication Assembly, considering a) the antenna, signal propagation, target detection, and large necessary bandwidth characteristics of radar to achieve their functions are optimum in certain frequency bands; b) that the technical characteristics of radiodetermination radars are determined by the missi
4、on of the system and vary widely even within a band; c) that considerable radiolocation and radionavigation spectrum allocations (amounting to about 1 GHz) have been removed or downgraded since WARC-79; d) that representative technical and operational characteristics of radars are required to determ
5、ine the feasibility of introducing new types of systems into frequency bands; e) that procedures and methodologies to analyse compatibility between radars and systems in other services are provided in Recommendation ITU-R M.1461; f) that radiodetermination radars operate in the band 33.4-36 GHz; g)
6、that the frequency band 33.4-34.2 GHz is allocated to the radiolocation service on a primary basis; h) that the frequency band 34.2-34.7 GHz is allocated to the radiolocation and space research (deep space) (Earth-to-space) services on a primary basis; j) that the frequency band 34.7-35.2 GHz is all
7、ocated to the radiolocation service on a primary basis and to space research service on a secondary basis; k) that the frequency band 35.2-35.5 GHz is allocated to the meteorological aids and radiolocation services on a primary basis; l) that the frequency band 35.5-36 GHz is allocated to the meteor
8、ological aids, Earth exploration-satellite (active), radiolocation, and space research (active) services on a primary basis, 2 Rec. ITU-R M.1640 recommends 1 that the technical and operational characteristics of the radiodetermination radars described in Annex 1 be considered representative of those
9、 operating in the frequency band 33.4-36 GHz; 2 that in the case of continuous (non-pulsed) interference, an interfering signal power to radar receiver noise power level, I/N, of 6 dB should be used as the required protection level for radiolocation systems for sharing studies in general; 3 that for
10、 studies of sharing the band 33.4-36 GHz between radars in the radiodetermination service and systems in other services, the following criteria be used: that for radiometric imagers the short-term protection criteria should be 137.8 dB(W/2 GHz) for not longer than 3 s, and the long-term protection c
11、riteria should be no more than 144.8 dB(W/2 GHz) for not longer than 60 s; that for metric radars and seekers the short-term protection criteria should be 126.2 dB(W/6 MHz) for not longer than 5 s, and the long-term protection criteria should be no more than 136.1 dB(W/6 MHz) for not longer than 60
12、s. Annex 1 Characteristics of, and protection criteria for radars operating in the radiodetermination service in the frequency band 33.4-36 GHz 1 Purpose The characteristics and protection criteria in this Recommendation have been provided for use in sharing studies called for under Resolutions 712
13、(WRC-2000) and 730 (WRC-2000) and to assess the compatibility between the radars and other systems operating in the band 33.4-36 GHz. 2 Background WRC-97 was asked to consider the provision of up to 1 GHz of frequency spectrum around 35 GHz for use by space-based active earth sensors. ITU-R studied
14、the compatibility between active spaceborne sensors and systems in the radionavigation and radiolocation services (multiple bands were considered). While studies performed prior to WRC-97 indicated that it is possible to allow active spaceborne sensors and the radar systems to co-exist in the same b
15、and without exceeding the protection criteria, WRC-97 decided to allocate 35.5-36 GHz to the SRS on a primary basis subject to No. 5.551A of the Radio Regulations (RR). WRC-2000 resolved to review this allocation, amongst others in the 35-38 GHz band, and established WRC-03 agenda item 1.12 to revie
16、w this issue. This Recommendation provides the technical characteristics and protection criteria for the radiolocation systems operating in the frequency band 33.4-36 GHz. Rec. ITU-R M.1640 3 3 Technical characteristics Frequencies around 35 GHz and 94 GHz, correspond roughly to the first two propag
17、ation windows in the atmospheric absorption characteristics of the millimeter wave spectrum, and use of these frequencies is required by systems in the radiodetermination service in order to achieve the high measurement accuracy and target resolution possible at millimeter wavelength. Both passive a
18、nd active sensors operating in the radiodetermination service around these frequencies are used for mapping, target identification, navigation, aim-point determination, test range instrumentation, etc. Table 1 summarizes technical characteristics of representative systems deployed in these bands. Th
19、is information is sufficient for general calculation to assess the compatibility between these radars and other systems. TABLE 1 Technical characteristics of radars around 35 GHz 4 Protection criteria Short-term interference criteria are developed in the following paragraphs for the terrestrial radi
20、olocation systems given in Table 1. Parameter Imaging Imaging Metric Metric Seeker Sensor type Passive Active Active Active Active Modulation Pulse Pulse Pulse Linear FM Compression ratio 200 Pulse width 0.05 0.25 0.05 10 Tx peak power (kW) 0.5 135 1 0.001 PRF (kHz) 30 1 50 10 RF bandwidth (MHz) 80
21、10 101 12 Antenna gain (dBi) 35 30 52 51 28.7 Beamwidth (degrees) 0.5 3.0 0.75 10 0.25 0.25 0.5 0.5 4.4 4.4 Rx IF bandwidth (GHz) 2 0.040 0.006 0.185 0.100 Noise temperature (K) 850 Noise figure (dB) 4.5 10 10 5 Rx sensitivity (dBm) 81 95 78 93 Tuning Fixed Fixed Fixed Frequency hop Fixed PRF: pulse
22、 repetition frequency 4 Rec. ITU-R M.1640 4.1 Radiometric imagers Assuming negligible system gain variation, the minimum temperature sensitivity, T of a radiometric imaging system is: irAtBTTT+= (1) where: TA: antenna noise temperature Tr: receiver noise temperature B: RF bandwidth ti: integration t
23、ime. The radiometer threshold, P is given by: P = k T B (2) where k is Boltzmans constant = 1.38 1023, and T and B are as given above. Using equations (1) and (2), we find that a radiometer with a 2 GHz bandwidth, 850 K system noise temperature and a 1 ms integration time has P = 137.8 dB(W/2 GHz).
24、Short-term protection criterion Given that it is an unlikely event, an operator can accept a severely degraded image for several seconds. Permitting the unwanted signal level to approach the radiometers threshold results in an allowed unwanted signal level of 137.8 dB(W/2 GHz) for no more than 3 s.
25、Long-term protection criterion A lesser degradation may be considered for time periods lasting up to 1 min. In this case the degradation is not necessarily readily evident to an operator, but does cause some loss in image resolution. Permitting the unwanted signal to reach 20% of the radiometers thr
26、eshold yields an allowed interference level of 144.8 dB(W/2 GHz) for no more than 60 s. 4.2 Metric radars and seekers For the case of terrestrial metric (instrumentation) radars and the seekers, we note that two important performance parameters, angular accuracy and target detection range R, are rel
27、ated to the received S/N by: NS/1(3) R 4/1NS(4) Narrow antenna beamwidth and high angular accuracy are possible with fairly small antenna sizes at millimeter wavelengths. This characteristic, in fact, is a major reason why missile seekers and instrumentation radars have been developed at these frequ
28、encies. From equations (3) and (4) we see Rec. ITU-R M.1640 5 that the angular accuracy of the radar is more sensitive to the received S/N than is the detection range so this performance parameter will be used to determine allowed interference levels1. As in the case of the imaging system in the pre
29、vious section, we can establish short term and long-term criteria for allowed degradation in system performance due to unwanted signals (interference). Short-term interference is allowed to significantly degrade the system for a period of time short enough that it may be acceptable to the operator,
30、given that it is an unlikely event. Long-term interference is allowed to incrementally degrade system performance to an extent not readily apparent to the operator, but is otherwise acceptable for the specified duration of time. Short-term protection criterion A degradation in the radar S/N will cau
31、se a tracking error, which can partially negate the advantage of operating at higher frequencies, and may significantly affect the radars mission. Permitting an unwanted signal to reach the radar noise level (I/N = 0 dB) will result in a 40% increase in the angle error. We can again assume that this
32、 degradation is not overly important given that it is an unlikely event for periods of time less than about 5 s. The allowed unwanted signal level can then be as great as 126.2 dB(W/6 MHz) for no more than 5 s (using the radar with the narrowest bandwidth given in Table 1). Long-term protection crit
33、erion It would seem reasonable that the radar error becomes more important over increasingly longer periods of time. For periods up to 1 min in duration it should be assumed that an increase in the angle error, due to an unwanted signal, should not exceed 5%. The long-term criterion is then an allow
34、ed unwanted signal level of 136.1 dB(W/6 MHz) for no more than 60 s. 1It is assumed here, for simplicity, that interfering signals will be interpreted by the victim receiver as an increase in the noise power in the IF stages. The actual response by radar systems may need to be considered, but is beyond the scope of this generalized treatment.
