1、 Rec. ITU-R M.1461-1 1 RECOMMENDATION ITU-R M.1461-1*Procedures for determining the potential for interference between radars operating in the radiodetermination service and systems in other services (Question ITU-R 226/8) (2000-2003) Summary This Recommendation provides guidance and procedures for
2、determining the potential for interference between radars operating in the radiodetermination service and systems in other services. The ITU Radiocommunication Assembly, considering a) that antenna, signal propagation, target detection, and large necessary bandwidth characteristics of radar to achie
3、ve their functions are optimum in certain frequency bands; b) that the technical characteristics of radars operating in the radiodetermination service are determined by the mission of the system and vary widely even within a band; c) that the radionavigation service is a safety service as specified
4、by the Radio Regulations (RR) No. 4.10 and harmful interference to it cannot be accepted; d) that considerable radiolocation and radionavigation spectrum allocations (amounting to about 1 GHz) have been removed or downgraded since WARC-79; e) that some ITU-R technical groups are considering the pote
5、ntial for the introduction of new types of systems (e.g., fixed wireless access and high-density fixed and mobile systems) or services in bands between 420 MHz and 34 GHz used by radars in the radiodetermination service; f) that representative technical and operational characteristics of systems ope
6、rating in bands allocated to the radiodetermination service are required to determine the feasibility of introducing new types of systems; g) that procedures and methodologies are needed to analyse compatibility between radars operating in the radiodetermination service and systems in other services
7、, *This Recommendation should be brought to the attention of the International Maritime Organization (IMO), the International Civil Aviation Organization (ICAO), the International Maritime Radio Committee (CIRM) and the World Meteorological Organization (WMO). 2 Rec. ITU-R M.1461-1 recommends 1 that
8、 the procedures in Annex 1 provide guidance for determining the potential for interference between radars operating in the radiodetermination service and systems in other services; 2 that those radar characteristics contained in appropriate ITU-R Recommendations be used for the frequency band under
9、study. NOTE 1 This Recommendation will be revised as more detailed information becomes available. Annex 1 Procedures for determining the potential for interference between radars operating in the radiodetermination service and systems in other services 1 Introduction Analysis procedures have been de
10、veloped. Because of the high transmitter output power (50 kW to several MW) and antenna gain (30 to 45 dBi) of radars operating in the radiodetermination service (hereafter simply referred to as radars), compatibility between radars and systems in other services is largely determined by analysing th
11、e effects of the emissions from radars on receiving functions of other services. Therefore, this analysis procedure primarily addresses the methods to assess the potential for interference from radars. In addition, potential desensitization of radar receivers by emissions from modulated continuous-w
12、ave (CW) systems in other services is briefly discussed. By the nature of the missions of radars, many are mobile and cannot be constrained to prescribed areas of operation. Also, the mission of radars often requires frequency agility and utilize the entire allocated band. But when radars are antici
13、pated to operate in certain areas in proximity to other systems, the potential for interference can be assessed using the procedures contained in this Recommendation. 2 Interference from radars to systems of other services Investigations of several interference cases have identified two primary elec
14、tro-magnetic interference coupling mechanisms between high power radar systems and other services. These interference coupling mechanisms are receiver front-end overload and radar transmitter emissions coupled through the receiver IF passband. Discussion of the interference mechanisms are provided b
15、elow. 2.1 Receiver front-end overload This interference mechanism occurs when energy from the fundamental frequency (necessary emissions) of an undesired signal saturates the victim receiver front-end (low noise amplifier (LNA) in some systems), resulting in gain compression of the desired signal su
16、fficient to degrade receiver performance. Receiver front-end overload is typically a result of inadequate RF selectivity in the front-end of the victim receiver. Rec. ITU-R M.1461-1 3 2.1.1 Assessing the potential for receiver front-end overload The input threshold at which receiver front-end overlo
17、ad occurs is a function of the 1 dB gain compression (saturation) level and the gain of the receiver front-end or LNA. Specifically: T = C G (1) where: T : input threshold at which receiver front-end overload occurs (dBm) C : output 1 dB gain compression (saturation) level of the receiver front-end
18、or LNA (dBm) G : gain of the receiver front-end or LNA at the radar fundamental frequency (dB). For example, if the receivers use LNAs with gains of 50 to 65 dB and they have an output 1 dB compression level of +10 dBm, the range of values for T is 55 dBm to 40 dBm, depending on the gain of the LNA.
19、 A potential for interference from receiver front-end overload will exist whenever: RFTFDRTI = (2) where: IT: peak radar signal level at the antenna output or receiver input that causes receiver front-end overload (dBm) T : input threshold at which receiver front-end overload occurs (dBm) FDRRF: fre
20、quency dependent rejection of the radar fundamental from any RF selectivity that may be ahead of the receiver RF amplifier (LNA) or that may be inherent in the RF amplifier (LNA) itself. Equation (3) can be used to determine whether receiver front-end overload is likely when radars operate within pa
21、rticular distances of other stations and are separated in frequency by certain amounts: PRTRTTLLLGGPI += (3) where: I : peak power of radar pulses, at the radars fundamental frequency, at the receiving antenna output or receiver input (dBm) PT: peak power of the radar transmitter (dBm) GT: main beam
22、 antenna gain of the radar (see Note 1) (dBi) GR: receiver antenna gain in the direction of the radar station under analysis (dBi) LT: insertion loss in the radar station transmitter (dB) (2 dB assumed) LR: insertion loss in the victim receiver (dB) LP: propagation path loss between transmitting and
23、 receiving antennas (dB). 4 Rec. ITU-R M.1461-1 In determining the propagation path loss, appropriate propagation models and possible indirect coupling should be used taking into consideration antenna heights and terrain when appropriate. If the calculated peak power of the radar pulses, at the fund
24、amental frequency, I, exceed the threshold at which receiver front-end overload occurs, IT, necessary steps to ensure compatibility need to be taken. NOTE 1 Interference cases of radar transmitter emissions causing receiver front-end overload for radar mainbeam coupling have been documented. Therefo
25、re, it is recommended that the radar mainbeam gain be used in assessing the maximum potential for interference caused by receiver front-end overload. 2.2 Radar transmitter emission coupling This interference mechanism occurs when energy emitted from the radar transmitter falls within the IF passband
26、 of the receiver. This energy then passes through the receiver chain with little or no attenuation. When the radar emission levels in the receiver passband are high relative to the desired signal level, performance degradation to the receiver can occur. 2.2.1 Assessing the potential for radar transm
27、itter emission interference The initial step in assessing compatibility is the determination of the signal level at which the receiver performance starts to degrade, IT. IT= I/N + N (4) where: I/N : interference-to-noise ratio at the detector input (IF output) necessary to maintain acceptable perfor
28、mance criteria (dB) N : receiver inherent noise level (dBm) (N = 144 dBm + 10 log BIF(kHz) + NF or N = 168.6 dBm + 10 log BIF(kHz) + 10 log T) where: BIF: receiver IF bandwidth (kHz) NF : receiver noise figure (dB) T : system noise temperature (K). Also, the signal level at which a receiver starts t
29、o degrade, IT,can be calculated using equation (5): IT= C (C/I) (5) where: C : desired carrier signal level at the antenna output (receiver input) (dBm) C/I : carrier-to-interference ratio at the predetector input (IF output) necessary to maintain acceptable performance criteria (dB). Equation (6) c
30、an be used to determine whether radar transmitter emission interference is likely when radars operate within particular distances of other stations and are separated in frequency by certain amounts. I = PT+ GT+ GR LT LR LP FDRIF(6) Rec. ITU-R M.1461-1 5 where: I : peak power of the radar pulses at t
31、he receiver (dBm) PT: peak power of the radar transmitter under analysis (dBm) GT: main beam antenna gain of the radar under analysis (see Note 2) (dBi) GR: receiver antenna gain in the direction of the radar station under analysis (dBi) LT: insertion loss in the radar station transmitter (dB) LR: i
32、nsertion loss in the victim receiver (dB) LP: propagation path loss between transmitting and receiving antennas (dB) FDRIF: frequency-dependent rejection produced by the receiver IF selectivity curve on an unwanted transmitter emission spectra (dB). NOTE 2 Interference cases of radar transmitter emi
33、ssions causing receiver degradation for radar mainbeam coupling have been documented. Therefore, it is recommended that the radar mainbeam gain be used in assessing the maximum potential for interference caused by radar transmitter emissions in the receiver IF passband. The FDR value to be used in e
34、quation (6) can be determined from Recommendation ITU-R SM.337. The FDR can be divided into two terms, the on-tune rejection (OTR) and the off-frequency rejection (OFR), the additional rejection which results from off-tuning the radar and the receiver. )()( fOFROTRfFDRIF+= (7) For CW and phase-coded
35、 pulsed signals, the OTR factor is given by: OTR = 0 for BR BT(8) OTR = 20 log (BT/ BR) for BR1 (11) where: T : chirped pulse width (s) BC: transmitter chirped bandwidth during the pulsewidth, T (Hz). Calculation of the OFR requires the IF response and the emission spectrum characteristics of the ra
36、dar transmitter. The ITU-R has provided methods for calculating the emission spectrum characteristics of CW pulsed and chirped pulsed radars. If information is not available for radar transmitter rise and fall time characteristics, the radar emission envelops should be calculated for nominal rise an
37、d fall times of 0.1 s. The spurious emission levels from radar transmitters are a function of the transmitter output device. Representative spurious emission levels for various radar 6 Rec. ITU-R M.1461-1 output devices are contained in Recommendation ITU-R M.1314. Since many radars have high transm
38、itter power and antenna gains, large frequency separations, guardbands, may be required to ensure compatibility. In determining the propagation path loss, appropriate propagation models and possible indirect coupling should be used taking into consideration antenna heights and terrain when appropria
39、te. If the calculated peak power of the radar pulses, at the receiver input, I, exceed the threshold at which receiver performance degrades, IT, necessary steps to ensure compatibility need to be taken. 3 Interference to radars from systems in other services Introduction Two primary electromagnetic
40、interference coupling mechanisms between the radar system and interfering signals from other services exist. The first mechanism is caused by front-end overload causing saturation, and the generation of intermodulation products. The second is interfering emissions within the receiver IF passband lea
41、ding to desensitization and degradation of performance resulting in an overall lowered quality radar data output. 3.1 Receiver front-end overload 3.1.1 Front-end saturation This interference mechanism occurs when energy from an undesired signal saturates the LNA of the radar receiver front-end resul
42、ting in gain compression of the desired signal which is sufficient to degrade receiver performance. The input threshold at which receiver front-end overload occurs is a function of the 1 dB gain compression (saturation) level and the gain of the receiver front-end. Given a radar receiver with front-
43、end RF bandwidth, BRF, and 1 dB compression input power P1 dB(dBm), the total interference power inside BRFentering the radar receiver must not exceed: PI, RF max= P1 dB+ ksat= C G + ksatdBm (12) where: PI, RF max: maximum allowed total interference power inside the RF-bandwidth (dBm) ksat: saturati
44、on margin (dB), to be determined individually for each radar and interference type (ksatis generally negative) P1 dB: defined as the 1 dB-input power compression point (dBm), i.e. when the gain of the whole receiver chain has decreased by 1 dB C : output 1 dB gain compression (saturation) level of t
45、he receiver front-end or LNA (dBm) G : gain of the receiver front-end at the fundamental frequency of the potential interference source (dB). For example, if the receivers use LNAs with a gain of 60 dB and they have an output 1 dB compression level of +10 dBm, the value for P1 dBis 10 60 = 50 dBm. R
46、ec. ITU-R M.1461-1 7 Fulfilment of equation (12) is essential in order to avoid driving the receiver close to or into saturation and thereby to maintain sufficient dynamic range for the radar echo signal itself. Moreover, the fraction of interference power falling into the radar receivers IF bandwid
47、th must also fulfil the requirements laid down in relevant ITU Recommendations. A potential for receiver front-end overload from interference will exist whenever: RFmaxRFITFDRPI ,(13) where: IT: interference signal level at the receiver input that causes receiver front-end overload (dBm) FDRRF: freq
48、uency dependent rejection of the interference source by any RF selectivity that may be ahead of the receiver RF amplifier (LNA) or that may be inherent in the RF amplifier (LNA) itself. Received interference power, aggregated over the full RF bandwidth, must not be higher than the level which causes
49、 output power of that particular element in the receiver chain which first goes into saturation to retain a sufficient separation below the 1 dB compression point. This is to limit the reduction in dynamic range and to prevent 3rd-order intermodulation products exceeding the acceptable I/N in the receivers IF bandwidth. Equation (13) can be used to determine the interference signal level at the input of the first amplifier stage of the receiver chain when interference sources operate within particular distances of other stations and are separated in frequenc
