1、 Recommendation ITU-R M.1177-4(04/2011)Techniques for measurement of unwanted emissions of radar systemsM SeriesMobile, radiodetermination, amateurand related satellite servicesii Rec. ITU-R M.1177-4 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient a
2、nd economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are perfo
3、rmed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms t
4、o be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be fo
5、und. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, ra
6、diodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management
7、 SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2011 ITU 2011 All rights reserved. No part of t
8、his publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R M.1177-4 1 RECOMMENDATION ITU-R M.1177-4*Techniques for measurement of unwanted emissions of radar systems (Question ITU-R 202/5) (1995-1997-2000-2003-2011) Scope This Recommendation provides tw
9、o techniques for the measurement of radiated radar unwanted emissions. It should be used to measure the spurious domain emissions and to check emission power against limits specified in Appendix 3 (Section II) of the Radio Regulations (RR), or to measure the level of unwanted emissions falling withi
10、n the out-of-band domain. The ITU Radiocommunication Assembly, considering a) that both fixed and mobile radar stations in the radiodetermination service are widely implemented in bands adjacent to and in harmonic relationship with other services; b) that stations in other services are vulnerable to
11、 interference from radar stations with unwanted emissions with high peak power levels; c) that many services have adopted or are planning to adopt digital modulation systems which are more susceptible to interference from radar unwanted emissions; d) that under the conditions stated in considering a
12、) through c), interference to stations in other services may be caused by a radar station with unwanted emissions with high peak power levels; e) that Recommendation ITU-R SM.329 specifies the maximum values of unwanted emissions in the spurious emission domain from radio transmitters; f) that Recom
13、mendation ITU-R SM.1541 specifies the generic limits for unwanted emissions in the out-of-band domain, recommends 1 that measurement techniques as described in Annex 1 should be used to provide guidance in quantifying radiated unwanted emission levels from radar stations operating above 400 MHz; 2 t
14、hat measurement techniques as described in either Annex 1 or Annex 2 should be used, as appropriate based upon radar design, to provide guidance in measuring radiated unwanted emission levels for radar stations operating between 50 MHz and 400 MHz; 3 that measurement techniques described in Annex 2
15、should be used to provide guidance in quantifying radiated unwanted emission levels from radar stations operating below 50 MHz. *This Recommendation should be brought to the attention of the International Maritime Organization (IMO), the International Civil Aviation Organization (ICAO), the Internat
16、ional Maritime Radio Association (CIRM), the World Meteorological Organization (WMO) and Radiocommunication Study Groups 1 and 4. 2 Rec. ITU-R M.1177-4 Annex 1 Measurement of unwanted emissions of radar systems as detailed in recommends 1 and 2 1 Introduction Two measurement techniques known as the
17、direct and indirect methods are described. The direct measurement method is recommended and measures unwanted emissions from all radars including those that preclude measurements at intermediate points within the radar transmitters. Examples include those which use distributed-transmitter arrays bui
18、lt into (or comprising) the antenna structure. The indirect method separately measures the components of the radar and then combines the results. The recommended split of the radar is to separate the system after the Rotating Joint (Ro-Jo) and thus to measure the transmitter output spectrum at the o
19、utput port of the Ro-Jo and to combine it with the measured antenna gain characteristics. 2 Reference bandwidth For radar systems, the reference bandwidth, Bref, used to define unwanted emission limits (Recommendations ITU-R SM.329 and ITU-R SM.1541, and RR Appendix 3) should be calculated for each
20、particular radar system. For the four general types of radar pulse modulation utilized for radionavigation, radiolocation, acquisition, tracking and other radiodetermination functions, the reference bandwidth values are determined using the following formulas: for fixed-frequency, non-pulse-coded ra
21、dar, one divided by the radar pulse length (e.g. if the radar pulse length is 1 s, then the reference bandwidth is 1/1 s = 1 MHz); for fixed-frequency, phase-coded pulsed radar, one divided by the phase chip length (e.g. if the phase coded chip is 2 s long, then the reference bandwidth is 1/2 s = 50
22、0 kHz); for FM or chirped radar, the square root of the quantity obtained by dividing the chirp bandwidth (MHz) by the pulse length (s) (e.g. if the FM is from 1 250 MHz to 1 280 MHz or 30 MHz during the pulse of 10 s, then the reference bandwidth is (30 MHz/10 s)1/2= 1.73 MHz); for radars operating
23、 with multiple waveforms the reference bandwidth is determined empirically from observations of the radar emission. The empirical observation is performed as follows: the measurement system receiver is tuned to one of the fundamental frequencies of the radar, or is tuned to the centre frequency with
24、in the chirp range of the radar. The measurement system bandwidth is set to the widest available value, and the received power level from the radar in this bandwidth is recorded. The measurement bandwidth is then progressively narrowed, and the received power level is recorded as a function of the b
25、andwidth. The end result is a graph or table showing measured power as a function of measurement system bandwidth. The required bandwidth is the smallest bandwidth in which the full power level is still observed and the reference bandwidth can be calculated from a knowledge of the impulse response o
26、f the measurement receiver using the factor, measurement bandwidth ratio (MBR), as described below. If a reduction in power level is observed immediately, then the widest available bandwidth should be used. Rec. ITU-R M.1177-4 3 In all cases, where the bandwidths above are greater than 1 MHz, then a
27、 reference bandwidth, Bref, of 1 MHz should be used. 3 Measurement bandwidth and detector parameters The measurement bandwidth, Bm, is defined as the impulse bandwidth of the receiver and is greater than the IF bandwidth, Bif, (sometimes referred to as resolution bandwidth for spectrum analyzers). T
28、he measurement bandwidth, Bm, may be derived from the following equation: MBRBBifm= The MBR needs to be determined for the measurement receiver being used. MBR is approximately 3/2 for a 3 dB IF bandwidth Gaussian filter as typically used in many commercial spectrum analyzer receivers (in some instr
29、uments the IF bandwidth is defined at the 6 dB point). An appropriate receiver IF bandwidth should be selected to give one of the following recommended measurement bandwidths. Measurement bandwidth Bm1 (1/T ) for fixed-frequency, non-pulse-coded radars, where T is the pulselength (e.g. if the radar
30、pulse length is 1 s, then the measurementbandwidth should be = 1/(1 s) = 1 MHz). (1/t ) for fixed-frequency, phase-coded pulsed radars, where t is the phase-chip length (e.g. if the radar transmits 26 s pulses, each pulse consisting of13 phase coded chips that are 2 s in length, then the measurement
31、bandwidth should be 1/(2 s) = 500 kHz). (Bc/T )1/2for swept-frequency (FM, or chirp) radars, where Bcis the range offrequency sweep during each pulse and T is the pulse length (e.g. if radarsweeps (chirps) across the frequency range of 1 250-1 280 MHz (= 30 MHzof spectrum) during each pulse, and if
32、the pulse length is 10 s, then themeasurement bandwidth should be (30 MHz)/(10 s)1/2= 3 MHz 1.73 MHz. In accordance with footnote 1a measurement bandwidth close tobut less than or equal to 1 MHz should be used in this example. the result of a measurement is as follows: for radars operating with mult
33、iplewaveforms the measurement bandwidth is determined empirically fromobservations of the radar emission. The empirical observation is performedas follows: the measurement system receiver is tuned to one of thefundamental frequencies of the radar, or is tuned to the centre frequencywithin the chirp
34、range of the radar. The measurement system bandwidth isset to the widest available value, and the received power level from the radarin this bandwidth is recorded. The measurement bandwidth is thenprogressively narrowed, and the received power level is recorded asa function of the bandwidth. The end
35、 result is a graph or table showingmeasured power as a function of measurement system bandwidth.The appropriate measurement bandwidth will be the bandwidth where thefirst reduction of the full power level is observed. If a reduction in powerlevel is observed immediately, then the widest available me
36、asurementbandwidth should be used. 1In all cases, if the above derived measurement bandwidth is greater than 1 MHz, then the corrections described in 3.2 should be used. 4 Rec. ITU-R M.1177-4 Video bandwidth measurement system bandwidth. Detector positive peak. 3.1 Measurements within the out-of-ban
37、d domain Within the out-of-band (OoB) domain, the limits given in Recommendation ITU-R SM.1541 are defined in dBpp. This is a relative power measurement and an IF bandwidth leading to a measurement bandwidth less than the reference bandwidth should be used. Even if the measurement bandwidth is less
38、than the reference bandwidth no correction needs to be done, since both the peak of the spectrum and the data points within the OoB domain are measured using the same measurement bandwidth Bm. Measurements should generally be made using a bandwidth that is close to but less than the specified refere
39、nce bandwidth. This approach will minimize the measurement time but it also causes some broadening of the measured spectrum. Thus in marginal situations, where measurement of the true close in spectrum shape may be important, it is recommended that the close-in region within the OoB domain should be
40、 re-measured using a maximum bandwidth of 0.2/T or 0.2/t as appropriate. 3.2 Measurements within the spurious domain 3.2.1 Correction of the measurement within the spurious domain Where the measurement bandwidth, Bm, differs from the reference bandwidth, Bref, a correction factor needs to be applied
41、 to the measurements conducted within the spurious domain to express the results in the reference bandwidth. Then the following correction factor should be applied: Spurious level, Bref= Spurious level (measured in Bm) + 10 log(Bref/Bm) NOTE 1 This correction factor should be used except where it is
42、 known that the spurious is not noise-like, where a factor between 10 and 20 log(Bref/Bm) may apply and may be derived by measurements in more than one bandwidth. In all cases the most precise result will be obtained using a measurement bandwidth (Bm) equal to the reference bandwidth. For radars ope
43、rating above 1 GHz the reference bandwidth (Bref) is 1 MHz. 3.2.2 Correction of the measurement data to the peak envelope power Within the spurious domain, the limits given in RR Appendix 3 are defined in a reference bandwidth, Bref, with respect to the peak envelope power (PEP). Data recorded in dB
44、pp within the spurious domain must be referenced to the PEP (and not the spectrum peak observed in dBpp). The PEP is approximated using the following correction formulae: For continuous wave (CW) and phase coded pulses: PEP = Pmeas+ 20 log(Bpep/Bm) for Bpep BmFor swept-frequency (FM or chirp) pulsed
45、 radars: 1/)(for)/(log(1022instantaneous measurement dynamic range). The final element in the RF front-end is an LNA. An LNA is installed as the next element in the signal path after the preselector. The low-noise input characteristic of the LNA provides high sensitivity to low-amplitude spurious ra
46、dar emissions, and its gain allows for the noise figure of the rest of the measurement system (e.g. a length of transmission line and a spectrum analyzer). The sensitivity and dynamic range of the measurement system are optimized by proper selection of LNA gain and noise figure characteristics. It i
47、s desirable to minimize noise figure while providing enough gain to allow for all measurement circuitry after the LNA (essentially the RF line loss after the front-end, plus the noise figure of the spectrum analyzer circuitry). Ideally, the sum of the LNA gain and noise figure (which is the excess n
48、oise produced by the LNA with a 50 termination on its input) should be approximately equal to the noise figure of the remaining measurement system. Typical spectrum analyzer noise figures are 25-45 dB (varying as a function of frequency), and transmission line losses may typically be 5-10 dB, depend
49、ing upon the quality and the length of the line. As a result of the variation in measurement system noise figure as a function of frequency, a variety of LNAs used in frequency octaves (e.g. 1-2 GHz, 2-4 GHz, 4-8 GHz, 8-18 GHz, 18-26 GHz and 26-40 GHz) may be required. Each LNA can be optimized for gain and noise figure within each frequency octave. This also helps match LNAs to octave breaks between various YIG filters (e.g. 0.5-2 GHz, 2-18 GHz, etc.). Use of an LNA after the preselector (and, if required, a cascaded LNA at the
