1、 Recommendation ITU-R P.372-12 (07/2015) Radio noise P Series Radiowave propagation ii Rec. ITU-R P.372-12 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, includi
2、ng 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 performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies s
3、upported 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 to be used for the submission of patent statements and licensing declarations by patent holder
4、s 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 found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/e
5、n) 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, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio ast
6、ronomy 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 SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary
7、and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2015 ITU 2015 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU
8、. Rec. ITU-R P.372-12 1 RECOMMENDATION ITU-R P.372-12 Radio noise* (Question ITU-R 214/3) (1951-1953-1956-1959-1963-1974-1978-1982-1986-1990-1994-2001-2003-2007-2009-2013-2015) Scope Recommendation ITU-R P.372 provides information on the background levels of radio-frequency noise in the frequency ra
9、nge from 0.1 Hz to 100 GHz. It takes account of noise due to lightning, to man-made sources, to the galaxy and to the temperature of the lower atmosphere. Noise figures or temperatures are given to provide a basis for the estimation of system performance. Keywords: radio noise, noise factor, noise t
10、emperature The ITU Radiocommunication Assembly, considering a) that radio noise sets a limit to the performance of radio systems; b) that the effective antenna noise figure, or antenna noise temperature, together with the amplitude probability distribution of the received noise envelope, are suitabl
11、e parameters (almost always necessary, but sometimes not sufficient) for use in system performance determinations and design; c) that it is generally inappropriate to use receiving systems with noise figures less than those specified by the minimum external noise; d) that knowledge of radio emission
12、 from natural sources is required in evaluation of the effects of the atmosphere on radiowaves; allocation of frequencies to remote sensing of the Earths environment, recommends that the following information should be used where appropriate in radio system design and analysis: 1 Sources of radio no
13、ise Radio noise is defined in Recommendation ITU-R V.573 as follows: radio (frequency) noise; A time-varying electromagnetic phenomenon having components in the radio-frequency range, apparently not conveying information and which may be superimposed on, or combined with, a wanted signal. * A comput
14、er program associated with the characteristics and applications of atmospheric noise due to lightning, of man-made noise and of galactic noise (at frequencies below about 100 MHz), described in this Recommendation, is available from that part of the ITU-R website dealing with Radiocommunication Stud
15、y Group 3. 2 Rec. ITU-R P.372-12 Note 1 In certain cases a radio-frequency noise may convey information on some characteristics of its source, for example its nature and location. Note 2 An aggregate of signals may appear as radio-frequency noise, when they are not separately identifiable. Recommend
16、ation ITU-R P.372 provides data on radio noise external to the radio receiving system which derives from the following causes: radiation from lightning discharges (atmospheric noise due to lightning); aggregated unintended radiation from electrical machinery, electrical and electronic equipments, po
17、wer transmission lines, or from internal combustion engine ignition (man-made noise); emissions from atmospheric gases and hydrometeors; the ground or other obstructions within the antenna beam; radiation from celestial radio sources. NOTE 1 The estimates of radio noise levels given here are for the
18、 background noise level in the absence of other signals, whether intentionally or unintentionally radiated, so that noise or signals due to unwanted co-channel transmissions or due to spurious emissions from individual transmitting or receiving systems are not considered in this Recommendation. NOTE
19、 2 In the case of man-made noise, the data provided are intended to be representative of the environmental category, with typical levels of electrical and electronic activity operating normally, at typical distances for that environment. 2 Terms for the specification of noise intensity and their int
20、errelationship The noise factor, f, for a receiving system is composed of a number of noise sources at the receiving terminal of the system. Both internal and external noise must be considered. The only appropriate reference point for the overall operating noise factor for a radio receiving system i
21、s the input of an equivalent loss-free receiving antenna. (The terminals of this lossless antenna do not exist physically.) For receivers free from spurious responses, the system noise factor is given by: f = fa + ( fc 1) + lc ( ft 1) + lc lt ( fr 1) (1) where: fa : the external noise factor defined
22、 as: bTk pf na 0(2) NOTE 1 Fa is the external noise figure defined as: Fa = 10 log fa dB pn : available noise power from an equivalent lossless antenna k : Boltzmanns constant = 1.38 1023 J/K T0 : reference temperature (K) taken as 290 K b : noise power bandwidth of the receiving system (Hz) lc : an
23、tenna circuit loss (available input power/available output power) lt : transmission line loss (available input power/available output power) fr : noise factor of the receiver. Rec. ITU-R P.372-12 3 NOTE 2 Fr is the receiver noise figure defined as: Fr = 10 log fr dB fc is the noise factor associated
24、 with the antenna circuit losses, 0)1(1 TTlf ccc (3) ft is the noise factor associated with the transmission line losses, 0)1(1 TTlf ttt (4) where: Tc: actual temperature (K) of the antenna and nearby ground and Tt: actual temperature (K) of the transmission line. If Tc = Tt = T0, equation (1) becom
25、es f = fa 1 + fc ft fr (5) Equation (2) can be written: Pn = Fa + B 204 dBW (6) where: Pn = 10 log pn : available power (W) B = 10 log b, and 204 = 10 log k T0. For a short (h about 1 GHz), Fa values are quite low and only the higher magnitude pulses appear above the receivers noise threshold. Descr
26、iptions here can take the form of peak value for a given time period, exceedance probabilities at these higher levels, pulse count at a specified level, etc. 3 Noise levels as a function of frequency The following three figures and related discussion specify the expected values of Fa in the frequenc
27、y range 0.1 Hz to 100 GHz along with other noise levels of interest. The three figures display the relative magnitude of the noise types specified in 1. Additional details for the various noise types are given in later sections of this Recommendation. Figure 1 covers the frequency range 0.1 Hz to 10
28、 kHz. The solid curve is the minimum expected hourly median values of Fa based on measurements (taking into account the entire Earths surface, all seasons and times of day) and the dashed curve gives the maximum expected values. Note that in this frequency range there is very little seasonal, diurna
29、l, or geographic variation. The larger variability in the 100-10 000 Hz range is due to the variability of the Earth-ionosphere wave-guide cutoff. FIGURE 1 Fa minimum and maximum versus frequency (101 to 104 Hz) P. 0 3 7 2 - 0 12 . 9 1 0322 . 9 1 030282 . 9 1 0262 . 9 1 0242 . 9 1 0222 . 9 1 0202 .
30、9 1 0182 . 9 1 0162 . 9 1 0142 . 9 1 0F(dB)aFreq u en cy (H z)A:B:C:mi cro p u l s at i o n smi n i mu m v al u e ex p ec t ed o f at mo s p h eri c n o i s emax i mu m v al u e ex p ec t ed o f at mo s p h eri c n o i s eACB120140160180200220240260280300512 5102 5 2 5 2 52102103104101Ta(K)Ta(K)Rec.
31、 ITU-R P.372-12 5 Figure 2 covers the frequency range 104 to 108 Hz, i.e. 10 kHz to 100 MHz for various categories of noise. The minimum expected noise is shown by the solid curves. For atmospheric noise, the minimum values of the hourly medians expected are taken to be those values exceeded 99.5% o
32、f the hours and the maximum values are those exceeded 0.5% of the hours. For the atmospheric noise curves, all times of day, seasons, and the entire Earths surface have been taken into account. FIGURE 2 Fa versus frequency (104 to 108 Hz) P. 0 3 7 2 - 0 22 . 9 1 0102 . 9 1 082 . 9 1 022 . 9 1 0202 .
33、 9 1 0182 . 9 1 0162 . 9 1 0142 . 9 1 0122 . 9 1 062 . 9 1 04F(dB)aFreq u en cy (H z)ABCDE: at mo s p h eri c n o i s e, v al u e ex ce ed ed 0 . 5 % o f t i me: at mo s p h eri c n o i s e, v al u e ex ce ed ed 9 9 . 5 % o f t i me: man -mad e n o i s e, q u i et rec ei v i n g s i t e: g al ac t i
34、 c n o i s e: med i an are a man -mad e n o i s eci t ymi n i mu m n o i s e l ev el ex p ec t edAEDCB0204060801001201401601802 5 2 5 2 5 2 5104105106107108Ta(K)Figure 3 covers the frequency range 108 to 1011 Hz, i.e. 100 MHz to 100 GHz. Again the minimum noise is given by solid curves, while some o
35、ther noises of interest are given by dashed curves. The majority of the results shown in the three figures are for omni-directional antennas (except as noted on the figures). For directional antennas, however, studies have indicated that at HF (for example), for atmospheric noise from lightning for
36、very narrow beam antennas, there can be as much as 10 dB variation (5 dB above to 5 dB below the average Fa value shown) depending on antenna pointing direction, frequency and geographical location. For galactic noise, the average value (over the entire sky) is given by the solid curve labelled gala
37、ctic noise (Figs 2 and 3). Measurements indicate a 2 dB variation about this curve, neglecting ionospheric shielding. The minimum galactic noise (narrow beam antenna towards galactic pole) is 3 dB below the solid galactic noise curve shown on Fig. 3. The maximum galactic noise for narrow beam antenn
38、as is shown via a dashed curve in Fig. 3. 4 Noise from atmospheric gases and the Earths surface Noise from individual sources such as the Sun, atmospheric gases, the Earths surface, etc., are usually given in terms of a brightness temperature, Tb. The antenna temperature, Ta, is the convolution of t
39、he antenna pattern and the brightness temperature of the sky and ground. 6 Rec. ITU-R P.372-12 For antennas whose patterns encompass a single source, the antenna temperature and brightness temperature are the same (curves C, D and E of Fig. 3, for example). FIGURE 3 Fa versus frequency (108 to 1011
40、Hz) P. 0 3 7 2 - 0 3F(dB)aFreq u en cy (H z)(1 G H z)2 . 9 1 02 . 92 . 9 1 062 . 9 1 052 . 9 1 042 . 9 1 032 . 9 1 022 . 9 1 012 . 9 10 21ABCDEF: es t i mat ed med i an area man -mad e n o i s e ci t y : g al act i c n o i s e: g al act i c n o i s e (t o w ard g al act i c cen t re w i t h i n fi n
41、 i t el y n arro w b eamw i d t h ): q u i et Su n ( b eamw i d t h d i rect ed at Su n ): s k y n o i s e d u e t o o x y g en an d w at er v ap o u r (v ery n arro w b eam an t en n a);u p p er cu rv e, 0 el ev at i o n an g l e; l o w er cu rv e, 9 0 el ev at i o n an g l e: : b l ack b o d y (co
42、 s mi c b ack g ro u n d ), 2 . 7 Kmi n i mu m n o i s e l ev el ex p ect edAE (0 )DCBE (9 0 )F2 5 2 5 2 510910810101011010203040 4 0 3 0 2 0 1 0Ta(K)Figures 4 and 5 show the brightness temperature of the atmosphere for a ground-based receiver excluding the cosmic noise contribution of 2.7 K or othe
43、r extra-terrestrial sources for frequencies between 1 and 340 GHz in the first instance and 1 and 60 GHz in the second. The curves are calculated using a radiative transfer program for seven different elevation angles and an average atmosphere (7.5 g surface water vapour density, surface temperature
44、 of 288 K, and a scale height of 2 km for water vapour). The “U.S. Standard Atmosphere, 1976” is used for the dry atmosphere. A typical water vapour contribution is added above the tropopause. Rec. ITU-R P.372-12 7 FIGURE 4 Brightness temperature (clear air) for 7.5 g/m3 water vapour concentration (
45、surface temperature and pressure equal to 15C and 1 023 mb); is the elevation angle P.0372-04Brightness temperature (K)Frequency(GHz)01002003000100200300400106090300010206090305102060903051020609030051020609030=08 Rec. ITU-R P.372-12 FIGURE 5 Brightness temperature for clear air for 7.5 g/m3 of wate
46、r vapour concentration (expansion of abscissa scale of Fig. 4); is the elevation angle P.0372-05Brightness temperature (K)Frequency(GHz)0510152025303540455055601101000100200500 252050=010206090305Rec. ITU-R P.372-12 9 4.1 Radio noise due to the Earths atmosphere for earth stations In Earth-space com
47、munication, if the attenuation of the signal from a spacecraft transmitter to a receiver near the surface of the Earth is known, a good estimate of the brightness (i.e., sky noise) temperature for frequencies between 2 and 30 GHz in the direction of the propagation path from the receiver to the spac
48、ecraft transmitter can be obtained from the following formula: 1010 107.2101 AAmrb TT K (10) where: Tb : brightness temperature (K) at the ground station antenna A : total atmospheric attenuation excluding scintillation fading (dB) Tmr : atmospheric mean radiating temperature (K). When the surface t
49、emperature Ts (K) is known, the mean radiating temperature, Tmr, may be estimated for clear and cloudy weather as: smr TT 81.034.37 K (11) In the absence of local data an atmospheric mean radiating temperature, Tmr, of 275 K may be used for clear and rainy weather. A radiative transfer study including cloud effects has been carried out in
