Propagation Effects Handbook for Satellite Systems - DESCANSO ...

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6.8.3 sky Noise Due to Rain Kirchhoffts law applies to noise emission from rain as well as from atmospheric gases, but only to the absorption component of the rain attenuation and not to the scattered component. The scattered component increases with frequency, so that while Eq. (6.8-5) may be appropriate at 10 GHz, it will give too high a value at 70 GHz. Values of T~ due to rain may be estimated from the rain attenuation calculation techniques presented in Section 6.3. For example, to compute the cumulative statistics of Ts, first compute the cumulative attenuation statistics due to rain, and then use Eq. 6.8.5 to convert attenuation to apparent sky noise temperature. An example results The degrade of this process has been done for Rosman, NC at 20 GHz. The are given in Table 6.8-1. sky noise temperature (see last column of Table 6.8-1) will the overall system noise figure of the receiver system. For example, for a receiver with a 4 dB noise figure, the resultant noise figure for the rain rate corresponding to 0.01% of the year will be 5.4 dB, i.e., an increase of 1.4 dB. 6.8.4 Sample Calculations Two illustrative examples of application of the sky noise relationships for clear air and for rain are presented below. ExamDle 1. A land mobile satellite system downlink is to operate at 20 GHz with a service reliability of 95 % of the time. The receiver system noise temperature, exclusive of antenna noise, is 100 K. The elevation angle to the satellite is 60°. The median surface humidity is estimated at 7.5 g/m3. What is the required propagation margin? From Figure 6.8-3 we read T = 20 K for the parameters given above. For the worst .5 % of the time we arbitrarily double this value to T = 40 K. The gaseous attenuation for the link can be determined from the 6-136
-. Table 6.8-1. Cumulative Statistics of Sky Temperature Due to Rain. for Rosman, N.C. at 20 GHz. ‘Tm = - 275 K. # T ‘ERCENT OF POINT RAIN AVERAGE RAIN TOTAL RAIN SKY NOISE YEAR RATE VALUES RATE ATTENUATION* Temperature 0.001 102 mn/hr 89 mn/hr 47 dB 275 K I 0.002 86 77 40 275 0.005 64 60 30 275 0.01 49 47 23 274 0.02 35 35 16 269 0.05 22 24 11 252 NOTES : 0.l 15 17 7 224 0.2 9.5 11.3 4.6 180 0.5 5.2 6.7 2.6 123 1.0 3.0 4.2 1.5 82 2.0 1.8 2.7 O*93 53 * At 20 GHz the specific attenuation A = 0.06 Rave~*12 dB/km and for Rosman, N.C. the effective path length Is 5.1 kmto ATS-6. t For a ground temperature of 17°C = 63°F the Tm= 275 K. 6-137
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1 6.1 INTRODUCTION 6.1.1 purpose CH
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,s Table 6.1-1. Guide to Sample Cal
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I . . 6.1.4 Other Propagation Effec
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. . collisions at normal atmospheri
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D 1000 100 10 1 U.S. Standard Atmos
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Frequency (GHz) 10 15 20 30 40 80 1
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If PW is not available from local w
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. . The equivalent heights for oxyg
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m t TEMPERATURE rC) o 5 10 15 20 25
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6.3 PREDICTION OF CUMULATIVE STATIS
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LSTATION LOCATION AND ELEVATION STE
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The models require the following in
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I z za E 100 g w ~ z z K 50 a) ALL
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B . . . t- I I I I I 1 11/1 - . . .
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.- . 9 s@EQ - If Z S D, compute the
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1 0.02 0.05 0.2 0.5 4. Compute D: U
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I . ,. . ~ q 8 H v ~ 1.0 0.8 0.6 0.
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Step 6 Calculate the attenuation ex
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m I : STEP 1 SELECT CLIMATE ZONE FR
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9 10.OOOO 1.0000 0,1ooo 0.0100 0.00
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1 6.3.3 Estimates of Attenuation Gi
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● We now proceed exactly as in th
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STEP 1 GIVEN: STATION PARAMETERS SA
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. B . . . 4. Repeat the process for
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. . ● 100 10 1.0 .1 .01 . . RAIN
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not normally available~ but empiric
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● The intensity-duration-frequenc
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- GIVEN: STATION PARAMETERS OPERATI
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m I s 70 2(J I 10 0 a) BY SEASONS
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.“ ● change in rain rater the r
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m To x o 6 x(n wux!- (5 zawwvxw x 1
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● ✎ ✎ ✎ 10 1 0.1 0.01 0 . -
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● ✎ ✎ ✎ appears to be gener
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6.4.2.3 Statistics of Microwave Eff
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● For each hour’s observations,
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Plots of noise temperature and atte
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.- I where Lf is the fog extent~ in
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than a minute and on spatial scales
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. . . 022 = angle-of-arrival varian
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B . . Figure 6.5-2 represents the a
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- . . , 1 I t , 3 , I 1 # 1 1 aJ 0a
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I . . -. % i ! ~ * 76.00 I h 60.00
Page 85 and 86: I where the constants are the same
Page 87 and 88: .U . . \ Table 6.5-1. Fading Data P
Page 89 and 90: o -5C \ A — . \ \ \ \ N- ● ●
Page 91 and 92: I 1 \ 0,, FADE DEPTHS I 1 l.d 0.1 1
Page 93 and 94: 9 m ELEVATION ANGLE [DEGREESI ELEVA
Page 95 and 96: Figure 6.5-12 is an example for thi
Page 97 and 98: equal. The fade distributions resul
Page 99 and 100: m . ANTENNA BEAMVVID~ (DEG) d o 0 w
Page 101 and 102: . . 6.5.5.2.2 Spatial Diversity. Pa
Page 103 and 104: fluctuation power at 1 Hz is on the
Page 105 and 106: develops (Pruppacher and Pitter-197
Page 107 and 108: .8 where: f = frequency, in GHz r =
Page 109 and 110: B . k 11.7 26 \ QHz DATA, CTS A VPl
Page 111 and 112: \ for the 11.7 GHz CTS beacon at 50
Page 113 and 114: ● these do not correlate well wit
Page 115 and 116: . However the XPD dependence on ele
Page 117 and 118: -. 50 40 30 20 10 0 . T(XPD < ABCIS
Page 119 and 120: 9 electrostatic fields discharge ra
Page 121 and 122: , f w m I
Page 123 and 124: . XPD 2 = XPD1 - 20 lo91~ f ~ 1 0.4
Page 125 and 126: ● 3.0 14 0.6 0.3 0,1 0.0s 0.03 0.
Page 127 and 128: where, for example, for the frequen
Page 129 and 130: L .- . ., not appear to be sufficie
Page 131 and 132: D ‘1 may be considered to be rece
Page 133 and 134: D - 0 m a 80 60 40 20 0 -20 \ — i
Page 135: m I s 1 \\ I , t Frequency (GHz) Fi
Page 139 and 140: D - The propagation margin is then
Page 141 and 142: 1- * w -180 -190 -m -21 / ---+---4~
Page 143 and 144: - . . 6.9 UPLINK NOISE IN SATELLITE
Page 145 and 146: 280 260 240 220 200 180 160 140 120
Page 147 and 148: 6.10 REFERENCES Ahmed, I.Y. and L.J
Page 149 and 150: ● International Telecommunication
Page 151 and 152: Atmospheric Emission observations,
Page 153 and 154: 8.6 and 3.2 mm Radio Waves by Cloud
Page 155 and 156: I Strickland, J.I. (1974), “Radar
Page 157: D Wulfsberg, K.N. (1964), “Appare
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