Recommendation itu-r p. 838-2 Specific attenuation model for rain for use in prediction methods




Yüklə 91.87 Kb.
tarix14.04.2016
ölçüsü91.87 Kb.

Rec. ITU-R P.838-2

RECOMMENDATION ITU-R P.838-2

Specific attenuation model for rain for use in prediction methods

(Question ITU-R 201/3)

(1992-1999-2003)

The ITU Radiocommunication Assembly,



considering

a) that there is a need to calculate the attenuation due to rain from a knowledge of rain rates,



recommends

1 that the following procedure be used.

Specific attenuation R (dB/km) is obtained from the rain rate R (mm/h) using the power law relationship:



(1)

The frequency-dependent coefficients k and  are given in Table 1 for linear polarizations (horizontal: H, vertical: V) and horizontal paths.

The values in Table 1 have been tested and found to be sufficiently accurate for attenuation prediction up to frequencies of 55 GHz.

The coefficients k and  may alternatively be determined, as a function of frequency, from the following equations, which have been derived from curve-fitting to power-law coefficients derived from scattering calculations:

(2)

(3)

where:

f : frequency (GHz)

k : either kH or kV

 : either H or V.

TABLE 1


Frequency dependent coefficients for estimating specific
attenuation using equations (4), (5) and (1)



Frequency
(GHz)


kH

kV

H

V

1

0.0000387

0.0000352

0.9122

0.8801

1.5

0.0000868

0.0000784

0.9341

0.8905

2

0.0001543

0.0001388

0.9629

0.9230

2.5

0.0002416

0.0002169

0.9873

0.9594

3

0.0003504

0.0003145

1.0185

0.9927

4

0.0006479

0.0005807

1.1212

1.0749

5

0.001103

0.0009829

1.2338

1.1805

6

0.001813

0.001603

1.3068

1.2662

7

0.002915

0.002560

1.3334

1.3086

8

0.004567

0.003996

1.3275

1.3129

9

0.006916

0.006056

1.3044

1.2937

10

0.01006

0.008853

1.2747

1.2636

12

0.01882

0.01680

1.2168

1.1994

15

0.03689

0.03362

1.1549

1.1275

20

0.07504

0.06898

1.0995

1.0663

25

0.1237

0.1125

1.0604

1.0308

30

0.1864

0.1673

1.0202

0.9974

35

0.2632

0.2341

0.9789

0.9630

40

0.3504

0.3104

0.9394

0.9293

45

0.4426

0.3922

0.9040

0.8981

50

0.5346

0.4755

0.8735

0.8705

60

0.7039

0.6347

0.8266

0.8263

70

0.8440

0.7735

0.7943

0.7948

80

0.9552

0.8888

0.7719

0.7723

90

1.0432

0.9832

0.7557

0.7558

100

1.1142

1.0603

0.7434

0.7434

120

1.2218

1.1766

0.7255

0.7257

150

1.3293

1.2886

0.7080

0.7091

200

1.4126

1.3764

0.6930

0.6948

300

1.3737

1.3665

0.6862

0.6869

400

1.3163

1.3059

0.6840

0.6849

The remaining coefficients are given in Tables 2 and 3.

TABLE 2

Coefficients in equations (2) and (3) for horizontal polarization





a

b

c

mk

ck

m

c

j  1

0.3364

1.1274

0.2916

1.9925

–4.4123





2

0.7520

1.6644

0.5175

3

–0.9466

2.8496

0.4315

i  1

0.5564

0.7741

0.4011





–0.08016

0.8993

2

0.2237

1.4023

0.3475

3

–0.1961

0.5769

0.2372

4

–0.02219

2.2959

0.2801

TABLE 3


Coefficients in equations (2) and (3) for vertical polarization





a

b

c

mk

ck

m

c

j  1

0.3023

1.1402

0.2826

1.9710

–4.4535





2

0.7790

1.6723

0.5694

3

–1.0022

2.9400

0.4823

i  1

0.5463

0.8017

0.3657





–0.07059

0.8756

2

0.2158

1.4080

0.3636

3

–0.1693

0.6353

0.2155

4

–0.01895

2.3105

0.2938

For linear and circular polarization, and for all path geometries, the coefficients in equation (1) can be calculated from the values in Table 1 using the following equations:

(4)

(5)

where  is the path elevation angle and  is the polarization tilt angle relative to the horizontal (  45 for circular polarization).

For convenience, a quick estimate of values of k and  at frequencies other than those in Table 1, can be obtained from Figs. 1 to 4.











Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©azrefs.org 2016
rəhbərliyinə müraciət

    Ana səhifə