ITU-R P.838-3 用于预测方法的降雨特定衰减模型

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Rec. ITU-R P.838-3 1

RECOMMENDATION ITU-R P.838-3

Specific attenuation model for rain for use in prediction methods

(Question ITU-R 201/3)

(1992-1999-2003-2005)

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.

The specific attenuation γR (dB/km) is obtained from the rain rate R (mm/h) using the power-law

relationship:

=γ kR

R (1)

Values for the coefficients k and α are determined as functions of frequency, f (GHz), in the range

from 1 to 1 000 GHz, from the following equations, which have been developed from curve-fitting

to power-law coefficients derived from scattering calculations:

∑























−

−=

10 log

log

explog

jcfm

ak (2)

∑

αα ++























−

−=α

10 log

log

exp

jcfm

a (3)

where:

: frequency (GHz)

k : either kH or kV

α : either αH or αV.

Values for the constants for the coefficient kH for horizontal polarization are given in Table 1 and

for the coefficient kV for vertical polarization in Table 2. Table 3 gives the values for the constants

for the coefficient αH for horizontal polarization, and Table 4 gives the values for the constants for

the coefficient αV for vertical polarization.

2 Rec. ITU-R P.838-3

TABLE 1

Coefficients for kH

j aj bj cj mk ck

1 –5.33980 –0.10008 1.13098

2 –0.35351 1.26970 0.45400

3 –0.23789 0.86036 0.15354

4 –0.94158 0.64552 0.16817

–0.18961 0.71147

TABLE 2

Coefficients for kV

j aj bj cj mk ck

1 –3.80595 0.56934 0.81061

2 –3.44965 –0.22911 0.51059

3 –0.39902 0.73042 0.11899

4 0.50167 1.07319 0.27195

–0.16398 0.63297

TABLE 3

Coefficients for αH

j aj bj cj mα cα

1 –0.14318 1.82442 –0.55187

2 0.29591 0.77564 0.19822

3 0.32177 0.63773 0.13164

4 –5.37610 –0.96230 1.47828

5 16.1721 –3.29980 3.43990

0.67849 –1.95537

TABLE 4

Coefficients for αV

j aj bj cj mα cα

1 –0.07771 2.33840 –0.76284

2 0.56727 0.95545 0.54039

3 –0.20238 1.14520 0.26809

4 –48.2991 0.791669 0.116226

5 48.5833 0.791459 0.116479

–0.053739 0.83433

Rec. ITU-R P.838-3 3

For linear and circular polarization, and for all path geometries, the coefficients in equation (1) can

be calculated from the values given by equations (2) and (3) using the following equations:

2/]2coscos)([ 2τθ−++= VHVH kkkkk (4)

()

kkkkk VVHHVVHH 2/]2coscos–[ 2τθαα+α+α=α (5)

where θ is the path elevation angle and τ is the polarization tilt angle relative to the horizontal

(τ = 45° for circular polarization).

For quick reference, the coefficients k and α are shown graphically in Figs. 1 to 4, and Table 5 lists

numerical values for the coefficients at given frequencies.

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摘要：

ITU-R P.838-3 是国际电信联盟无线电通信部门（ITU-R）发布的一项技术标准，专门用于预测无线电波在降雨环境下的特定衰减（Specific Attenuation）。该模型通过经验公式，基于降雨强度、频率和极化方式，提供对电磁波在雨滴中传播时衰减率的精确估算，广泛应用于卫星通信、地面微波链路以及雷达系统的链路预算和可靠性分析。文档详细定义了计算系数（如k和α）的方法，覆盖频率范围从1 GHz到1,000 GHz，并考虑了不同极化下的衰减差异。对于从事无线通信工程、洪水预警雷达设计或气

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