🌧️ Rain Attenuation Calculator

ITU-R P.838 specific attenuation + P.618 slant-path rain fade vs availability

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Link & Site

Rain

Results

Specific attenuation γ_R
– dB/km
Effective path length
– km
Attenuation A₀.₀₁
– dB
Rain fade @ target
– dB
Sky-noise rise ΔT
– K
Outage time / year
–
Rain fade vs link availability
AvailabilityOutage % (p)Rain fade (dB)
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📖 How to use

  1. Enter frequency, elevation and polarization; pick a preset band if unsure.输入频率、仰角和极化;不确定就先选预设频段。
  2. Set the local rain rate R₀.₀₁ (from ITU-R P.837), station latitude, height and rain height.设置当地降雨率 R₀.₀₁(查 ITU-R P.837)、站点纬度、海拔和雨高。
  3. Choose your target availability (e.g. 99.99%).选择目标可用度(如 99.99%)。
  4. Read the rain fade (dB) at that availability, plus the fade-vs-availability table.读取该可用度下的雨衰(dB),以及"雨衰-可用度"对照表。
  5. Add the fade as the "Rain loss" term in your link budget.把该雨衰作为链路预算里的 "Rain loss" 项加入。
  6. Arrived via the ↗ link next to the Link Budget's rain-loss field? Click the return bar at the top to carry the fade straight back (the bar never appears on a direct visit).如果是点链路预算雨衰字段旁的 ↗ 链接跳转而来,点顶部的返回条即可把雨衰直接带回(直接访问不会显示返回条)。
  7. For a downlink, note the Sky-noise rise ΔT — the same fade also heats the receive noise temperature; enable Rain sky-noise coupling in the link budget to include that second hit.下行链路注意天空噪声抬升 ΔT——同一场雨还会抬升接收噪温;在链路预算里开启雨致天空噪声耦合即可把这部分损失一并计入。

About this rain attenuation model

This tool implements the standard ITU-R P.838-3 (specific rain attenuation coefficients k and α) combined with the ITU-R P.618-13 slant-path prediction method, including the horizontal and vertical path-reduction factors and the availability scaling.

Specific attenuation: γ_R = k · Rα (dB/km), where k and α depend on frequency, polarization and elevation angle.

The attenuation exceeded 0.01% of the year, A₀.₀₁ = γ_R · L_E, is then scaled to your target availability. Rain fade rises sharply with frequency — negligible at C-band, significant at Ku, and a dominant design driver at Ka-band and above.

For accurate site numbers, use the local R₀.₀₁ rain rate from ITU-R P.837 and rain height from ITU-R P.839. Feed the resulting fade into the link budget calculator as your rain-loss term. All computation runs locally in your browser.

关于本雨衰模型

本工具实现标准的 ITU-R P.838-3(降雨比衰减系数 k 与 α),并结合 ITU-R P.618-13 斜路径预测方法,包含水平与垂直路径缩减因子以及可用度换算。

比衰减: γ_R = k · Rα(dB/km),其中 k 与 α 取决于频率、极化和仰角。

一年中 0.01% 时间被超过的衰减 A₀.₀₁ = γ_R · L_E 随后被换算到你的目标可用度。雨衰随频率急剧上升——在 C 波段可忽略,在 Ku 波段显著,到 Ka 波段及以上成为主导设计因素。

要得到准确的站点数值,请使用来自 ITU-R P.837 的当地 R₀.₀₁ 降雨率和来自 ITU-R P.839 的雨高。把得到的雨衰作为雨衰损耗项填进链路预算计算器。全部计算在你的浏览器本地完成。