ITU-R P618-12 Rain Model
This ITU rain model is included for backward compatibility and is superseded by ITU-R P618-13. This tropospheric scintillation model supersedes previous version
| Parameter | Description |
|---|---|
| Surface Temperature | Enter a surface temperature for the model to use. |
| Enable Cross Polarization Loss |
If you select this check box, the model will include the effect of depolarization of a communications link due to rain. This option is available only for releases 10, 12, and 13 of the P618 model. |
Tropospheric Scintillation
| Parameter | Description |
|---|---|
| Surface Temperature | Enter the surface temperature value. |
| Tropo Fade Outage | Enter the Tropospheric Fade Outage as a percentage. STK computes the loss in dB that occurs for the percentage time not exceeding the specified limit. |
| Percent Time Refractivity Gradient < -100 N | The percentage of time that the reflectivity gradient in the lowest 100 meters of the atmosphere is less than -100 N units/km. |
| Fade depths for the average year | Computes the fade depth exceeded for a percentage of time over an average year. For example, fade depth exceeds the computed value for the climate of an average year as a percentage of the time over the year. |
| Fade depths for the average annual worst month | Computes the fade depth exceeded for a percentage of time for the month with the worst climate over a year. Fade depth exceeds the computed value for a percentage of time over the worst month of the year. |
The Tropospheric Scintillation model is based on modeling RF energy in a beam with a certain beam width. Since Dipole antennas are omni-directional and do not provide a beam width, a standard dish antenna with 1.0 meter diameter and 70% efficiency is assumed for computing scintillation loss only. This does not impact link budget computations, which are still carried out for a dipole antenna selected as the system model.
As of STK 12.7, the model decides whether to calculate deep fade or shallow fade depending on the link elevation angle. In previous versions of STK, you could select a Compute Deep Fade check box to force a deep fade calculation. For older scenarios with this check box selected, STK 12.7 and later will ignore this selection.