The system temperature interface allows you to specify the system's inherent noise characteristics. These can help simulate real-world RF situations more accurately. Radars and all Communications receiver models except simple allow you to define how you want the system temperature to be calculated. Simple model communications receivers do not need this since the system noise temperature is included in the g/T value that you specify. The Definition page for a communications receiver and the System page for a radar contain the following System Temperature frame:
You can set System Temperature by selecting the Constant option and entering a value directly. Alternatively, you can have STK calculate the system temperature for you. To do so, select the Calculate option and click Details..., bringing up the System Temperature window. This window allows you to specify the parameters that STK will use in calculating system temperature:
System temperature parameters
| Parameter | Description |
|---|---|
| Receiver Noise Figure | The noise figure represents the contribution to the total system noise by the gain stages of the receiver. It can be thought of as a factor that describes the noise level in a receiver relative to that in a theoretically perfect receiver. The noise figure is always greater than 0 dB. |
| Transmission Line Loss | The loss of the transmission line between the antenna and receiver. |
| Transmission Line Temp | The physical temperature of the receiver transmission line. |
| Antenna Noise | Noise that the antenna picks up from radiating bodies within its radiation pattern - a function of the direction in which the antenna is pointing, its radiation pattern and the state of the surrounding environment. The following options are available:
In addition, you can select an external antenna noise file. Click the ellipsis () button to browse for the file name. The file allows you to specify the antenna noise temperature as a function of the ground elevation angle. In addition, you can opt to take Sun and/or Rain noise into account. The Rain, Atmosphere, and external noise options are available only for facilities and targets, while Cosmic Background noise is available only for vehicles. Earth noise is always included in the calculation for facilities and targets. |
| Earth Temperature | If you select Calculated and Earth under Antenna Noise, you can optionally set the Earth temperature at the local receiver/radar level. To set the Earth temperature, clear Inherit from Scenario and enter a new value. The default value is 290 degrees Kelvin, which is the Earth's blackbody radiation temperature. |
See Maral, G. and M. Bousquet, Satellite Communications Systems: Systems, Techniques and Technology, 2nd ed., Chichester: Wiley (1993), p. 29.
If you select the Constant option for Antenna Noise, the read-only Calculated System Temp field at the bottom of the System Temperature window displays the results of the most recent calculation of system temperature. Those results are also displayed in the System Temperature field when you click OK to return to the Definition page for the communications receiver or the System page for the radar.
The External, Intelsat and GIMROC antenna patterns are nonanalytic in nature and, therefore, the use of integrated antenna gain is not recommended for these antenna types.
For the effect of antenna polarization on system and antenna noise temperature, see the Technical Notes.