System Noise Temperature

The Receiver's System Noise Temperature allows you to specify the system's inherent noise characteristics. These can help simulate real-world RF situations more accurately. All receiver models except simple allow you to define how you want the system temperature to be calculated. Simple model receivers do not need this since the system noise temperature is included in the g/T value that you specify. The Receiver's System Noise Temperature tab contains the following System Temperature options:

You can set System Temperature by selecting Constant and entering a value directly.
Alternatively, you can have STK compute the system temperature for you. Select Compute and specify the following parameters that STK will use in calculating system temperature.

Parameter	Description
Antenna to LNA Transmission Line Temperature	The physical temperature of the transmission line between the antenna and the LNA.
LNA 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.
LNA Temperature	The physical temperature of the low noise amplifier (LNA).
LNA to Receiver Transmission Line Temperature	The physical temperature of the transmission line between the LNA and the receiver.
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: Constant - Enter the desired value. Compute - Select whether to use Earth, Sun, Atmosphere, Urban Terrestrial, Rain, Clouds & Fog, Tropo Scintillation, and/or Cosmic Background noise in the calculation. You can also enter a constant value for Other Sources. 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 Compute and Earth under Antenna Noise, you can optionally set the Earth temperature at the local receiver 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.

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.