System Noise Temperature

The Receiver's System Noise Temperature enables you to specify the system's inherent noise characteristics. These can help simulate real-world RF situations more accurately. All receiver models except simple enable you to define how you want STK to calculate the system temperature. Simple model receivers do not need this since STK includes the system noise temperature in the g/T value that you specify.

For Medium, Complex, and Multibeam antennas, to completely specify the total system noise, you must also specify gains and losses on the Model Specs tab. These gains and losses are due to the low noise amplifier (LNA) and the cabling that connects it to the antenna and to the receiver front end.

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.
  • 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 Enter 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 Enter the physical temperature of the low-noise amplifier (LNA).
LNA to Receiver Transmission Line Temperature Enter the physical temperature of the transmission line between the LNA and the receiver.
Antenna Noise This is noise that the antenna picks up from radiating bodies within its radiation pattern. It is 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.

    Also, you can select an external antenna noise file. Click the ellipsis button to browse for the file name. Add this file to specify the antenna noise temperature as a function of the ground elevation angle. With this file, you can opt to take Sun and/or Rain noise into account.

    The 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 have the option to set the Earth temperature at the local receiver level. To set the Earth temperature, clear the Inherit from Scenario check box and enter a new value. The default value is 290 degrees Kelvin, which is the Earth's blackbody radiation temperature.
User-supplied plugin The plugin is provided with the dynamic STK object data, such as position, velocity, and attitude information. The plugin may compute a noise temperature value. This external noise temperature is added to the antenna's external noise and used in link budget or radar performance computations.

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, thus, 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.