Transmitter Models

Complex Transmitter Model

The Complex Transmitter model allows you to select among a variety of analytical and realistic antenna models, and to define the characteristics of the selected antenna type. The following parameters can be set for this model:

Model Specs

Frequency. The RF carrier frequency of the transmitter.

Power. The RF power output of the transmitter as measured at the input to the antenna.

Data Rate. The transmitter's data rate is a compound dimension with data bits and time as simple dimensions. For example, a data rate entered as 2.5 kb/msec will be converted to 2.5 megabits per second data rate. Valid data bit units are bits (b), kilobits (kb), megabits (mb), gigabits (gb), and terabits (tb). Valid time units are seconds (sec), milliseconds (msec), microseconds (usec), nanoseconds (nsec), and picoseconds (psec). Changing the transmitter’s data rate could affect the values of the Modulator.

Antenna

You can select to embed an antenna model from the Component Browser or you can link to an antenna object. Antenna objects are listed in the Object Browser.

To embed an antenna model, select Embed as the Reference Type. On the Model Specs subtab, click the Antenna Models ellipsis button to select an antenna model. You can define polarization and orientation parameters for an embedded antenna using the Polarization and Orientation subtabs. For parameter definitions, see Antenna Orientation Methods and Polarization.

To link to an antenna object, select Linked as the reference type and select the antenna from the drop-down list. You can define polarization parameters for a linked antenna. For parameter definitions, see Polarization. You cannot modify the antenna's model specification and orientation parameters while in the receiver's basic properties. To modify these parameters, go to the antenna's basic properties.

If a transmitter or receiver is using a linked antenna, the geometric and vector constraints are not available for that transmitter or receiver because STK pulls the geometric and vector constraints from the antenna.

For information on antenna types and parameters, and how to link to an antenna on a sensor, see STK Antenna Models.

  • A linked antenna is the focus of the communications link, which means that all geometry and vector computations are carried out on the linked antenna instead of on the receiver to which that antenna is linked.
  • The reference type is only available for transmitters, receivers, and radar objects that are not a child of a Sensor object. If one of these objects is a child to a Sensor, the only option is to use the embedded antenna model. For more information, see Linking to an Antenna that Resides on a Sensor.

Polarization for Complex UAN Format and Complex ANSYS *.ffd Format antenna models is pulled from the external file that you added to the Antenna's Model Specs tab. Select Use on the Antenna's Polarization tab to enable the polarization specified in the file. You can ignore the remaining options on the polarization tab as they do not apply to these antenna models.

Modulator

STK Communications allows you to select from multiple modulators, including user-defined modulators. Each modulator has a defined modulation. The modulation determines two characteristics:

  1. The fraction of transmitter power contained within the receiver’s bandwidth (computed in the Bandwidth Overlap Factor).
  2. The translation between the signal-to-noise ratio (Eb/No) and the resulting bit error rate (BER). The BER curves used in STK represent theoretical performance curves. When modeling real demodulators, you may want to use an external modulation type with a slightly degraded BER curve. Typical systems run within 1-2 dB of the theoretical values at a given bit error rate. Perfect bit synchronization is assumed when demodulating the data to get a BER.

STK Modulators can be separated into five general categories: Common Analytical Modulators, Jammer/Interference Modulators, Coded Modulators, External File Modulators, and Script Plugin Modulators.

For more information on modulators, see one of the following categories:

Filter

To specify a filter model, select Use and browse to a filter model. For more information, see Filter Models.

Additional gains and losses

During communications analyses, it is often necessary to model gains and losses that affect performance but are not defined using built-in analytical models. STK enables you to model these by specifying miscellaneous gains and losses to add to the equation.

Post Transmit Gains/Losses. To define a Gain or Loss, click Add. Enter a brief description of the Gain or Loss in the Identifier field and its value in the Gain field. Remember to make it negative if you are entering a Loss. Once you enter the values, you can click Remove to delete an entry from the table. To change an existing entry, simply edit the fields in the grid. The value in the Pre-Receive field will reflect the net value of all gains and losses recorded in the table.