Simple Retransmitter Model
The Simple Retransmitter model is convenient when you do not have all the information necessary to model the transmitter in detail, for example, during the system engineering process. The Simple Retransmitter model uses an isotropic, omnidirectional antenna, which is an ideal spherical pattern antenna with constant gain. You can set the following parameters for this model:
Model specs
Sat. EIRP. Saturated EIRP is the Effective Isotropic Radiated Power at the output of the transmit antenna.
Sat. Flux Density. Saturated Flux Density is the amplifier's saturation point by the input flux density in dBW/m2. This represents the per carrier flux density for systems supporting multiple carriers per transmitter.
Operational Mode. Choose one of the following modes of operation:
- Use unadjusted receive flux density.
This mode is generally used by fixed-geometry communication links (such as GEO satellites and ground stations). The satellite retransmitter's saturated flux density is usually read from the flux density and/or g/T contours. The saturated flux density inherently contains the appropriate receiver gain within the value used in the link analysis and does not change over time.
- Use receiver antenna gain delta adjusted flux density.
This model is suitable for modeling bent-pipe transponders with time-dynamic communication links. The positions of the user terminal transmitters and receivers may be rapidly changing. This necessitates adjustment of the incoming flux density by the receiver's delta gain (maximum gain - current gain) and accounts for the loss of signal power due to the link direction of the satellite's receiver.
- Use constant output power.
This mode models the retransmitter with automatic gain control (AGC) circuitry. The power amplifier output is maintained at the optimum operating power level. This power output level is held constant independently of the input flux density. The AGC dynamic range is assumed to be enough to cover the amplifier's operating power levels.
Polarization. To specify a polarization model, select Use and select a polarization type. For descriptions of the polarization parameters, see Polarization.
Transfer functions
For information on defining a frequency, power backoff, or carrier to intermod (C/Im) ratio coefficient, see Transfer Functions.
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.