Medium Retransmitter Model

The Medium Retransmitter provides more flexibility by letting you specify gain and saturated output power separately instead of entering saturated EIRP directly, as in the Simple model. The Medium Retransmitter model uses an isotropic, omnidirectional antenna, which is an ideal spherical pattern antenna with constant gain. You can set the following parameters for the Medium model:

Model specs

Sat. Power. Saturated Power is the RF Power output of the transmitter as measured at the input to the antenna when the amplifier is at its saturated state.

Gain. This is the transmitter antenna's isotropic gain.

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

Use. 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.