Two-Ray Atmospheric Model

This propagation model applies to short-range and low antenna heights for the transmitter and the receiver antennas. For more information, see Two-Ray Model.

You can apply the model to transmitters and receivers on any central body, as long as both terminals are on the same central body surface and satisfy the basic conditions of low antenna heights and short distances.

STK does not restrict range or the transmitter and receiver's heights above terrain. The best practice is to limit the range to a few tens of kilometers and heights to a few hundred meters.

Model geometry is based on the flat plane ground surface. Current implementation does not account for the antenna gain towards direct rays or the ground reflected ray directions.

This is not an irregular terrain model. It only uses height above ground.

The scenario central body may be different from the central body of the objects. Take care to configure the position and altitude of the objects with respect to their correct central body.

Jake WC. Microwave Mobile Communications. IEEE Press
Rapport TS. Wireless Communications Principal & Practice (2nd ed). ISBN 978-0130422323
Wikipedia: Two-ray ground reflection model

Loss Factor

Loss Factor is a discretionary multiplier that you can use to make adjustments for additional conditions in the link path that STK isn't already accounting for. For example, if you know that the path has thick vegetation that will result in more loss, you can use the loss factor to help account for it. Valid values for the loss factor in STK range from 0.1 to 10.0, and the default value is 1.0.

Note that this is just a multiplicative factor. The application will adjust the loss (gain) values higher or lower. If you plot the loss curve vs range, you will see the whole curve move up or down.