Multibeam antennas are designed to model small- to medium-sized STK arrays of antenna elements, called beams, on an antenna. Each beam is modeled as an independent antenna with its own gain pattern type, frequency, polarization, orientation, and offset from the body coordinate frame of the antenna's parent transmitter/receiver object.
Note the following considerations when modeling scenarios with multibeam antennas:
- A multibeam model may have only one beam and is like a complex transmitter/receiver model, which supports only one antenna. Complex models are recommended for systems with one antenna or shared antennas.
- A multibeam antenna with more than one beam uses the beam selection strategy to select one beam for link budget computations. The selection strategy may call for a different beam at each time step.
- Each selected beam imposes its frequency gain, polarization, orientation, and offset during link budget computations.
- The 2D and 3D antenna graphics display all the active beams in the array simultaneously.
- The Aggregate All Active Beams option combines the gain and EIRP into one composite beam. The composite beam is created with the following assumptions:
- All beams have the same phase (zero).
- The beam orientation and offset is used to compute the contribution of each beam to the composite Gain and EIRP.
- Each beam's polarization is not used when computing the aggregate beam.
The multi-beam antenna does not use the beam positional offset when computing propagation loss.
Computing Line of Sight (LOS) Visibilities
Access computes the object's Line of Sight (LOS) visibilities between the multibeam antenna's parent objects. The beam level offsets and orientation are not used to compute LOS visibilities. These offsets are expected to be from a millimeter to a maximum of a few meters and offer a very small impact on the LOS visibilities between objects with a range of several kilometers to thousands of kilometers.
When the Aggregate All Active Beams option is selected, the link budget graphics and LOS visibilities are computed from the parent body coordinates frame origin. If you want to add an offset for the entire multibeam antenna, it is recommended that you attach the multibeam transmitter/receiver to a sensor and add the offset to the sensor object.
STK offers complete flexibility in placing the individual beams on the parent coordinate frame. No bounds are imposed on the offset values entered for each beam, and no messages are issued. STK allows you to enter extreme values (e.g., several thousands of kilometers) and attempts to use these values for link budgets and 2D and 3D graphics. The Access LOS computations are still initiated from the parent objects and may have significant differences. This is in contrast to the antenna objects and the complex transmitter/receiver models. It is strongly suggested that you use complex models when access LOS is strictly required from the antenna position.