Satellite Communications (SATCOM) Practice Test

Polarization multiplexing uses two orthogonal polarization states to carry separate data streams, which increases potential capacity, but the two channels share the same propagation path. Because of imperfections in antennas, feed networks, and the surrounding environment, energy from one polarization can leak into the other. If that leakage is not kept very low, crosstalk occurs, degrading the signal quality and eroding the benefits of multiplexing. Therefore, the design must ensure cross-polar isolation is high enough to minimize leakage and preserve the integrity of both channels. The other ideas don’t fit as well. Polarization multiplexing isn’t limited to downlink, since uplink can also use dual polarization with proper isolation. The transmitter doesn’t necessarily require two separate physical feeds—the system can use a single dual-polarized feed or a polarizing network to generate the two polarizations. And the capacity gain isn’t guaranteed to double regardless of isolation; if isolation is poor, interference dominates and the realized capacity gain drops accordingly.