When working with RF circuits, engineers face a unique challenge. Between the transceiver or modem and the antenna, electrical signals are conducted at ultra high frequencies, beyond thousands of hertz. The result of this is that as signals move between components (e.g. from the transceiver to a PCB trace, from a PCB trace to the antenna), if the components have different impedances, a reflection of the AC wave occurs, creating destructive interference and reducing the power of the overall wave (similar to how a light wave might experience some reflection as it travels through two different media, such as air to water).

This destructive interference takes away from the total transmit power of the RF circuit, and when you're 400km away from your ground station, every bit counts. As such, RF board designers must make sure they try to match the impedance of all of their components as best they can. This can involve widening PCB traces and selecting antennas and transceivers with similar impedances. If any impedance mismatch does occur, it must be accounted for in a link budget.

Note that impedance mismatch occurs in all circuits, but simply becomes more prevalent in high frequency ones.