Galileo 'side lobe' signals

Navigation satellites – such as Europe's Galileo, the US GPS, Russia’s Glonass or their Japanese, Chinese and Indian counterparts – aim their antennas directly at Earth. Any satellite orbiting above these constellation can only hope to detect signals from over Earth’s far side, but the majority are blocked by the planet. For a position fix, a satnav receiver requires a minimum of four satellites to be visible, but this is most of the time not possible if based solely on front-facing signals. Instead, satnav receivers in higher orbits can make use of signals emitted sideways from navigation antennas, within what is known as ‘side lobes’. Just like a flashlight, radio antennas shine energy to the side as well as directly forward.