The Patriot Missile Launcher system is the USA base defence structure in Command and Conquer: Generals. Their tooltip says;
Detect enemy stealth units, can relay enemy position to nearby Patriots
This means that if you build multiple Patriot Missile Launchers in close vicinity to each other, they will relay the position of enemies allowing launchers that may be out of range of attack to still fire at an incoming enemy once it has been detected by another Patriot Missile Launcher.
How close do I have to place the Patriot Missile Launchers to each other in order to qualify as 'nearby'?