The AN/MPQ-65 radar
A C-band phased array on a trailer, 5,000+ elements, beam-steering in microseconds. Search, track and missile-guidance commands all share the same antenna. Range against fighter-sized targets is 100+ km; against ballistic missiles, less.
TVM guidance
Track-Via-Missile: the missile has a seeker but no autopilot brain. It relays what it sees to the ground radar, which computes corrections and uplinks them. PAC-3 added hit-to-kill — no warhead, just kinetic energy.
Combat record
1991: PAC-2 vs. Scud — disputed; original 96% kill claim later revised down to under 50%. 2003: friendly-fire incidents shooting down a Tornado and an F/A-18. 2014–2023: Saudi PAC-3s vs. Houthi missiles — mixed. 2022+: Ukrainian PAC-3 intercepts of Russian Kinzhal and ballistic missiles — strong public record.
Why it's hard
A ballistic missile re-enters at Mach 5+. The radar has seconds. Decoys, manoeuvring warheads, GPS-jammed engagements — every intercept is a near-miracle of timing. Patriot is good; it isn't magic.