With beam riding the fire control system keeps a narrow radar or laser beam aimed exactly at the target. The missile looks backwards, at the beam itself, and measures how far it is from the centre of the beam. Its only task: stay in the centre of the beam. If the target is in the beam and the missile stays in it, they come together by themselves.
Properties:
- Simple, cheap missile: no seeker, only a rearward-facing beam receiver. Several missiles can fly in the same beam.
- Almost impossible to jam from the target: the control link (the beam) points from the platform towards the target; with laser beam riding the signal at the target is moreover very weak and hard to detect — popular with modern short-range air defence and anti-tank weapons.
- Accuracy decreases with range: the beam gets wider (Angular resolution), so the missile "may" drift further from the ideal line the further away the target is. Only suitable for short to medium range.
- The platform is tied down: the director has to keep the target in the beam until impact — no "fire and forget", and the platform betrays its activity (in radar beam riding).
- Energetically inefficient against crossing targets: the missile follows the rotating line of sight instead of leading the target.