Editing AIM-7 Sparrow (section)

==Principle of guidance ==

[[File:Test Set, Computer, AN APM-282.jpg|thumb|Close-up of an AN/APM-282 test set computer, for testing AIM-7 missile guidance]]
The launching aircraft illuminates the target with its radar. In 1950s radars, these were single-target tracking devices using a [[Nutation|nutating]] horn as part of the antenna, thereby sweeping the beam in a small cone. Signal processing is applied to determine the direction of maximum illumination, thereby developing a signal to steer the antenna toward the target. The missile detects the reflected signal from the target with a high-gain antenna in a similar fashion and steers the entire missile toward closure with the target. The missile guidance also samples a portion of the illuminating signal via rearward-pointing [[waveguide]]s. The comparison of these two signals enabled logic circuits to determine the true target reflection signal, even if the target were to eject radar-reflecting [[chaff (radar countermeasure)|chaff]].