Principle of Guidance (semi-active Version)
The launching aircraft will illuminate the target with its radar. In radars of the 1950s these were single target tracking devices using a nutating horn as part of the antenna. This caused the beam to be swept in a small cone. Signal processing would be applied to determine the direction of maximum illumination and so develop 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 waveguides. 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.
Read more about this topic: AIM-7 Sparrow
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