Beam Riding - Radar Beam Riding

Radar Beam Riding

Beam riding is one of the simplest methods of missile guidance using a radar. It was widely used for surface-to-air missiles in the post-World War II era for this reason.

Early tracking radars generally use a beam a few degrees wide, which makes it easy to find the target as it moves about. These radars are normally used in conjunction with wide-scanning early warning radar systems, although in modern systems the two functions can be combined. When a target is detected, some radars had the ability to "lock on", and track the target automatically.

Beam riding systems can be easily adapted to work with such a system. By placing receiver antennas on the rear of the missile, the onboard electronics can compare the strength of the signal from different points on the missile body and use this to create a control signal to steer it back into the center of the beam. In practice, the systems used additional information from the signal, such as conical scanning, to more accurately calculate the centerline. With this simple system, the majority of the tracking problem is offloaded from the missile to the launching platform. In early examples, these were ground-based radars with all the equipment necessary for tracking.

The inherent disadvantage of the radar beam riding system is that the beam spreads as it travels outward from the broadcaster. As the missile flies towards the target, it therefore becomes increasingly inaccurate. This is not a problem at short ranges, but as many early surface-to-air missiles were designed to work at long ranges, this was a major issue. For example, earlier versions of the RIM-2 Terrier missile introduced in the 1950s were beam riders, but later variants employed semi-active radar homing to improve their effectiveness against high-performance and low-flying targets. In contrast to beam riding, semi-active guidance becomes more accurate as the missile approaches the target.

Another issue is the guidance path of the missile is essentially a straight line to the target. This is useful for missiles with a great speed advantage over their target, or where flight times are short, but for long-range engagements against high-performance targets the missile will need to "lead" the target in order to arrive with enough energy to do terminal manoeuvres. A possible solution for this problem was to use two radars, one for tracking the target and another for guiding the missile, but this drove up implementation costs. A more common solution for long-range missiles was to guide the missile entirely independently of the radar, using command guidance, as was the case for the Nike Hercules. Pure radar beam riding was rare by 1960.