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Source: List of Beam approach beacon system units

This is a List of Beam Approach beacon system Units of the Royal Air Force.
The first system to guide RAF aircraft safely down onto a runway was called the Standard Blind Approach (SBA) system and was trialled in the late 1930s. It was also being used by a few civil airports. By late 1941 the word 'Blind' was changed to 'Beam' as it was felt that blind did not give a reassuring feel to a system used when visibility was very low. The word Standard came from Standard Radio, the name of the company that made the equipment under license from the German company that designed it. However the equipment was also 'standard' fit on RAF aircraft. The change from Blind to Beam is evidenced in the two sets of Unit names in the tables below.
There were no physical beams in the system at all, rather it relied on a heavily distorted dipole radiation pattern using a single transmitter. Instead of 'beams' it used a single heavily distorted toroid that was flipped left and right with a periodicity that simulated a morse code letter, the plane of equal field strength in this arrangement being mathematically equal to a line of zero width - a perfect 'beam' from an imperfect, cheaper, and simple radio transmitter. SBA was not automatic, the pilot flew the aircraft at all times.
The Beam Approach Beacon System (BABS) is an automatic radar landing system developed in the early 1940s but not used until much later when it replaced the SBA system.