Sir Robert Watson-Watt
By Illa Vij

IN July 1940, when the Battle of Britain started, about 50 radar stations were operating. The electronic net of aircraft detectors stretched from the Shetland Islands to Dover, along the South coast to Cornwall and up to Wales. In August when the battle was at its peak, numerous German aircraft were destroyed. No air power could suffer such a loss for long and on September 17, Hitler took a decision that changed the course of History.

The radar was developed during the years preceding World War II by a British team led by Sir Robert Watson-Watt. Radar is an acronym for Radio Detection and Ranging. It is a method of finding the location of an object in space by bombarding it with electro-magnetic waves and then measuring the time that it takes for such waves to return to the sender. Watson did not find the principle that lay behind the making of radar, but his genius lay in the fact that he alone saw the possibilities and worked out a device to put the available components and forces into working — to make the radar.

While working on a system in which aviators could be warned of the approaching thunderstorms, he adopted the use of cathode-rays tube (today used as a picture tube in televisions) He used the tube as a direction finder, but could not gain the much-required accuracy. In 1930, Baron Von Ardenne presented him with a tube that was more sensitive and more powerful. In 1932, something unusual happened. He noticed that as a passing aircraft moved overhead, signals in the form of broken luminous lines formed in the tube. Such an incident had taken place before too and that made Watson realise that the tube could be further worked upon to use it for the detection of aircraft flying within a certain range. The principle of aircraft detection was widely accepted, but Watson himself was not too happy about it. He considered war a great evil and felt that the production of radar would further encourage it.

It was only in 1935, after realising how urgently Britain needed radars to defend itself, that he finally made the device. In the next few months twenty radar stations were set up. Watson realised that hundreds of operators would be required to work the radar system. He helped in setting up a training school. Furthermore he suggested to a horrified air staff that women should be trained for the job. He felt that women were more conscientious and had a finer sense of touch. Women were trained and they proved their courage and efficiency all through the war. By 1940, fifty radar stations had been set up. It was the aircraft detection system that finally made Britain so powerful. Watson was knighted in 1942. He died in 1973.

Pulse radar is the most widely used type of radar. The diagram
above shows the principal parts of a typical pulse radar set

Transmitting radar waves. The oscillator of a pulse radar set generates a low-power electric signal of a constant frequency. A modulator turns the transmitter on and off, causing the transmitter to produce short bursts of electromagnetic waves. The transmitter produces these high-power waves by amplifying the electric signal generated by the oscillator. A duplexer routes the waves from the transmitter to an aerial. After the waves have been transmitted from the aerial, the duplexer connects the receiver to the aerial, which then collects the waves reflected from an object.

Receiving reflected waves. The switching action of the duplexer enables the receiver to pick up the echoes collected by the aerial. The receiver amplifies the reflected waves and filters out much of the accompanying noise and interference. A signal processor takes the incoming waves from the receiver and combines them, which improves their quality. A display shows the echoes as spots of light or as an image of the object detected. A timer automatically turns the signal processor and the modulator on and off at the right time and so coordinates the operations of the radar set.