Chapter One
Early Days - the concept of Radar
RADAR - RAdio Detection And Ranging, following half a century of radio development successful radar systems were developed quite independ-ently in England, America, France and Germany during the latter part of the 19 301 s. Hertz first showed that radio waves were reflected from solid objects. Hulsemeger, a German engineer, was granted a patent, in several countries, as long ago as 1904 on a proposed method of using this property as an obstacle detector and navigational aid for ships.
British Radar, fortunately, was the quickest to be developed, almost certainly due to the immediate threat of the War. During the winter of 1934- 1935 the Air Ministry set up a Committee for the Scientific Survey of Air Defence. At the time a young Scottish physicist was head of the radio department of the National Physical Laboratory. His name was to become known world-wide in connection with the development of RADAR. He submitted a plan for the detection of aircraft by a pulse method to the newly formed committee. It was accepted and this first experimental radar system by Robert Watson- Watt (later knighted) was set up in the spring of 1935.
Summer development led to the detail of the Chain Home (CH) stations by winter 1935, erection of the stations beginning in 1936.
Early research was carried out at Slough under the direction of Watson-Watt, men of the calibre of Bainbridge-Bell were in the team. The whole development throughout was kept very quiet, security was exceptionally tight. When the Government became interested - the Ministry of Defence realised the potential of Radar as a weapon - they set up their Research Establishment at Bawdsey Manor, on the bank of the River Deban opposite to Felixstowe Ferry, Suffolk. Here again the tightest possible security prevailed, indeed the only transport between the establishment and the mainland was a small rowing boat I The year was 1937 and it was here that the early radar research and development took shape. The sole contractor at the time was A.C. Cossor, and systems were developed at the Cossor establishments at Highbury and Hackney in London. The test sites were very small - at Hackney the small laboratories were under the railway lines while at Highbury the roof was employed as the radar testing site - the BBC unknowingly provided an excellent testing target in Alexandra Palace, which was clearly visible from the rooftop.
The Chain Home stations erected in 1936 were early aircraft-warning radar - the first ever radar to have actual combat use. Initially there were five stations separated by some twenty-five miles and set up to protect London. When war broke out in 19 39 the chain' had been extended to, beitween sixty arid seventy stations, with improved equipment, all along the coast and forming the basis of the British reporting system for the greater part of the War. Undoubtedly the system saved the country from defeat in the Battle of Britain and towards the end of the war was invaluable in the detection and tracking of the V- 2 rockets. There were faults in the system - it was discovered later than by flying low enough, aircraft could creep in under the radar cover - but its very existence when the war broke out brought tremendous strength to our defence system.
In 1939 a British radar engineer produced an invention which was to revolutionise the radar industry of the future. Unfortunately, as with many new developments, the Government was slow to realise its potential. The invention concerned a new type of display, the only one available at the time was the 'A' trace (Fig. 1). Now this system provides range information relating to targets only in the direction in which the aerial is pointing and obviously obtaining a complete picture of the surrounding area by this method is extremely tedious.
In 1939 John Godeck (of Advanced Systems Group, Cowes), then with the radar group at Cossor, invented the Plan Position Indicator (P.P.I.). He developed a method by which the time base was rotated in conjunction with the aerial and in this way produced a 'plan' of the surrounding area, the rotating time base was produced electrically.
By varying the instantanious amplitude of the oscillator causing the electron beam rotation, the diameter of the circle is changed in sawtooth form to scan in azimuth and range, the video signal being used to vary the beam intensity. (Fig. 3).
Unfortunately, as stated, the Government was slow to react. The Air Ministry turned down P. P. I. A Patent was taken out in Cossor' s (and Godeck' s) name and after about eighteen months the Air Ministry finally realised the usefulness of the P.P.I. and it started to become the standard radar display. Later, after design work on guided weapons, satellites etc., John Godeck, whose original invention this was, joined Plessey Radar at Cowes. His distinguished career in radar has continued and he is still at Cowes today.
At first, then, all radar development in this country took place under Cossor, here, too, the first airborne radar was developed. There were two types : ASV (air to surface vessel) and AI (air interception). The ASV type equipment was successfully demonstrated in 1938, the AI by June 1939, it is incredible to note that by the time war broke out in September 1939 the latter system had already been installed in four aircraft and by the end of September, thirty aircraft carried it.
With the development of airborne radar it soon became obvious that if sharp radar beams were to be produced by antennae small enough to be carried in an aeroplane, wavelengths far shorter than the 1½m in use in early equipment would have to be employed. The result was the tremendous effort that went into producing the MAGNETRON TRANSMITTER - a microwave oscillator that was capable of giving out pulse power adequate for radar use. This remarkable develpment by 1940 heralded the beginnings of modern radar history. It was essential that a new type of transmitter should be developed -the conventional types posed insoluble problems in modification.
As a source of high-power microwaves the magnetron oscillator was spectacular. To compare : at 3000MHz average magnetron power output is several hundred watts, triode output would be but a few watts.
Naturally all the early work was with thermionic valves, and frequencies attainable were limited to 200 MHz, above this the gain fell off considerably. The only valves capable of handling this were the 'acorn' triodes and pentodes (so called because of their resemblence to an acorn). There were no signal generators around at the time, to determine the performance of a receiver a reflection was obtained from a known target . The technique used was to see if the receiver was more efficient than the last one you produced It was not until 1941 that Marconi produced the first signal generator.
The Cossor domination ended with the entry of Metropolitan Vickers onto the radar scene, they took over the transmitter/receiver aspect. Others came in gradually - much later on - Marconi, E. M.I. (then HMV) and gradually the industry began to develop. Early developments included : SLC (Search Light Command) - radar coupled to searchlights to enable them to be directed at an aircraft ; G. L. (Gun Laying) Equipment (Messrs. L.H. Bedford and O. S. Puckle) - for ranging ship guns, installed initially on cruisers - the Gun Laying Officers used optical methods for range finding and when radar methods first came in they were reluctant to use the new technique : if the radar reading did not agree with the optical reading they took the latter ! However, with greater experience they soon realised the benefits of radar.
These then were the early days of what was to become a rapidly expanding industry. The technical achievement represented by wartime development of radar seems very nearly unparalleled. In the time between 1934 and 1940 radar development had turned the aeroplane into a sophisitcated and powerful weapon. In the next chapter we will look at the Decca Company and how their interest in radar developed.