8.2.2 - THE RADAR

RADAR is an acronym for: RADIO DETECTING AND RANGING, term adopted for the first time in 1941, by the American navy. In the reality, it is a radio technique that uses the emission of signals modulated in microwaves, whose analysis of the reflected pulses allows the localization of an
(a) The principle of operation of the RADAR.
object or even its speed. (a) It was originally devised as an early warning process to detect the approaching of hostiles aircraft to enable defences in order to counter react in sufficient time. However, considering its ability to measure the range and target direction were additional advantages allowing improved defensive deployment. (b) The actual concept of reflection off a body and hence of detection was first proposed by Tesla in 1900. Christian Hulsmeyer invented and patented the first practical radar in 1904. His apparatus called "TELEMOBILOSCOPE", consisted of a spark gap transmitter operating in the frequency range of 650 MHz, whose emissions were focused by a parabollic antenna located on the mast of the ship. The receiving antenna picked up the reflected signals and in this way, when a ship came within a certain distance a bell was automaticallly rung.
However, since the device was operating in a continuous wave not in
(b) The display of the transmitted and reflected signals in the screen of the cathode ray tube
pulses it could not make measurement of distances of the object. To skirt this difficulty, the antenna was pointed directly down toward the water. Thus, the waves reflected off the surface and hit the target. Now, the range could be calculated from the antenna angle and knowledge of its height above the water.
Despite of successful pratical demonstrations of the TELEMOBILOSCOPE, neither government nor private companies were interested in the same.
However, it was only during the WWI that the military need for some form of target detection to improve on the performance of the human eye that the researches were started for attainment of an operational device for object detection at long distances. They were made simultaneously in several countries under several denominations as, for example, FUMG, Funkmess Gerät, in Germany, DEM or Detection Eletromagnetique in France and, in England, RDF, or Radio Direction Finding. In 1935, R. A. Watson-Watt and A. F. Wilkins performed the practical demonstration of radar that led to the rapide development of such long-range detection technique in England.
Due to the proximity, the war around 1938 the pace of radar development then quickened in Germany, England and in Japan. In Germany the studies about the RADAR started in 1933, under the supervision o dr. Rudolph Kuhnold. The German Armed Forces employed several types of Radar such as: FREYA, SEETAK, LICHTENSTEIN and WURZBURG. This last one was the base for the development of the Japanese RADARS type TAKI-6 and TAKI-1.
On the other hand, England, through the studies of Watson-Watt, it was far ahead on the RADAR development that in parallel with the breakthrough in component researches as the new valves for high fequency applications as the KLYSTRON
(a) The ASV Radar comprises a transmitter and receiver provided with two antennas type YAGI. Such kind of antennas was developed in 1921, by the Japanese researchers H. Yagi and S. Uda of the University of Tohuku.
and the PULSE MAGNETRON, gave a great technological advantages to the Britishes.
Thus, in 1937, the Ministry of Desfense started to build the BRISTISH HOME CHAIN that was installed along the east and south coast of England to give early warning approaching of aircraft.
This remarkable radar system played its decise role in the war, during the battle of England, when such line of electronic defense could quickly detect the German aircrafts flying over 3000 m, in distances of 180 km, thus allowing, improved defensive deployment.
During the conflict, the Bristish had still developed others types of RADARS, for tatictal and strategic applications. Amongst them are: the type "Gun Laying"; the "Chain Home Low Flying", to detect aircrafts flying in low altitude; the FFI system an acronym for "indentification friend or foe" used to differentiate between a friendly and an enemy target, the famous RADAR ASV," Airborne Detection of Surface Vessels" as aforementioned responsable for the destruction of the German submarine fleet. Finally, the RADAR plan position indicator, which in the reality was an innovation of RADAR CHL.
As one could see, pressed by the war that threatened his territory, the Bristih in a short period of time - 1936-1940, developed almost alone all the RADAR technology, whose influences are still felt currently. (b)

(b) The principle of operation of the RADAR plan position indicator.
(a) The RADAR PPI in operation.
(f) A modern RADAR PPI.