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
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.
|(a) The principle of operation
of the RADAR.
However, since the device was operating in a continuous wave
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.
|(b) The display of the transmitted
and reflected signals in the screen of the cathode
Despite of successful pratical demonstrations of the TELEMOBILOSCOPE,
neither government nor private companies were interested in
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
and the PULSE MAGNETRON, gave a great technological advantages
to the Britishes.
|(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.
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.