Radar System Engineering

f+Ec. 62] DEJ’I.VITIOA-S 161
types, without attention to the functional requirement which has called
each into being, and without a description of the technical means of
realizing such indications. The latter subject is undertaken in Chap. 13.
The postponed discussion of radar functions, and of the choice of im~ortant
~adar properties to fit these functions, is found after this cat al ogue
of indicator types.
TYPES OF RADAR INDICATORS
BY L. J. HAWORTH
62. Definitions.-The device that presents radar data in observable
form is called the indicator. It is usually a cathode-ray tube; alternatively
it may be a loudspeaker or telephone headset, a flashing light,
a moving-coil meter, or a pen-and-ink recorder.
The cathode-ray tube (CRT) permits an interpretation of electrical
phenomena in terms of a picture painted on a phosphorescent screen by a
sharply focused beam of electrons controlled in position and intensity by
electrical signals. It is capable of using and displaying many millions
of separate data per second. The geometrical expression which the CRT
gives to electrical phenomena is peculiarly appropriate to radar, because
a geometrical situation involving the various radar targets is precisely
what must usually be represented. Of the other devices mentioned as
possible indicators, only the pen-and-ink recorder is capable of giving
such a geometrical interpretation, and it is slow and cumbersome by
comparison.
Thus, in spite of certain inadequacies, a cathode-ray tube is used
as the radar indicator in all situations that involve any appreciable
target complexity. The picture presented on the tube face is called the
indication, the display, or the presentation. The tube itself is referred
to as the indicator, indicator tube, display tube, CRT, or scope. When a
tube presenting a particular form of display is to be identified, a descriptive
adjective or code designation is prefixed to “scope.” The word
indicator is often extended to include devices and circuits auxiliary to
the cathode-ray tube.
Both magnetic and electrostatic cathode-ray tubes are used (Sec.
13. 1). In their design every effort has been made to achieve the
optimum in resolution, light intensity, deflection sensitivity, and compactness.
The materials (phosphors) used in the screen are of particular
importance. If, as is usually the case, the scanning interrupts the picture
for longer than the retentivity time of the eye, it is necessary to introduce
persistence into the screen. Screens of various rates of decay are available
for this purpose. The detailed characteristics of the tubes, including
the screens, will be discussed in Sees. 13.1 to 133.