Page 149 - Radar Technology Encyclopedia

discriminator, time-frequency display, alphanumeric (data) 139

Ref.: IEEE (1993), p. 369; Poole (1966); Skolnik (1970), Ch. 6, (1980),
t D
Time Ch. 9; Bystrov (1985).
discriminator
An active display is based on conversion of electrical energy
y(t)
into luminous energy through various physical effects
(Table D8).
f D One of the basic parameters of active displays is the light
Frequency
discriminator output of the device, which defines the power consumed by
2
the display at a normal level of brightness of 350 cd/m .
In contrast to passive displays, active displays have
greater brightness, good multiplexing capabilities, and better
Reference
voltage quality of reproduction of color images. The CRT display is a
generator common example of an active display.
t f
e e Table D8
Figure D46 Time-frequency discriminator (after Shirman, Types of Active Displays
1981, Fig. 14.12, p. 214).
Max.
the time and frequency discriminators. Time-delay error is Type of display Physical effect light
generated in the time discriminator, while frequency error is output
lm/W
generated in the frequency discriminator. AIL
Electron beam High voltage cathode luminescence 100
Ref.: Shirman (1981), p. 214.
Vacuum luminescent Low voltage cathode luminescence 5
Video discrimination is the process used to reduce the fre-
Gas discharge Radiation of gas discharge 5
quency band of the video amplifier stage in which it is used.
Electro-luminescent Pre-breakdown electrolumines- 20
SAL
cence
Ref.: Johnston (1979), p. 68.
Semiconductor Injection electroluminescence 30
DISH (see ANTENNA, reflector).
Semiconductor displays are active displays based on the
DISPLAY, radar. A radar display is an electronic instrument
effect of an injection luminescence that takes place when the
for visual representation of radar data. Radar displays can be
carriers are recombined on a junction of the semiconductor
classified from the standpoint of their functions, the physical
crystal switched in the forward direction.
principles of their implementation, type of information dis-
Semiconductor displays are also known as light-emitting
played, and so forth. From the viewpoint of function, they can
diode displays. They are characterized by a low operating
be detection displays, measurement displays, or special dis-
voltage, the ability to overlap with semiconductor logic cir-
plays. From the viewpoint of number of displayed coordi-
cuits, small dimensions, a long service life, a high degree of
nates, they can be one-dimensional (1D), two-dimensional
pixel brightness, and a capability for multiplex addressing.
(2D), or three-dimensional (3D). An example of a 1D display
Matrix displays with 6,000 to 40,000 elements have an 0.8-
is the range display (A-scope). Most widely used are 2D dis-
mm space between the elements, a brightness of 140 to 240
plays, represented by the altitude-range display (range-height 2
candles/m , a power consumption of 2 to 112W. IAM
indicator, or RHI), azimuth-elevation display (C-scope), azi-
Ref.: Bystrov (1985), p. 98; Fink (1982), pp. 11.55, 23.75.
muth-range display (B-scope), elevation-range display
An alphanumeric (data) display provides numerical and
(E-scope), and plan-position indicator (PPI). These letter
alphabetical information. Typically, character-modulating and
descriptions date back to World War II, and many of them are
character-synthesizing alphanumeric displays are distin-
obsolete. From the viewpoint of physical implementation,
guished. In the former case, a light or electronic beam is
active and passive displays are distinguished. The former are
shaped into the form of a character (e.g., CRT displays with
represented mainly by cathode-ray-tube (CRT) displays and
character-shaping matrices). An electronic beam passing
semiconductor displays. Passive displays can be of liquid-
through the lower part of the matrix “prints” the character on
crystal or ferroelectric types. In most radar applications CRT
the screen. In character-synthesis displays the characters are
displays remain the best choice because of their good perfor-
formed based on the mosaic principle. In this case shaping
mance and low cost.
takes place by means of an image mosaic independent of the
From the viewpoint of displayed information, displays
controlled elements, each being a light-signal converter. The
can be classified as presenting radar signal data, alphanumer-
following displays are based on the principle of image shap-
ics, or combined displays. These can be driven by analog data
ing: segment character synthesizing displays, the elements of
(analog or raw-video displays) or digital data (digital or syn-
which are segments and grouped in one or several character
thetic-video displays). Displays in modern radar are typically
locations; matrix character synthesizing displays, the image
synthetic-video combined displays, often using the monitors
elements of which form an orthogonal matrix; and mnemonic
of computer-based work stations. SAL