Page 155 - Radar Technology Encyclopedia

display, plan-position indicator (PPI) display, sector 145

bilized PPI (the reference direction remains fixed with respect A P-(scope) display is another name for the plan-position-
to the indicator regardless of the vehicle orientation), delayed indicator type of display commonly known as a PPI display
PPI (the initiation of time base is delayed), off-center PPI (the (Fig. D54).
zero position of the time base is located at a point other than Ref.: IEEE (1993), p. 924.
the center of display, so equivalent of a larger display can be
Range display is a one-dimensional radar display making it
provided for a selected portion of the service area), open-cen-
possible to record and determine the range to a target. It is
ter PPI (the display of the initiation of the time base precedes
usually a CRT (see CRT display) with a static ray deflection
that of the transmitted pulse), and north-stabilized PPI (an
and electronic control unit. Under the effect of the sweep
azimuth-stabilized PPI in which the reference detection is
voltage produced by the control unit and the signals from the
north). This is the type of radar display normally associated
receiver output, an amplitude blip is displayed on the screen
with volume search or surveillance radars that allows a
against the background of a range scale (e.g., a linear scale).
human operator to assess the tactical situation within the
During the return trace of the sweep, the CRT is blanked with
radius of coverage of the radar. The PPI presents a map-like
negative bias to remove blips of noise and false targets.
circular presentation, usually on a CRT (CRT) of azimuth ver-
The range display is characterized by a range scale and
sus range. The display is refreshed at the radar azimuth scan
by the value of the dot of the ray on the screen in kilometers,
rate. Targets and clutter remain visible from scan-to-scan due
representing the resolution of the display.
to the long-persistence properties of the phosphor coating on
The advantage of the range display is the capability to
the CRT’s inside surface. The PPI display may show a full
read signal amplitude. The inability to observe simulta-
360° view, as in Fig. D55, or may be restricted to displaying a
neously on the screen all the targets in the radar coverage
particular sector during each scan or may reflect operation of
zone and to read other coordinates makes it necessary that
the radar in a more limited sector-scan mode.
these displays be employed in combination with other types
of displays in detection and guidance radar. IAM
Ref.: Barton (1964), p. 7; Vasin (1977), p. 182.
A range-height indicator (RHI) is a display on which the
signals are presented in range-height coordinates. (See alti-
tude-range display. SAL
Ref.: IEEE (1996), p. 1,066; Sauvageot (1992), p. 16.
A raw-video display is one that is driven by the analog signal
from the receiver (raw video). This type of display, also
called an analog display, was used in older types of radar and
in modern radar is being replaced by more flexible digital dis-
plays. SAL
Ref.: Skolnik (1980), p. 355.
A rectangular coordinate display has a rectangular screen
that depicts elevation-range, altitude-range, and azimuth-
range in rectangular coordinates. The rectangular coordinate
Figure D55 PPI display for maritime radar, with range rings 5 display provides greater accuracy in the reading of the coordi-
nmi apart (from Skolnik, 1970, p. 31.33, reprinted by permis- nates than the polar coordinate displays using a plan-position
sion of McGraw-Hill). indicator. Examples of this type of display are the B-display,
C-display, and E-display. IAM
The PPI display shown in the figure is typical of older Ref.: Barton (1964), p. 7; Pereverzentsev (1981), p. 364.
displays in which the analog or raw video signal out of the
A remote display is one deployed outside the radar site and
receiver was used to directly drive the display. The arrow
permitting monitoring and display of radar data at a remote
shows the azimuth of a target-borne navigation beacon.
site (e.g., at an air traffic control center). IAM
Though still in use, the analog display is being replaced in
Ref.: Ridenour (1947), Ch. 17; Popov (1980), p. 75.
many modern radars by the digital display, which is driven by
the digital output of the digital signal processor. In digital dis- An R-(scope) display is “an A-display with a segment of the
plays, clutter returns can be suppressed and “true” targets time base expanded near the blip for greater precision in
indicated by synthetically generated symbols. Additional data range measurement and visibility of pulse shape. Usually
relative to each target may also be displayed alongside the tar- regarded as an optional feature of an A-display rather than
get symbol (e.g., digital readouts of target closing speed, being identified by the term R-display.”
engagement priority (for air defense radars), and target alti- Ref.: IEEE (1993), p. 1078.
tude if available). PCH, SAL A sector display produces an enlarged (zoomed) image of an
Ref: IEEE (1993), p. 960; Skolnik (1970), p. 31-33, (1990), p. 1.5. isolated area of space. Two types of sector displays are used: