Radar System Engineering

SEC. 6.51 REPRESENTATION OF THE HORIZONTAL PLANE 167
CRT is used to blank the trace on all but one sweep cycle; a delayed
expanded sweep is thus produced (see Fig. 6.3b).
“Pip-matching” Displuys.-It is frequently useful to compare the
strength of the radar echoes received from a single target by means of
antennas whose patterns differ in direction (see, for example, Sec. 6.13).
For convenience of comparison, the two echoes are usually presented on
the same scope; they can be identified ~~ith the corresponding antenna
by either of two arrangements-the K-scope or the L-scope. The
K-scope (Fig. 6.4a) is so arranged that the range sweeps corresponding
to the two antennas start from different origins, with the result that the
echoes to
@m
be compared are side-by-side. In the L-scope, the signals
from the two antennas produce deflections of opposite sign, the range
(a) Side-by-side presentation (K-scope). (b) Back-to-back presentation (L-scope).
Signalreturr,from the right lobe is the Signal return from the right lobe is the
stronger.
stronger.
FIG. 64,-Pip-matching displays.
origin being common. The signals to be compared thus occur backto-back
(Fig. 6.4 b).
6“5. Representation of the Horizontal Plane .—The large radius of
curvature of the earth and the shallowness of the layer of air above it iu
which conventional aircraft are accustomed to fly make it useful to
project all signals from radar targets in a horizontal plane. Most radar
sets use a sim~le azimuth scan (with a beam that is fanned somewhat
in the vertical direction if aircraft are to be observed), and present their
data on a two-dimensional intensity-modulated display. Even when
target height is important, some’ sort of range-azimuth display is usually
basic to the indication system. The third coordinate usually appears
in a separate presentation on another tube, often as a projection of
all targets on a vertical plane. Intensity-modulated displays of plane
surfaces constitute the most important class of radar indicators.
The Plan-position Indicator.—If the slant range and azimuth coordinates
of the various targets in the field of view are represented, respectively,
by distance from the center of a CRT and by azimuth on the
tube face, the result is a map. Its only defect is the error introduced by
using slant range instead of ground range (that is, slant range times cosine