Radar System Engineering

194 THE GATHERING AND PRESENTA TIQN OF RADAR DATA [SEC. 6.12
h = D sin A+. But D’ = R’ – h’, so that
h = (1 ?
Tn2A;4)%”
This simple relation permits height to be found if the target range
and the difference angle can be determined. There is a danger that at
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Radar
AD
FIG.6.26.—Schematicview of V-beam principle. For clarity, vertical and slantbeamsare
shown without the 10°separationin azimuth whichis usedin practice.
low elevations the two signals from the vertical and slant beams might
be displayed so close together that no height can be found. Thk problem
is eliminated by introducing a fixed separation of 10° between the beams,
so that there is a 10° separation between the signals even from a target
at zero altitude. The indicator is designed around the general principle
of a B-scope in that range is presented against angle. The simplest form
of indicator has range along the horizontal axis and Ad on the vertical
axis (Fig. 6.27). Suppose a target
appears at A on the vertical beam
at an azimuth selected by the
operator. Video output from the
Slantbzam
videosignals vertical beam appears on the scope
for 10° of azimuth rotation centered
on the selected azimuth. It
is then blanked out and slant video
substituted. If the target is at
Vytical.beam zero elevation, the slant beam will
wdeosignals
illuminate it 10° later, at A‘. If
the target has a definite height,
10 20 30 40 50 60
Rangem miles --
the slant beam will rotate further
FIG. 627.-Simple V-beam indicator. Lines before illuminating it and the
of constant height are shown,
signal will actually appear at B, as
shown. A movable overlay superimposed on the scope face is set so that
its baseline bisects the first signal at A The 10° delay position is marked
by a second line, which serves as the zero-height line for a succession of
constant-height lines which appear as drawn. Height is estimated
directly from the face of the scope. The two signals from a single target
(e.g., A and B) always appear at the same range.