Radar System Engineering

440 THE RECEIVING SYSTEM—RADAR RECEIVERS [SEC.122
tion system, the display circuits can be identical with those of the B-scope
of Fig. 12.1.
Figure 12”3 shows the parts necessary to convert Fig. 12.1 to an
“electronic” PPI without moving parts, or by a slight variation into an
RHI. The range sweep of a PPI can be considered as made up of two
orthogonal sweeps with speeds proportional to sin 0 and cos o (see sketch
4Antenna
e
I
transmitter
c1Data
Fm. 12.2.—Rotating-coilPPI.
]#21RM=,—w
o ~.
I
r?-t-—L~
rrewver
‘- ~ “ Amplifier
%1 I
Rcmoe
‘LJ
=
ClactronicPPI
Waveforms
(a) Trigger
Jllllll
(b)fime~se (~)w-----––---u
(c)Rein e
(~ RC099
——— ——— —.— +1111111
.
+ ‘z
~@
K,Rwac
~ ma
FIG. 12.3.—Electronic PPI and RHI.
in Fig. 12.3). In this particular form of PPI, these sweep “components”
are formed by passing a sawtooth waveform through a sine-cosine
“resolver” on the scanner. The resolver is a variocoupler or a sinecosine
potentiometer which, when excited by a given waveform, produces
two “components” of the same waveform whose amplitudes are proportional
respectively to the sine and the cosine of the orientation angle of
the resolver. Proper amplifiers are provided for driving a pair of orthogonal
coils (as indicated in Fig. 12.3) or, alternatively, the deflecting
plates of an electrostatic tube.
‘3