Page 216 - Radar Technology Encyclopedia

gate, rectangular generator, sweep 206

width. When an angle gate is used to select and integrate with an electron beam. The produced resonance structure is
input pulses for tracking in a sector-scanning radar, its opti- capable of holding only the operating oscillation and maxi-
mum shape is that of the received pulse envelope (the two- mally suppressing (to a level of -100 to -120 dB) the second-
way beam shape), but the loss from use of a rectangular gate ary types. IAM
may not be large enough to warrant the more complicated Ref.: Nefedov (1986), p. 157.
matched gate shape. DKB
A mark generator is a device for generating and shaping
A sampling gate is a time gate use to select a given group of scale marks on radar displays. The generator is started at the
pulses or signals for subsequent processing. It may be imple- moment of radiation of the transmitted pulse. The mark
mented in range-delay time, scan-cycle time, or any other pulses exist only during the direct track of the beam of the
domain in which signals are available for sampling. cathode ray tube. The range-mark generator consists usually
of a shock-excited oscillator and a diode limiter, which con-
A split gate is a tracking gate designed to sense the departure
verts the sinusoidal signals into pulses, a differentiating stage
of the centroid of a signal pulse from the center of the gate.
that synchronizes the blocking oscillators generating the
The two halves of the gate are generated with opposite polar-
marks of the different scales (for example 5 km and 10 km
ity and followed by an integrating circuit (narrowband or
range marks), and a mark mixer.
low-pass filter). The portion of the input pulse received dur-
The generation of azimuth marks of a radar with rotating
ing the leading half (early gate) is passed with a positive
antenna is controlled by a photoelectric modulator located in
,
polarity (or 0 phase) and that received during the lagging half
the pedestal of the antenna system. Such a generator consti-
(late gate) is passed with negative polarity (or 180° phase).
tutes a circuit for processing the pulses of the photomodulator
The integrating circuit, at the end of the split-gate, then has a
(change of leading edge, reduction of duration for their con-
residual voltage proportional to the position of the signal cen-
version into marks of the required parameters). IAM
troid relative to the center of the gate. This voltage is used as
Ref.: Penrose (1959), p. 225; Perevezentsev (1981), pp. 357, 359.
the input to a tracking loop, which holds the gate centered on
the target. (See DISCRIMINATOR, time). A pulse generator is an electronic circuit creating video
A split angle gate is used in locating the centroid of the pulses of various amplitude, length, and relative pulse dura-
envelope of echo pulses received in a sector-scanning radar, tion. In terms of operating principle they are divided basically
which represents the time at which the beam is pointing at the into blocking oscillators (single-stage oscillators with trans-
target. The circuit operates in the same way as the split gate former feedback), multivibrators, and flip-flops (two-stage
for ranging, except that its input is the envelope of pulses oscillators with capacitive and potentiometric connections
received during the scan, and the duration of the gate is respectively between stages).
matched to the time required to scan through one beamwidth. It may also be an instrument belonging to a group of
Ideally, to minimize effects of thermal noise, the shape of the pulse test oscillators. It is widely used in tuning and testing of
gate will be matched to the derivative of the two-way beam radar equipment, for time measurement, for modeling of peri-
pattern. To minimize the errors caused by target fluctuation, odic processes, and so forth. IAM
the gate may be extended toward the skirts of the beam Ref.: Popov (1980), p. 82.
pattern. DKB
A signal generator is a radio-frequency generator in which
Barton (1988), pp. 390–397, (1988), pp. 435–437; Skolnik (1990), pp.
the frequency, amplitude, and depth of modulation can be
18.27–18.30.
changed over broad limits. Signal generators include sweep
A tracking gate is a range, angle, or velocity gate used in generators, test generators of pulses of various shapes, ran-
tracking a particular target, either in a radar dedicated to that dom-signal generators, and so forth. Signal generators are
target or in a track-while-scan radar. often used as simulators of radar signals and for testing and
A velocity gate is actually a filter used to track targets in the tuning of radar circuits. IAM
doppler frequency domain. This filter may be a bandpass fil- Ref.: Van Voorhis (1948), p. 278; Gold (1969, 1973), p. 169, in Russian.
ter to select target as inputs to angle tracking or AGC circuits, A sweep generator is a voltage or current generator of a spe-
or a discriminator (analogous to the split gate in range track- cial form intended to produce a time sweep in radar displays.
ing) to develop a doppler loop error signal. The voltage generators are used in cathode-ray tubes with
electrostatic control, and current generators with electromag-
velocity gate pull-off (see ECM, velocity measurement).
netic control. Depending on the type of sweep, sawtooth volt-
GENERATOR age (current) generators are used to form linear coordinate
sweeps, and generators of signals proportional to the sine and
boxcar generator (see CIRCUIT, sample-and-hold).
cosine of the turning angle are used for a circular sweep
A diffraction radiation generator is a device producing (sweep in polar coordinates).
radiation in the millimeter or submillimeter bands with very Digital generators are used along with analog sweep gen-
low levels of secondary oscillations. The generator contains a erators (see pulse generator). The digital circular sweep gen-
diffraction grid over which the electron flux is distributed, erator contains a generator of pulses of frequency f, which is
and an open cavity. The first spatial harmonic is synchronized