Page 303 - Radar Technology Encyclopedia

293 oscillator, Gunn-diode oscillator, resonant

ing mode of the diode in the oscillators is the mode of limited They are used in low-power transmitters of radar naviga-
accumulation of volume charge (LAVC). To produce this tion apparatus and as microwave local oscillators. IAM
mode, a constant voltage greater than critical is applied to the Ref.: Andrushko (1981), pp. 30, 43; Perevezentsev (1981), p. 158.
diode, which is contained in a high-quality cavity, and the
local oscillator (see LOCAL OSCILLATOR).
oscillating system is tuned to a frequency is many times
greater than the transit frequency (up to several gigahertz). magnetron oscillator (see MAGNETRON).
Frequency retuning is possible in a band higher than an
A master oscillator is a source of microwave (RF) oscilla-
octave. The power of the oscillators amounts to units of Watts
tions, operating in a given frequency range with the necessary
in continuous mode, with an efficiency up to 15 to 20%, and
frequency stability. A master oscillator is usually a low-
units of kilowatts in pulse mode. In practice, hybrid modes
power, high-stable (transistor, tube, etc.) auto-oscillator and is
combining the LAVC mode with other domain modes, and
used for excitation of oscillations, which are then amplified in
possessing less sensitivity to changes in parameters and loads
subsequent stages.
are widely used. Stabilization of the supply voltage is
One distinguishes between single-circuit auto-oscillators,
required for stabilization of the operating mode.
which are composed in an inductive or capacitive circuit;
Compared with the avalanche transit-time diode, Gunn-
double-circuit, which are implemented with series connection
effect diode oscillators have less power, less noise level, and
of an additional circuit to an anode circuit of any single-cir-
lower supply voltage (up to 10V). In the decimeter, centime-
cuit oscillator; and auto-oscillators with transformer feed-
ter, and millimeter bands, Gunn diodes put out hundreds, tens,
back. (See blocking oscillator.) The frequency of the
and units of milliwatts, respectively.
generated oscillations in master oscillators is usually close to
The fields of application are roughly the same as in ava-
the natural frequency of the circuit and may be changed over
lanche transit-time diodes. Gunn-diode oscillators are used as
wide limits by the tuning elements. IAM
local oscillators in the millimeter band, and harmonic oscilla-
tion modes are used in frequencies above 100 GHz. IAM Ref.: Popov (1980), p. 128.
Ref.: Gassanov (1988), p. 186. A monotron oscillator is one in which the continuous elec-
tron beam transfers energy to the electromagnetic field in the
A gyrotron oscillator is one based on a gyrotron. It is the
individual resonant cavity. The use of high-quality supercon-
most powerful and efficient source of power in the millime-
ducting cavities makes it possible to design powerful
ter-wave band, capable of operating in long-pulse modes (up
monotron microwave oscillators whose frequency stability is
to 75 ms) or the CW mode. The efficiency of gyrotron oscilla-
as high as that of crystal oscillators. IAM
tors in the short-pulse mode reaches 65%, and the output
power in the CW mode is more than 200 kW at a frequency Ref.: Popov (1980), p. 238.
up to 70 GHz. Powerful oscillators (up to 1 MW) are made in A nonresonant oscillator is an electronic device with one or
the higher frequency range of 100 to 200 GHz. multiple interactions in which the oscillating system in the
Gyrotron oscillators are used in developmental radars operating frequency band does not have resonant properties
and communications systems in the millimeter-wave band and is excited in the traveling electromagnetic wave mode.
and also for heating plasma in large-scale tokamacs. IAM Examples of such devices include the traveling-wave tube,
Ref.: Temkin, R. J. et al., Int. J. Infrared and Millimeter Waves, 1982, vol. 3, the backward-wave tube, and the stabilitron. (See also travel-
no. 4; Carmel, Y. et al., Phys. Rev. Let.t 50, 1983, no. 2. ing wave tube oscillator and backward-wave tube oscilla-
A klystron oscillator uses a klystron as its active component. tor.) IAM
They may be based either on a reflex \klystron or on a transit Ref.: Popov (1980), p. 382.
klystron. In the transit klystron, self-excitation is provided by A radio-frequency (RF) oscillator is a generator of electro-
feedback between the output and input cavities, connecting magnetic oscillations in the bands 100 kHz to 100 MHz. The
them by a coaxial transmission line. The length of the line RF oscillator is used as the basic element of radio transmitters
provides the necessary phase of the oscillations applied to the in this range, and low-power RF oscillators as local oscilla-
input. Excitation occurs when the current is above a certain tors of superheterodyne receivers. IAM
threshold (starting current). Ref.: Popov (1980), p. 81.
The maximal output power and the efficiency of klystron
A resonant oscillator is an electronic device that creates dis-
oscillators are the same as for transit klystron amplifiers.
crete types of oscillations. Such oscillators are based on the
Transit-klystron oscillators have comparatively limited uses,
short-term interaction of electrons with the electronic field in
basically in the range of 5.5 to 44 GHz as highly stable
the gap of a hollow cavity. These include devices with long
medium-power oscillators (0.2 to 200W) of doppler radars,
and multiple interactions, whose slow-wave system operates
radio beacons, and also for pumping of parametric amplifiers.
in the standing-wave mode and forms an oscillating system
Reflex klystrons are widely used as low-power (0.1 to
with discrete types of oscillations. Examples of such oscilla-
1W oscillators, thanks to their design simplicity, and the
tors include microwave triode and tetrode oscillators (see
capacity for electronic frequency tuning (usually amounting
to ±10 to 15%).