Page 302 - Radar Technology Encyclopedia

oscillator, backward-wave-tube oscillator, Gunn-diode 292

tial harmonic of the wave (condition of synchronization) and device with a very large memory capacity, which performs
the current is higher than the starting current. This is assured the conversion of w kT into c and s . The latter calculate the
k
k
0
through selection of the slow-wave structure and the electri- readings of c and s using recursive correlations. Recursive
k
k
cal mode. oscillators use special methods of stabilization for prevention
For backward-wave tube oscillators, the dependence of of increasing computation error as k grows. Digital frequency
the frequency of oscillations on the accelerating voltage is synthesizers are used in digital signal processing devices for
characteristic. Backward-wave tube oscillators usually are transfer and inversion of the spectrum. (See also GENERA-
used in continuous mode. The parameters of an oscillator TOR, waveform.) IAM
depend on the type of backward-wave tube. In oscillators of Ref.: Beskin, L. N., Radiotekhnika, no. 4, 1984, pp. 63–65, in Russian.
the backward-wave tube type M, the dependence of the fre-
An extended interaction oscillator is usually a klystron
quency on the voltage is more linear. For electronic frequency
oscillator in which the cavity of the multiresonance klystron
tuning, less of a change in voltage is required in than in type
is replaced by a system of two or several associated cavities.
O backward-wave tube oscillators. Backward-wave tube
A multigap cavity is produced, with whose pole the electron
oscillators of type M have these characteristics: range 1 to 90
flux interactions. Self-excitation arises in the forward spatial
GHz, output power in the CW mode up to several tens of kilo-
harmonic with positive feedback due to reflections from the
watts for decimeter waves, hundreds of kilowatts for centime-
ends of the slowing system. The oscillators have electronic
ter waves, voltage rating of 3 to 4 kV, and efficiency 50 to
and mechanical tuning of the generation frequency, an output
60%. Oscillators of the O type operate in all microwave and
power up to 1 kW at 30 GHz, 20W at 140 GHz in the contin-
millimeter-wave bands with a power from tens of milliwatts
uous mode, and 10 kW at 95 GHz, 10 W at 280 GHz in the
to several watts in the CW mode, voltage rating 2 to 10 kV,
pulse mode. Frequency stability is much greater than in reflex
and efficiency of several percent.
klystrons. They are used in millimeter-band radars. IAM
At present, type M backward-wave tube oscillators are
Ref.: Andrushko (1981), p. 60.
the most powerful oscillators with electronic frequency tun-
ing. IAM A field-effect tetrode oscillator is one that uses a field-effect
transistor with two gates as its active component. In power
Ref.: Andrushko (1981), p. 77; Dubin (1972), p. 71.
generators they are inferior to field-effect transistors, since
A blocking oscillator is a relaxation oscillator of short
they have less power output per unit of gate width. Their
pulses, which constitutes a single-stage amplifier with trans-
basic use is as special circuits for oscillators with higher fre-
former feedback. Owning to the strong inductive feedback,
quency stability, for example for Doppler radars. In master
the blocking generator forms nonsinusoidal, practically rect-
oscillators based on tetrodes, the first half of the instrument is
angular pulses with a duration from units of nanoseconds to
used directly for oscillation, and the second half is a pulse
several tens of microseconds, with a wide range of change of
modulator with a high switching speed. The frequency devia-
their repetition frequency. Blocking oscillators can operate in
tion of such an auto-oscillator at a frequency of 8.6 GHz does
the triggered mode, the auto-oscillation mode, and the syn-
not exceed 300 Hz. Industrial types of microwave tetrodes are
chronization mode. They are used as oscillators for modulat-
used with frequencies up to 12 GHz. The circuit of a com-
ing, synchronizing, blanking and strobing pulses, and
bined oscillator-multiplier, in which the first part of the
sawtooth voltages and currents. IAM
instrument operates as an oscillator, and the second as a mul-
Ref.: Grigor’yants (1981), p. 133.
tiplier, with a frequency of output signal of up to 22 GHz, is
A crystal oscillator can be of the tube or solid-state type and in use. IAM
uses a piezoelectric crystal (usually quartz) as the frequency- Ref.: Joshi, J. S., and Pengelly, R. S., Proc. Int. Microwave Symp., Washing-
determining circuit. The frequency of operation can be from 1 ton, D.C., 1980.
kHz to about 200 MHz when using bulk-wave crystal resona- A grid-controlled (tube) oscillator is an oscillator that uses
tors, and up to 1 GHz for SAW devices. The Q-factor of a typ- oscillator triodes or tetrodes in bands up to 2 GHz. (See tri-
7
6
ical crystal is in the order of 10 to 10 , and stabilities in the ode oscillator.) At present its use is comparatively rare due to
10
order of one part in 10 per day can be obtained. Tempera- restrictions in frequency that lead to a sharp reduction in out-
ture-controlled ovens are commonly used to maintain con- put power with an increase in frequency (inversely propor-
stant frequency within a few parts per million, and control to tional to the square of the frequency).
7
one part on 10 can be obtained by compensation for mea- Typical parameters: peak power 2 MW at a frequency of
sured temperature changes. SAL 425 MHz, high efficiency of 40 to 60%, bandwidth of 1 to 2%
Ref.: Fink (1982), pp. 7.21–7.24. with stage amplification of 10 to 20 dB. IAM
A digital oscillator is a digital device that carries out the Ref.: Perevezentsev (1981), p. 156.
function of an analog oscillator in digital form. A digital A Gunn-diode oscillator is one that uses a Gunn-effect diode
oscillator at frequency w generates, at clock moment kt, a as its active component. Microwave oscillations in the cavity
0
pair of outputs c = cosw kT and s = sinw kT, where T is the of the oscillator arise as a result of formation and movement
k
k
0
0
clock interval. We distinguish between table and recursive of domains that give up their energy in the braking half-peri-
oscillators. The former are realized using a permanent storage ods of the variable field (see GUNN effect). The basic operat-