Page 31 - Radar Technology Encyclopedia

amplifier, summing amplifier, video(-frequency) 21

The weighting factors a are the amplification factors for the Ref.: Skolnik (1990), pp. 4.15–4.19; Andrushko (1980), p. 58; Gilmour
i
individual input signals and are selected in accordance with (1994).
the required rule of summation. Summing amplifiers are usu- tuned amplifier (see resonant amplifier).
ally employed as operational amplifiers. The weighting fac-
A tunnel-diode amplifier is one using a tunnel diode as the
tors are determined by passive elements in the input and
basic component, and frequency-selective circuits or direc-
feedback circuits. IAM
tional filters. Typically, circulators are used at the input of
Ref.: Korn (1952), pp. 11–14, 121–124; Jordan (1985), p. 20.46; Mamonkin
(1977), p. 278. such amplifiers. The operating frequency band is about 0.25
to 110 GHz, gain is 10 to 20 dB, the relative passband is 3.5
A transferred electron effect device (TED) amplifier is one
to 60%, and the typical noise figure is 3 to 7 dB. Along with
based on a TED as the principal amplifying device. The TED
the common structures of amplifiers based on coaxial,
amplifier is a form of single-port amplifier, so it uses circula-
waveguide, and strip lines, the integrated structures based on
tor or hybrid techniques similar to IMPATT circuits. Typical
thin-film technology are also used. The use of these amplifi-
values of bandwidth, gain, and efficiency are 35%, 20 dB, and
ers is expedient in devices where size and weight are the basic
10%, respectively. SAL
constraints, and the requirements to noise levels, dynamic
Ref.: Fink (1982), p. 13.105.
range, temperature range, and input power are not high. In
A transistor amplifier uses transistors as the basic active radars, they are typically used as the amplifiers in phased
elements. The most widely used types in the microwave band arrays modules, and in the second stage of amplification in
are bipolar transistors and field-effect transistors. the receiver after parametric amplifiers. IAM
Transistor amplifiers are used in receiver front ends, Ref.: Rudenko (1971), pp. 14–16, 92–122; Fink (1982), pp. 13.60–13.64.
preamplifiers, and power amplifiers, solid-state transmitter
The twystron amplifier is one based on the twystron tube as
chains, and other radar subsystems and devices. Low-noise
the principal amplifying device. Twystron amplifier band-
amplifiers at a receiver front end are primarily based on
width is from 6 to 15%, peak power is in the megawatt range
Schottky-barrier field-effect transistors and have the follow-
and efficiency is about 30%. Typical twystron amplifier char-
ing characteristics: operating band of 1 to 60 GHz, gain of 15
acteristics are given in Table A6. SAL
to 5 dB/stage, and the noise figure of 0.5 to 8 dB. The pass-
Ref.: Brookner (1977), pp. 314, 315; Skolnik (1990), p. 4.17.
band is from several percent up to a few octaves. Power tran-
sistor amplifiers have the following characteristics per stage: Table A6
Typical Twystron Tube Characteristics
bipolar-transistor-based amplifiers: operating frequency of up
to 7 or 8 GHz, output power is about 5 W, gain is 6-8 dB, and Tube type VA-45 VA-146 VA-915
efficiency at higher frequencies is about 30%; field-effect-
transistor-based amplifiers: operating frequency of up to 80 Frequency band (GHz) 2.7–2.9, 5.4–5.9 3.4–3.6
or 90 GHz, output power of up to 10 W at 10 GHz frequency, 2.9–3.1,
and efficiency of about 20%. IAM 3.0–3.2
Ref.: Gassanov (1988), pp. 168, 196; Fink (1982), pp. 13.106–13.113. Peak power (MW) 3.5 4.0 7.0
A traveling-wave tube (TWT) amplifier is one based on a
Average power (kW) 7.0 10.0 28.0
traveling-wave tube as the basic active component. Depend-
ing on the TWT, linear-beam TWT amplifiers and crossed- Pulse width (ms) 10.0 20.0 40.0
field TWT amplifiers are distinguished (the latter is termed
the magnetron amplifier). Linear-beam TWT amplifiers are Efficiency (%) 35.0 30.0 30.0
classified as low-power amplifiers (up to 1W), power amplifi-
ers (more than 100W), and superpower amplifiers (more than untuned amplifier (see aperiodic amplifier).
100 kW). According to the mode of operation, they are classi-
A vacuum-tube amplifier is one in which a vacuum tube is
fied as continuous-wave and pulsed amplifiers.
the principal amplifying element. The main amplifying tubes
Low-power amplifiers operate in the band of 0.25 to 110
used in modern radar applications are radio-frequency
GHz, amplification band is 30 to 70%, gain is 25 to 35 dB,
devices (see backward-wave tube amplifier; crossed-field
and the noise figure is 6 to 16 dB, for frequencies of 1 to 20
amplifier; klystron amplifier; magnetron amplifier; trav-
GHz and 16 to 20 dB for frequencies of 20 to 100 Ghz. They
eling-wave tube amplifier; twystron amplifier; power
are typically used in the broadband receivers front ends,
amplifier). SAL
where the requirements to noise levels and size are not very
stringent. A video(-frequency) amplifier is one that has an objective to
Power and superpower TWT amplifiers are used in radar amplify the video pulse up to a level sufficient to ensure the
transmitters. Their performance is: efficiency of up to 40%, proper operation of displays. Typically, a video amplifier con-
pulse power of up to 10 MW, gain of 30 to 70 dB, and pass- sists of several stages: video pulses amplifier, video pulse
band of 10 to 15%. These devices require a high-voltage sup- amplitude limiter, and cathode follower for load matching.
ply (up to 100 kW). IAM Logarithmic amplifiers are widely used in such chains to limit