Page 278 - Radar Technology Encyclopedia

mixer, Josephson-effect mixer, transistor 268

evaporation technology. The separate component or the grid A Schottky-barrier-diode mixer is one using a Schottky-
of the components is typically mounted in a waveguide mix- barrier diode as an active component. Typically, these mixers
ing structure analogous to those of Schottky diodes. Because are used in a millimeter wave and a submillimeter wave band.
of the extremely sharp volt-ampere characteristic, the power The best noise performance is achieved for the sharp volt-
of the local oscillator can be less than 1 mW. This type of ampere curve. In a 3-mm band under ambient temperature,
mixer is especially efficient at very high frequencies (e.g., at the noise temperature is about 400 to 700K, and losses of 4.5
452 GHz), and has a noise temperature of 350K and a 5-dB to 7 dB. For cooling down to 20K, these parameters are 70 to
conversion loss. 200K and 5 to 7 dB respectively. Cooled mixers require the
IAM power of the LO to be about 50 to 500 mW. A typical milli-
Ref.: Reysanen, A., Zarubezhnaya Radioelektronika, no. 11, p. 67. meter-wave mixer is a semiconductor IC, with more than 100
Schottky contacts which are inserted in the waveguide. (See
A low-noise mixer is one providing relatively low noise level
multidiode mixer.) IAM
at the frequency converter output. The main types of such
mixers are transistor mixer, Schottky-barrier diode mixer, and Ref.: Fink (1982), p. 14.61; Reysanen, A., Zarubezhnaya Radioelektronika,
no. 19, 1984 (in Russian).
Josephson effect mixer (Table M3). Tunnel diode and inverse
diode mixers are also used as low-noise mixers. Typically, A mixer spurious-effect chart is a chart depicting the spuri-
low-noise mixers employ balanced circuits (see balanced ous components arising from the nonlinear nature of mixer
mixer).IAM operation. There are several forms of such data representa-
Ref.: Gassanov (1988), p. 134. tion, one of them is shown in Fig. M11. Here the higher input
frequency is designated by H and the lower one by L. The
Table M3 response caused by the first-order mixer product (H-L) origi-
Main Types of Low-Noise Mixers nates mainly from the square-law term in the series describ-
ing the dependence of the current flowing in nonlinear
Operating resistance from the voltage across the resistor terminals (see
Mixer frequency, Noise factor, dB MIXER), and the variation of normalized output frequency
GHz (H-L)/H with normalized input frequency L/H are shown
with heavy lines. All other lines in the chart depict spurious
Transistor mixer 5 to 30 5 to 16
effects originating from high-order terms in the series. This
Schottky-barrier diode 50 to 600 5 to 7 (100 GHz) chart is convenient when one wants to see at a glance which
mixer combination of input frequencies and bandwidths are free of
strong low-order spurious components. SAL
Josephson effect 300 to 600 5 to 8
Ref.: Skolnik (1990), pp. 3.8–3.10.
mixer
A multidiode mixer is an integrated-circuit-technology-
based mixer employing double-diode balanced mixers and
their combinations. The main advantage is that this mixer is
based on the up-to-date integrated circuit technology. The
high quality and identity of IC mixing diodes makes it possi-
ble to ensure decoupling of LO and signal sources without
using bulky frequency-selective circuits, to suppress LO
noise and sidebands, to reduce the conversion losses by
returning to IF the power of the signal converted at one of the
sidebands, and to ensure phase decoupling of both channels.
Typically, multidiode mixers are based on monolithic ICs and
are used in receiver frequency converters and active phased
array transceivers in millimeter waveband. IAM
Ref.: Rozanov (1989), p. 74.
A point-contact diode mixer is one using the conventional Figure M11 Downconverter spurious-effects chart. H = high
point-contact diode as the nonlinear device providing fre- input frequency, L = low input frequency (from Skolnik, 1990,
quency conversion. In comparison, the Schottky-barrier diode Fig 3.2, p. 3.9, reprinted by permission of McGraw-Hill).
mixer it has better burnout properties, but higher noise figure
The transistor mixer uses as an active element a transistor,
than the point-contact mixer. SAL
typically a bipolar transistor or a field-effect transistor. In a
Ref.: Skolnik (1980), p. 347.
microwave band, Schottky-barrier field-effect transistors are
quasioptical mixer (see Josephson-effect mixer). typically used because they have a lower noise level and can
operate more efficiently at frequencies higher than 10 GHz.
Transistor balanced mixers and broadband mixers based on