Page 276 - Radar Technology Encyclopedia

MICROPHONE [MICROPHONIC] EFFECT mixer, crystal 266

MICROPHONE [MICROPHONIC] EFFECT. The micro- control system. The antenna system as a rule contains one or
phone effect is the changing of the electrical parameters of the several parabolic reflectors with horn elements, and also
components and circuits under the effect of mechanical jolts devices that scan the beams. Receivers in antiradiation mis-
and oscillations. The microphone effect can create parasitic siles used against radars operating at constant carrier frequen-
noise components, and sometimes also passive interference. cies are narrowband. Antiradar missiles with wideband
The effect is reduced by increasing the strength and rigidity of receivers are used against radars whose frequency is
microwave and other elements subjected to vibrations, as well unknown or known only approximately. Such receivers have
as by employing compensation using a servo system in the lower sensitivity and selectivity. The warhead is detonated by
event that the effect occurs at low frequencies. IAM a proximity fuse at the moment that missile closes with the
Ref.: Skolnik (1970), p. 16-6. target, at a signal from the control system, or in case the radar
goes silent by a contact fuse upon impact. IAM
MICROWAVE ADAPTER (see ADAPTER, microwave).
Ref.: Popov (1980), p. 326; Skolnik (1990), p. 19.18.
MICROWAVE AMPLIFIER (see AMPLIFIER).
MIXER. The mixer is “the stage in a heterodyne receiver in
MICROWAVE ANTENNA (see ANTENNA). which the incoming signal is modulated with the signal from
the local oscillator to produce the intermediate frequency sig-
MICROWAVE BRIDGE (see BRIDGE, microwave). nal.” In some radars there may be two or three successive
conversions, with mixers operating first at the RF and then at
MICROWAVE CHOKE (see CHOKE, microwave).
the first (and second) IFs. The main types of mixers are
MICROWAVE CIRCUIT (see CIRCUIT). described below. SAL
Ref.: IEEE (1993), p. 812.
MICROWAVE CONNECTOR (see CONNECTOR,
microwave). A balanced mixer is one providing local oscillator (LO)
noise level reduction by means of phase balance at parallel
MICROWAVE DEVICE (see DEVICE, microwave).
switched diodes. The main structures of balanced mixers are
MICROWAVE DIODE (see DIODE, microwave). double-diode mixers, double-balanced mixers, and circular
and double-circular mixers. The main advantage of a bal-
MICROWAVE HYBRID (see HYBRID, microwave).
anced mixer in comparison with a conventional one is the
MICROWAVE INTEGRATED CIRCUIT (see INTE- reduction in the noise factor by 2 to 10 dB because of phase
GRATED CIRCUIT). suppression of LO noise, improved decoupling of the signal
and local oscillator circuits, permitting use of LOs with lower
MICROWAVE JOINT (see JOINT, microwave). power, higher input power handling capability, and the sup-
pression of the even IF harmonics. In modern receivers, bal-
MICROWAVE MULTIPORT (see MULTIPORT).
anced mixers are typically implemented with IC technology
MICROWAVE OSCILLATOR (see OSCILLATOR). based on Schottky-barrier diodes. The noise factor in a 5- to
10-GHz band is about 7 to 10 dB, and conversion losses are
MICROWAVE RADIOMETER (see RADIOMETER).
about 5 to 8 dB. IAM
MICROWAVE RESONATOR (see RESONATOR). Ref.: Gassanov (1988), pp. 116, 118; Skolnik (1990), pp. 3.7–3.17.
A circular mixer is one using a balanced diode bridge. The
MICROWAVE SWITCH (see SWITCH).
signal and local oscillator (LO) voltages are applied to the
MICROWAVE TETRODE (see TETRODE). orthogonal diagonals of this bridge by two matching trans-
formers. The IF signal is filtered by means of microwave
MICROWAVE TOMOGRAPHY (see TOMOGRAPHY).
chokes. Circular mixers are more broadband than double-bal-
MICROWAVE TRANSFORMER (see TRANS- anced mixers (several octaves bandwidth) and LO power is 5
FORMER). to 10 mW and a typical IF is 70 MHz. The typical mixer
based on Schottky-barrier diode performs signal conversion
MICROWAVE TRANSISTOR (see TRANSISTOR).
with a noise factor less than 10 dB in the frequency band 1 to
MICROWAVE TRANSMISSION LINE (see TRANS- 12 GHz.
MISSION LINE). The double circular mixer can be used to reduce conver-
sion losses due to recovery of image frequency power. It
MICROWAVE TRIODE (see TRIODE).
operated analogously to the double-balanced mixer and also
MIRROR, antenna (see ANTENNA, reflector). provides image frequency interference suppression. IAM
Ref.: Gassanov (1988), pp. 120, 122
MISSILE, antiradiation. An antiradiation missile is one
with a passive seeker, designed to destroy operating radars of A crystal mixer is one using the nonlinearity of the charac-
the adversary and guided by their emissions. The seeker teristic of a point-contact diode. The main shortcoming of this
includes an antenna system within a radome, a receiver, and a mixer is a big spread in parameters and low power handling