Page 45 - Radar Technology Encyclopedia

antenna, low-sidelobe antenna, multiple-reflector 35

Among reflector antennas the parabolic cylinder with when the antenna is mounted on an aircraft. The main disad-
line feed (Fig. A68) and the doubly-curved reflector with vantage is narrowbandness associated with the resonant mode
complex feed give reasonable compromises between effi- of antenna operation. Sometimes these antennas are termed
ciency and low sidelobe level. As to phased arrays, the most printed-circuit or patch antennas. AIL
promising ULSA technique is the electrically fixed array of Ref.: Gupta (1988); Bhartia (1991); Johnson (1993), Ch. 7; Sazonov (1988),
slotted waveguides. In electronically scanned arrays, anten- p. 258; Zurcher (1995), Ch. 2; Sainati (1996).
nas with digital beam forming (DBF) offer low-sidelobe per- Mill’s cross antenna (see ARRAY, Mill’s cross).
formance for receiving. SAL
A minimum scattering antenna is a lossless antenna, fed
Ref.: Brookner (1988), Ch. 6; Barton (1988), pp. 188–196; Skolnik (1990),
pp. 7.37–7.49; Farina (1992), pp. 13–58. from an N-port matched and uncoupled waveguide system,
that is rendered invisible when all the ports are terminated in
open circuits. This concept is used in antenna radar cross sec-
tion reduction techniques. SAL
Ref.: Knott (1985), p. 416.
mirror antenna (see reflector antenna).
An antennamitter is an antenna with an embedded
transmitter.
An antennamixer is an antenna with an embedded mixer.
A monopulse antenna is one forming the patterns appropri-
ate for monopulse angle-sensing and -tracking. The antenna
system for conventional monopulse radar must form three
simultaneous patterns: a sum beam, a difference beam for azi-
muth and a difference beam for elevation. Typically, reflector
antennas, phased arrays, lens antennas, and spiral antennas
are used. Monopulse patterns are formed using four-horn or
multiple-horn feeds for reflector antennas or space-fed arrays,
and dual-ladder feeds for constrained feed arrays. SAL
Ref.: Leonov (1986), p. 13; Johnston (1984), p. 19.10; Johnson (1993),
Figure A68 Low-sidelobe antenna using line-fed parabolic Ch. 34; Barton (1988), pp. 198–204.
cylinder.
A multielement antenna is one comprising several elements.
antenna measurement (see TEST, antenna). The main types are antenna arrays and traveling-wave anten-
nas. Various types of multielement antennas are widely used
A microstrip antenna is one manufactured with printed-cir-
in radar since they can provide a high directive gain and a
cuit technology. The main constituent parts of a microstrip
narrow beamwidth in conjunction with excellent capabilities
antenna (Fig. A69) are a metal radiator, a ground plane, and
for adaptation to interference environments. AIL
the dielectric substrate. Excitation is by the coaxial line
Ref.: Bakhrakh (1989), p. 11.
through the hole on the ground plane and substrate, as shown
in the figure, or by a strip line in the plane of the radiator. The A multiple-beam antenna is one forming a series of beams
main advantages of such antenna are the simplicity, relatively simultaneously. The main types of multibeam antennas are
small volume and weight, and small aerodynamic resistance stacked-beam antennas and monopulse antennas based on
reflector antenna or space-fed array techniques, illuminated
z by multiple-horn feed clusters or array feeds. SAL
Ref.: Johnson (1993), pp. 17.41–17.52; Barton (1988), pp. 196–207.
A multiple-reflector antenna is one using additional second-
L ary reflectors (subreflectors) to form the antenna pattern. The
secondary reflector makes it possible to relocate the feed
y
close to the source or receiver, to produce low spillover, to
produce a low-sidelobe distribution, and to provide other
advantages. If only one additional subreflector is used, the
term dual-reflector antenna is used. The most common multi-
h ple-reflector antenna in radar applications is the Cassegrai-
x
nian type. SAL
Input
Ref.: Skolnik (1990), pp. 6.23–6.25; Johnson (1993), pp. 17.33–17.44.
Figure A69 Microstrip antenna.