Page 188 - Radar Technology Encyclopedia

feed, four-horn feed, pillbox 178

A four-horn feed is a classical monopulse feed assembly and Table F1
network used in early monopulse radars. This feed is a cluster Monopulse Horn Feed Performance
of four horn feeds displaced about the focal point of a reflec-
tor or lens antenna. Each horn can be associated with a pencil
beam in space, squinted about the axis of the antenna
(Fig. F12). A basic problem in such antennas is the compro-
mise between sidelobe levels and efficiency in the sum and
difference patterns. More advanced feed systems use a
twelve-horn feed cluster or a multimode feed. SAL
Ref.: Barton (1988), p. 198.

(from Barton and Ward, 1969, p. 31).
A nutating feed is an offset feed that can rotate about the axis
of the dish in a reflector antenna and maintain the plane of
polarization fixed as it rotates. It is used in the technique of
conical scanning. SAL
Ref.: IEEE (1990), p. 22; Skolnik (1980), p. 155.
Figure F12 Beams formed with four-horn feed (from Rhodes,
optical feed (see space feed).
1980, p. 70).
An optical-fiber beam-forming circuit is a circuit that uses
A horn feed is a horn antenna used to illuminate a reflector or fiber-optic delay lines as the phase-shifting components.
lens. Radio signals from the output of each of the radiating ele-
Ref.: Silver (1949), p. 448; Sazonov (1988), p. 382. ments of the antenna array modulate the intensity of the
sources of optical radiation (lasers), and then the radiation is
A linear feed is a linear array of dipoles, horns, or waveguide
sent to the fiber-optic delay line. The length of the fibers
slots used to feed a parabolic cylinder reflector antenna.
forming the delay line, and thus the delay in each channel, is
Ref.: Silver (1949), pp. 13, 457; Sazonov (1988) p. 383.
selected so as to compensate for the output spatial delays of
Lopez feed (see dual-ladder feed). excitation of the radiating elements by the plane wave. Opti-
cal signals from the output of each fiber are delivered in par-
A monopulse feed is a feed network for a monopulse
allel, without interaction, to the phase-sensitive area of the
antenna. Typically, in a reflector or lens antenna system, horn
photodetector, adding the powers of the channels.
feeds are used with a network, which forms sum and differ-
Fiber-optic diagram-forming circuits are marked by their
ence channels. The main configurations in this case are two-
low size and mass parameters and energy consumption, and
horn (dual-mode and triple-mode), four-horn (simple and tri-
they have a high wideband capacity. IAM
ple-mode), and twelve-horn feeds. The shapes and typical
Ref.: Bratchikov, Radioelektronika 32, no. 2, 1989, p. 23; Zmuda (1994),
performance of monopulse feeds are given in Table F1.
p. 299.
In phased-array antennas using constrained feeds, the
parallel feed (see constrained feed).
monopulse feed network consists of a set of couplers that pro-
duce illumination functions having even and odd symmetry A parallel-plate feed is a reactive feed system using a micro-
about the center of the aperture; the former corresponding to wave structure to provide power division. Such feeds are
the sum channel and the latter the difference channels. SAL basically used with a linear array and have to be stacked to
Ref.: Barton (1988), pp. 198-206; Skolnik (1990), p. 6.21. feed a planar array. The parallel-plate horn and pillbox feed
are examples. SAL
A multiple-beam feed is used in a multiple-beam antenna to
generate multiple simultaneous beams covering, for example, Ref.: Skolnik (1980), p. 309.
the elevation sector of a 3D surveillance radar. The main A pillbox feed is a pillbox antenna used as a feed; for exam-
types of multiple-beam feeds are monopulse feeds and multi- ple, to illuminate a linear array (Fig. F13). If the array of
ple-beam-forming networks. (See Blass feed, Butler feed, pickup elements is matched to the pillbox then no reflections
monopulse feed.) SAL occur, and if the back surface of the pillbox is made spherical
Ref.: Johnson (1984), p. 20.56. instead of parabolic, the feed can provide many multiple-
simultaneous beams with the use of multiple feed horns. SAL
Ref.: Johnson (1984), p. 20.56.