horn antenna

an antenna consisting of a widening metal funnel—the horn—and a wave guide coupled to it. Horn antennas are used for the directional radiation and reception of radio waves in the superhigh-frequency range and as radiators for lens and reflector antennas; they are also used as self-contained antennas in communications satellites and in equipment used in measurement technology. The radiation pattern of a horn antenna depends on the character of the field strength distribution at the mouth (the largest cross section) of the horn, which, in turn, is determined by the shape of the inner and outer surfaces of the horn and by the horn’s geometric dimensions.

Figure 1. Types of horn antennas: (a) pyramidal, (b) sectoral, (c) conical, (d) horn with a parabolic generatrix; (1) wave guide, (2) horn

Horns are classified according to shape as pyramidal (Figure 1, a), sectoral (Figure 1, b), and conical (Figure l, c). Others are versions of these three basic types and include, for example, antennas with a generatrix in the form of a broken line or a smooth curve and antennas with a smooth or a corrugated inner surface. Various versions are used to improve one or another of the antenna’s electrical characteristics, for example, to obtain a radiation pattern that is axially symmetrical or has low power levels in the side lobes. In some cases, a delay or accelerating lens is placed at the mouth of a horn antenna in order to correct the antenna’s directional properties (seeLENS ANTENNA). For the best match between a horn antenna and its wave guide and between the antenna and free space, a matching section and tuning elements are sometimes provided, and the surface of the horn has a parabolic generatrix (Figure 1, d).