. Compendium of meteorology. Meteorology. RADAR STORM OBSERVATION 1267 where / is a dimensionless factor which depends on the design and efficiency of the antenna and parabola (usually about or ).. Fig. 1.—Antenna parabolas of two of the radars used by the Weather Radar Research. The parabolic reflector to the left forms a conical beam of circular cross section. The one to the right (AN/TPS-lOA) forms a "beaver-tail" beam of elliptical cross section ° vertical and 2° horizontal. Both radars have an operating wave length of about 3 cm. ( Weather Radar Research.)
. Compendium of meteorology. Meteorology. RADAR STORM OBSERVATION 1267 where / is a dimensionless factor which depends on the design and efficiency of the antenna and parabola (usually about or ).. Fig. 1.—Antenna parabolas of two of the radars used by the Weather Radar Research. The parabolic reflector to the left forms a conical beam of circular cross section. The one to the right (AN/TPS-lOA) forms a "beaver-tail" beam of elliptical cross section ° vertical and 2° horizontal. Both radars have an operating wave length of about 3 cm. ( Weather Radar Research.) The antenna gain is a term used to express the in- crease of power resulting from the focusing of the radiated energy into a narrow beam, in contrast to isotropic radiation [49, pp. 18-21]. Microwave radar operates at such high frequencies in the radio spectrum that the radio energy may be focused by parabolic reflectors in a manner analogous to visible radiation focused by a searchlight. Directivity is desirable from the standpoint of target direction determination; energy conservation is necessary for maximum range of de- tection. The gain factor is dimensionless and may be loosely regarded as the ratio between the power density in the beam, resulting from focusing, and the power density which would exist at the same range if the trans- mitter radiated isotropically. Beam Width, 4> and 6. The beam width is usually defined as the angle subtended at the antenna between points across the beam where the power density is one- half that along the axis. When using this term it must be understood that an appreciable amount of power is actually present beyond this angle. However, the power beyond the half-power point decreases rapidly with increasing angle, so for most purposes this definition is probably sufficient. If the beam is circular in cross section, it may be depicted as a cone with the apex at the radar antenna. Cross-section figures of radar beams may be in a variet
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