A fan-beam antenna is a directional antenna producing the main beam having a narrow beamwidth in one dimension and a wider beamwidth in the other dimension. This pattern achieves by a truncated paraboloid reflector. Since the reflector is narrow in the vertical plane and wide in the horizontal, it produces a beam that is wide in the vertical plane and narrow in the horizontal.
Figure 2: A truncated paraboloid reflector
This type of antenna system is generally used in height-finding equipment (parabolic reflector cut-out rotated 90 degrees). Since the reflector is narrow in the horizontal plane and wide in the vertical, it produces a beam that is wide in the horizontal plane and narrow in the vertical. In shape, the beam of a height-finding radar is a horizontal fan beam pattern. In American publications, this type of antenna diagram is also described as a “beaver-tail diagram” or “beaver-tail pattern”, because it is flat and wide like a beavertail.
Figure 3: Heightfinder PRV-17 “Odd Group”
Figure 1: Fan-beam antennas pattern
a) lateral view
b) frontal view