User's Manual

Page 11 of 11 6/17/2003
Elements on one side of the fed element are longer and act as reflectors; elements on the other side are
shorter and act as directors. This causes the antenna pattern to radiate in a beam pointed along the
boom toward the end with the shorter elements. The pattern and beam width depend on the overall
antenna geometry, including the number of elements, element spacing, and element length, but they are
generally proportional to the length, where longer length produces a narrower beam. Sometimes the
antenna is enclosed in a protective tube that hides the actual antenna geometry.
The antenna gain also varies with antenna geometry, but generally is proportional to the length, where
longer length produces higher gain. Typical values are 6 to 15 dBi. The antenna polarity is linear (parallel
to the elements, perpendicular to the boom).
Parabolic reflector antenna
A parabolic reflector antenna consists of a parabolic shaped dish and a
feed antenna located in front of the dish. Power is radiated from the feed
antenna toward the reflector.
Due to the parabolic shape, the reflector concentrates the radiation into a
narrow pattern, resulting in a high-gain beam.
The antenna pattern is a beam pointed away from the concave side of the
dish. Beam width and antenna gain vary with the size of the reflector and
the antenna construction. Typical gain values are 15 to 30 dBi.
The antenna polarity depends on the feed antenna polarization.