Technical data

108 Theoretical and general applications www.westermo.com
Types of antennas
Dipoles and dipole arrays are constructed of one or multiple dipole antennas and
power splitters combining the antennas. These are typically omni-
directional or off-set pattern antennas.
Yagi and Yagi arrays are constructed of one or multiple yagi antennas
and power splitters combining the antennas. These are always direc-
tional antennas. Cross-polarized yagis are a combination of two inde-
pendently fed, orthogonally polarized and physically quarter wave
phased yagi antennas on the same boom. Cross-polarized yagis are used in applica-
tions where polarization diversity is required or in a circular polarization mode when
two yagi antennas are combined with a power splitter.
Omni-directionals can be either end fed half wave antennas, collinear antennas or
ground plane antennas. These antennas radiate in all directions equally.
Portables are typically flexible quarter wave antennas with specific feeding methods
for proper impedance match with small sized portable radio equipment.
Signal propagation
Radio waves propagate mainly along line of the sight but there will also be bending,
reflection and diffraction occurring. Typically, radio waves propagate simultaneously in
many different modes and paths. This multi-path propagation causes some signal insta-
bility as a function of time due to the summing of multiple incoming signals, which have
different phases. This also explains why a small physical movement of the antenna can
have influence on indicated signal strength.
The radio horizon is about 15% further than the optical horizon due to radio waves
tendency to bend.
Example of
Yagi aerial
Example of
Dipole aerial
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