User's Manual

Page 10 of 11 6/17/2003
Antenna polarity
Antenna polarization refers to the direction in which the electromagnetic field lines point as energy
radiates away from the antenna. In general, the polarization is elliptical. The simplest and most common
form of this elliptical polarization is a straight line, or linear polarization. Of the transmitted power that
reaches the receiving antenna, only the portion that has the same polarization as the receiving antenna
polarization is actually received. For example, if the transmitting antenna polarization is pointed in the
vertical direction (vertical polarization, for short), and the receiving antenna also has vertical polarization,
the maximum amount of power possible will be received. On the other hand, if the transmit antenna has
vertical polarization and the receiving antenna has horizontal polarization, no power should be received. If
the two antennas have linear polarizations oriented at 45° to each other, half of the possible maximum
power will be received.
Antenna Types
Whip antenna
You can use a 1/2λ straight whip or 1/2λ articulating whip (2 dBi) antenna with OS2400-HSE radios. These
antennas are the most common type in use today. Such antennas are approximately 5 inches long, and are
likely to be connected to a client radio (connected directly to the radio enclosure). These antennas do not
require a ground plane. Articulating antennas and non-articulating antennas work in the same way. An
articulating antenna bends at the connection.
Collinear array antenna
A collinear array antenna (shown at left) is typically composed of several linear antennas stacked
on top of each other. The more stacked elements it has, the longer it is, and the more gain it has.
It is fed in on one end.
The antenna pattern is torroidal. Its azimuthal beam width is 360° (omnidirectional). Its vertical
beam width depends on the number of elements/length, where more elements equal narrower
beam width. The antenna gain also depends on the number of elements/length, where more
elements produce higher gain. Typical gain is 5 to 10 dBi.
The antenna polarity is linear, or parallel to the length of the antenna.
Yagi array antenna
A yagi antenna is composed of an array of linear elements, each parallel to one another and attached
perpendicular to and along the length of a metal boom. The feed is attached to only one of the elements.