period of the wave. A linear polarized antenna may be either
Horizontally Polarized
(if the direction of propagation is parallel
to the earth’s surface) or
Vertically Polarized
(if the direction
of propagation is perpendicular to the earth’s surface). A
circular polarized antenna may be either Right-Hand-Circular
(
RHC
) or Left-Hand-Circular (
LHC
) depending on whether the
direction of rotation of the plane of propagation is clockwise
or counterclockwise respectively. Polarization is an important
design consideration, particularly in Line of Sight (LOS) or
Point-to-Point type deployments because maximum signal
strength between sending and receiving antennas occurs when
both are using identical polarization.
Radiation Pattern
of an antenna is a plot of the relative strength
of the electromagnetic field of the radio waves emitted by the
antenna at different angles. Radiation patterns are typically
represented by either a three-dimensional graph or by a set of
two separate two-dimensional polar plots of the horizontal and
vertical cross sections. The radiation pattern of the theoretical
isotropic antenna, which radiates equally in all directions, would
look like a sphere.
Impedance Matching
is an important consideration in the
design of the overall wireless communication system. This is
because an electromagnetic wave traveling through various
parts of a communication system (radio, cable, connectors, air)
may encounter differences in impedance. At each interface,
depending on the impedance mismatch, some fraction of
the propagating radio wave’s energy will reflect back into the
source. This reflecting wave is called a standing wave and the
ratio of maximum power to minimum power in the standing
wave is called the
Voltage Standing Wave Ratio
(
VSWR
). A VSWR
of 1:1 is ideal.
Types of Xirrus Antennas
The tables starting on the next page detail the specifications
of the different antennas Xirrus offers for use with its Arrays
and Access Points, in both 2.4GHz and 5GHz. Each type of
antenna will offer certain coverage capabilities suited for specific
applications (as discussed in the later section of this document).
The radiation patterns listed below also provide some guidance
on the coverage to be expected from a given antenna. As a
general rule of thumb as the gain of an antenna increases, there
is some tradeoff to its coverage area. High gain antennas will
typically offer longer coverage distance but smaller (and more
directed) coverage area.
Содержание "Rubber Duck" Antenna
Страница 1: ...EXTERNAL ANTENNA GUIDE REFERENCE GUIDE ...
