Advertisement
Antenna Polarity
Polarization refers to the orientation of the electric field component of an electromagnetic wave with respect to the
Earth's surface. An electromagnetic wave is composed of electric and magnetic fields propagating perpendicular to each
other. Radio and light are examples of electromagnetic waves. Electromagnetic waves can propagate with linear, circular
or elliptical polarization. Linear polarization is the most popular method used in WiFi communications and can take two
forms, vertical and horizontal. Polarity must be observed on both ends of a communication link. A properly designed
antenna will offer 20 dB or more of isolation between the two polarities.
Dual Polarized Antennas
A dual polarized antenna uses extra internal elements to provide two polarities in a single package via separate input
ports. For a linear design both vertical and horizontal polarities are available. For a circular design both right hand
circular polarity (RHCP) and left hand circular polarity (LHCP) are available. The isolation between the two ports allows
the antenna to transmit or receive two signals on the same frequency simultaneously. Dual polarity antennas have
multiple uses. In outdoor 802.11n multiple input-multiple output (MIMO) systems, the isolation allows the two MIMO
streams to coexist without interference. For indoor 802.11g systems, polarization or spatial diversity can counteract the
effects of multipath and fading. In DBS home satellite systems, polarization is used to allow twice the amount of
transponders to be installed on a satellite.
Antenna Frequency
Antennas operate at different frequencies to suit different applications. The antennas frequency must match the
frequency of the amplifier, access point, or router it will be attached to in order for the system to work. In the US the
900, 2400 and 5000 MHz frequency bands are set aside by the FCC for unlicensed Industrial, Scientific and Medical (ISM)
applications. The lack of licensing requirements has greatly encouraged the growth of the wireless industry. These bands
are used for consumer and commercial WiFi and WLAN applications as well as for commercial Radio Frequency
Identification (RFID) and Supervisory Control and Data Acquisition (SCADA) applications. For the consumer the 2.4 GHz
band is the primary band one uses for WiFi, Bluetooth, cordless phone, printer, keyboard, mouse and gaming controller
applications. Cellular use licensed bands spread over the 700 – 2700 MHz range.
© L -com, Inc. A ll R ights R eserved. L -com Connectivity Products and the L -com L ogo are registered marks.
T oll Free Ordering and T echnical Support: 1-800-343-1455 V isit our website at
www.L -com.com
4
Advertisement
