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Antenna Basics - Wi-LAN Inc 300-801 Manning Rd NE Calgary...

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Wi-LAN Inc . 300-801 Manning Rd. NE Calgary, Alberta, T2E 8J5 Phone: (403) 273-9133 Fax: (403) 273-5100 Page 1 of 5 Wi-LAN is the leader in wireless LAN technology Antenna Note Antennas focus and absorb radio energy in specific directions, depending on how they are designed. Antennas can be tuned to certain frequency ranges. Antennas used for Hopper Products must be “tuned” to 902-928 MHz or 2.4-2.5 GHz. Antenna Basics Gain Antennas have a gain associated with them, which is a measure of their ability to amplify signals in their tuned band. Antenna gain is achieved by focusing the signal. A higher gain antenna has a more compressed signal. dBd Versus dBi Antenna gain must be measured over a known reference and is often expressed as either dBd or dBi. dBd is antenna gain referenced over a half-wave dipole which is an antenna that has a donut shaped radiation pattern. dBi is antenna gain referenced over an isotropic radiator which is a theoretical antenna that radiates equally in all directions (ie. the sun). Wi-LAN references antenna gain in dBi. The conversion factor is: 0 dBd = 2.14 dBi Beamwidth The beamwidth of an antenna describes how a signal spreads out from the antenna as well as the range of the reception area. Beamwidth is measured between the points on the beam pattern at which the power density is half of the maximum power. This is often referred to as the -3 dB points. A high gain antenna has a very narrow beamwidth and may be more difficult to align. Downtilt or Uptilt Some antennas have either a downtilt or an uptilt associated with them. This is further focusing of the signal either in a downward or upward fashion with respect to the horizon. A tilt may either be electrically built into the antenna or achieved mechanically with the mounting gear. This may be necessary when there is a significant deviation in the elevation of the remote site(s) with respect to the base site. Front-to-Back Ratio (F/B) Directional antennas focus the signal in a forward path. This is achieved by directing the signal in one direction which in turn reduces the signal in the opposite direction.
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