The wireless coverage cell on inside deployments can be extended with external antennas that plug into connectors on the access points. Most antennas can be mounted on the ceiling or wall and outside antennas often use a mast to increase height for line of sight.
Effective Isotropic Radiated Power = Transmit Power (dBm) + Gain (dB) - Cable Loss (dB)
Omni-Directional
Omni-directional antenna sends a horizontal radiated pattern of 360 degrees and a vertical pattern of 50 - 70 degrees from its source. From a practical perspective the pattern isn't circular as much as being elliptical. It is a multi-homing antenna that sends signals to several clients in proximity causing some multipath fading that is minimized with antenna diversity. The gain values with 2.4 GHz antenna range from 2.2 dBi - 12 dBi. The higher gain antenna is deployed outside for the most part. Some Cisco access points have an integrated omni-directional dipole antenna or " rubber ducky" that is standard with each device.
Directional
The directional antenna sends out a directed radiated pattern connecting with a distant antenna. The antenna purpose is to send traffic between antennas and not used for multi device homing. There are 3 specific directional antennas: Yagi, Patch and Dish. The Dish antenna has highest gain and narrowest radiation angle beam while Patch antenna has lowest gain and widest radiated beam. Gain values with 2.4 GHz antennas range from 6dBi - 21 dBi. Most antenna from this group are implemented in buildings with there is a lot of signal attenuation such as manufacturing, warehouses, and structures with a lot of steel, concrete, angled designs etc.
Diversity
The diversity antenna implement dual antenna on the access point receiving signals on both. The access point determines what antenna has best gain and transmits on that antenna. Diversity antennas are designed using either omni-directional, directional or dipole styles. Multipath fading occurs in buildings that have a lot of signal reflection. The signal finds multiple paths from source to destination and signal becomes distorted at receiver. This is minimized or eliminated with diversity antennas.
External Antenna
Some Cisco access points such as 1200 series have connectors available for an external antenna. This is available with deployments in environments where the access point is at a maximum 300 feet from the wired switch or signal distortion is excessive. The external antenna with a specified coax cable of 3 - 100 feet allow for placement of the antenna at optimal positioning. Minimizing the cable length will decrease signal attenuation before transmission. Implementing the higher gain diversity patch antenna fixes the problem of clients being out of range. The company could have deployed a repeater as an alternative solution with an 1100 series access point that doesn't support an external antenna.
Building material and structural design will contribute to signal attenuation. The following describes from best to worst building material used with walls, floors and ceilings. Steel and concrete with several feet of construction is most difficult.
• Wood• Concrete
• Reinforced Concrete
• Steel
3 comments:
I found that many of the homebrew antennas have a very poor performance, for example the famous pringles antenna. Others have a acceptable gain like the can antenna but even tunning with an spectrum analyser I couldn't get a better VSWR than 1.5:1.
Be aware that many of the commercial antennas are off frequency (checked with an spectrum analyzer) or have a poor gain or the radiation pattern is not as expected due to a poor impedance match.
I would suggest to make an antenna to the simpliest or to buy a well known antenna manufacturer.
This antenna is very similar than the ones embedded on laptops and is very easy to build:
Have a look in this website for some examples of good quality WiFi and Wimax antennas http://www.renair.co.uk
I think not all of homebrew antenna has a bad performance, pringles antenna does have a bad performance, but if you try other antenna like omni antenna homebrew, you must be impressed..
And if you want to put your website link, you can contact me via email.
thanks
admin
I have found one of a kind device that transform a N-Type antenna to 802.11 a,b,g 5.4 Ghz with a dbi of over 50 wish allows me to capture signal of over 5km alway for my home with a build in firmware wish allow to configure easier you can even use it with aircrack (ubnt bullet2 device) i think you guys should search google for the device bye bye home made antenna
www.wired-networks.blogspot.com
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