The
selection and installation of access point antenna supplies influence network
performance and accessibility. The signal strength or amount of energy radiated
from an antenna must do with antenna type and access point transmit
specifications. Cable length will boost signal attenuation or reduction and
should be minimized. Each antenna kind is going to have vertical and horizontal
beamwidth defined. The antenna type, gain, cable length, number, and mounting
are all key to the design. For example, a directional antenna with high gain, no
outside cable, mounted at the proper height will give the best performance in an
outside deployment with a lot of interference.
The
wireless policy cell on interior deployments may be extended using external
antennas that plug into connectors on the access points. Most antennas can be
mounted on the ceiling or wall and outside antennas frequently use a mast to
increase height for line of sight.
Omni-Directional
Omni-directional
antenna directs a flat radiated pattern of 360 degrees and a vertical design 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 many customers in proximity inducing some multipath fading that's
diminished with antenna diversity. 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 every device.
Directional
The directional antenna sends out a directed radiated pattern connecting with a
remote antenna. The antenna's purpose is to send traffic between antennas rather
than used for multipurpose device homing. There are 3 unique directional
antennas: Yagi, Patch, and Dish. The Dish antenna has got maximum gain and
narrowest radiation angle beam while the Patch antenna has the lowest gain and widest
radiated beam. Gains with 2.4 GHz antennas range from 6dBi - 21 dBi. Most
antennas from this collection are employed in buildings with a lot of signal
attenuation such as manufacturing, warehouses, and structures with a lot of
steel, concrete, angled designs, etc..
Diversity
The
diversity antenna implements dual antennas on the access point receiving
signals on both. The access point decides what antenna has the best gain and
transmits on this antenna. Diversity antennas are made 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 origin to destination and the signal becomes distorted at the
recipient. This is minimized or removed with diversity antennas.
External Antenna
Some
Cisco access points, for example, 1200 strings, have connectors available for an
outside antenna. This can be found with deployments in environments where the
access point is in a maximum 300 feet in the wired switch or signal distortion
is excessive. The outside antenna with a given coax cable of 3 - 100 feet
allows for placement of the antenna at optimum positioning. Minimizing the
cable length will reduce signal attenuation before transmission. Implementing
the higher gain diversity patch antenna fixes the problem of clients being out
of scope. The business could have deployed a repeater as an alternative solution
using an 1100 series access point that doesn't support an external antenna.
External wireless antennas
can be used to find more networks to connect to, penetration testing, extending
outdoor wireless networks, security testing for site surveys, and overall just
looking cool.
Another type of external antenna can be used to extend your wireless router or wireless access point.
Adding the proper antenna to your wireless access point will make your LAN
perform like it is on crack. If you really want to extend your range you will
have to add an external wireless antenna on your wireless access point and your
laptop. Remember that wireless LAN communication is not like an AM/FM radio,
you need to be able to hear and talk. If you have a huge antenna and amplifier
on one end you need almost the same setup on the other end to talk back.
Building
material and structural design will lead to signal attenuation. The following
describes from best to worst building material utilized with walls, ceilings
and floors. Steel and concrete with different feet of the structure are the most
difficult.
*
Wood
*
Reinforced Concrete
Access
points should be ceiling mounted when possible at least 17 - 19 feet in
elevation optimizing vertical and horizontal beamwidth. In some cases, the
access points will have to be mounted on the wall. Antenna mounting is
significant and needs to be implemented with instructions from the hardware
installation guide. The Cisco access points utilize the standard RP-TNC 50-ohm
type connector.
Outside Bridge rotational
Companies
have implemented a lot of Cisco wireless bridges that connect buildings in a
campus community. The line of sight must be accessible or use a repeater bridge
to extend the network where it is not available. Outside antennas deal with
ecological issues and more distances which need higher gain directional
antennas. Mounting is usually with a mast or flat against a wall. Distances can
expand around 250 - 500 ft or much further with greater wattage bridges, proper
mounting of the antenna, and deploying repeaters. Point to multipoint topology is
executed equally with inside and outside wireless deployments. The main bridge
or root access point in a multipoint topology is homed with visitors from
several non-root bridges or access points. That topology is implemented with
several talked buildings and a heart or core office that must be networked
outside. The spoke offices have a point to point link with the hub office and
the heart office has a multipoint relationship with all spoke offices. The hub
office will apply an omnidirectional antenna with a lot of beam width while
talked offices will utilize a directional antenna.
Antenna Mounting
The
interior standard access point layouts will not have a set of directional
antennas. Most will employ Omni-directional antennas and use directional
antennas where necessary as a means of addressing distances. The outside
implementations for the most part imply larger distances and environmental
concerns making directional antennas an effective choice.
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