RF Signal and Antenna
Dr. Tahseen Al-Doori
Objectives
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Active and Passive Gain
Azimuth and Elevation Chart
Beamwidth
Antenna Types
Visual line of sight
RF line of sight
Fresnel Zone
Dr. Tahseen Al-Doori
 Antenna Polarization
 Antenna Diversity
 Multi-Input-Multi-Output (MIMO)
Dr. Tahseen Al-Doori
 The installation of antennas has the greatest
ability to affect whether the communication
is successful or not.
 Antenna installation can be as easy as
placing an access point in your office or it
can be as complex as installing an
assortment of directional antennas.
 With the proper understanding of antennas
and how they function, successful planning
for and installing them in a wireless network
will become a skillful and rewarding task.
Dr. Tahseen Al-Doori
Active and Passive Gain
 You can increase the signal that is radiated
out of the antenna (EIRP), by increasing the
output of the transmitter, which in turn
increase the amount of power provided by
the antenna (Intentional Radiator) and thus
the amount of power from the antenna
(EIRP).
 This increase is referred to as Active Gain.
Dr. Tahseen Al-Doori
 When power is focused, the amount provided to
the antenna does not change. It is the antenna
acting like a lens on a flashlight that increase the
power output by concentrating the RF signal in a
specific direction.
 Since the gain was created by shaping or directing
the signal, and not by increasing the overall
power, this increase is referred to as Passive gain.
 Passive gain is caused by focusing the existing
power, while the active gain is caused by adding
more power.
Dr. Tahseen Al-Doori
Azimuth and Elevation Chart
 There are many antenna types designed for
many different purposes, just as there are
many types of lights designed for many
purposes.
 It is easy to see the different lights by
lighting them on, unfortunately, in the case
of antennas that is not the case.
Dr. Tahseen Al-Doori
 With the antenna measurements you need
to walk around the antenna with an RF
meter, take measurements and then plot it
on piece of paper to find out the behavior of
the RF Signal. This is a time consuming task
and the results will be affected by the
interference of many objects. Therefore, the
manufacturers create azimuth charts and
elevation charts. Which is known as
radiation patterns.
Dr. Tahseen Al-Doori
Azimuth and elevation charts
Dr. Tahseen Al-Doori
Here are a few statements that will help you
interpret the radiation charts:
 In either chart, the antenna is placed at the
middle of the chart.
 Azimuth chart = H-plane = top-down view
 Elevation chart = E-plane = side view
The outer ring of the chart usually represents
the strongest signal of the antenna. The
chart does not represent distance or any
level of power or strength. It only represents
the relationship of power between different
points on the chart.
Dr. Tahseen Al-Doori
 One way to think of the chart is to consider the
way a shadow behaves.
 If you were to move a flashlight closer or farther
from your hand, the shadow of your hand would
grow larger or smaller. The size of the shadow
does not represent the size of the hand. The
shadow only shows the relationship between the
hand and the fingers.
 With an antenna, the radiation pattern will grow
larger or smaller depending upon how much
power the antenna receives, but the shape and
the relationships represented by the patterns will
always stay the same.
Dr. Tahseen Al-Doori
Beamwidth
 Is the measurement of how broad or narrow the
focus of an antenna is and is measured both
horizontally and vertically.
 It is the measurement from the center, or strongest
point, of the antenna signal to each of the points
along the horizontal and vertical axes where the
signal decreases by half power (–3 dB), as seen in
the Fig. below
Dr. Tahseen Al-Doori
 These –3 dB points are often referred to as
half power points. The distance between the
two half power points on the horizontal axis
is measured in degrees, giving the
horizontal beamwidth measurement. The
distance between the two half power points
on the vertical axis is also measured in
degrees, giving the vertical beamwidth
measurement.
Dr. Tahseen Al-Doori
Antenna Types
There are three main categories of antennas:
 Omni-directional: radiate RF in a fashion similar
to the way a table or floor lamp radiates light. They
are designed to provide general coverage in all
directions.
 The small rubber dipole antenna, often referred
to as a “rubber duck” antenna, is the classic
example of an omni-directional antenna and is the
default antenna of most access points.
 The closest thing to an isotropic radiator is the
omni-directional dipole antenna.
Dr. Tahseen Al-Doori
 An easy way to explain the radiation pattern of a
typical omni-directional antenna is to hold your
index finger straight up (this represents the
antenna) and place a donut on it as if it were a ring
(this represents the RF signal).
 If you were to slice the Donut in half horizontally,
as if you were planning to spread butter on it, the
cut surface of the Donut would represent the
azimuth chart, or H-plane, of the omni-directional
antenna. If you took another Donut and sliced it
vertically instead, essentially cutting the hole that
you are looking through in half, the cut surface of
the Donut would now represent the elevation, or
E-plane, of the omni-directional antenna.
Dr. Tahseen Al-Doori
 We have learned that antennas can focus or
direct the signal that they are transmitting.
 It is important to know that the higher the
dBi or dBd value of an antenna, the more
focused the signal.
 When discussing omni-directional antennas,
it is not uncommon to initially question how it
is possible to focus a signal that is radiated
in all directions.
 With higher-gain omni-directional antennas,
the vertical signal is decreased and the
horizontal power is increased.
Dr. Tahseen Al-Doori
 The Fig. below shows the elevation view of three
theoretical antennas. Notice that the signal of the
higher-gain antennas is elongated, or more
focused horizontally. The horizontal beamwidth of
omni-directional antennas is always 360 degrees,
and the vertical beamwidth ranges from 7 to 80
degrees, depending upon the particular antenna.
Dr. Tahseen Al-Doori
 Because of the narrower vertical coverage of the
higher-gain omni-directional antennas, it is
important to carefully plan how they are used.
Placing one of these higher-gain antennas on the
first floor of a building may provide good coverage
to the first floor, but because of the narrow vertical
coverage, the second and third floors may receive
minimal signal.
 In some installations you may want this; in others
you may not. Indoor installations typically use lowgain omni-directional antennas with gain of about
2.14 dBi.
Dr. Tahseen Al-Doori
 Antennas are most effective when the length
of the element is an even fraction (such as
1/4 or 1/2) or a multiple of the wavelength
(λ).
 A 2.4 GHz half-wave dipole antenna
consists of two elements, each 1/4λ in
length (about 1 inch), running in the
opposite direction from each other.
Dr. Tahseen Al-Doori
 Omni-directional antennas are typically used
in point-to-multipoint environments.
 The omni-directional antenna is connected
to a device (such as an access point) that is
placed at the center of a group of client
devices, providing central communications
capabilities to the surrounding clients.
 High-gain omni-directional antennas can
also be used outdoors to connect multiple
buildings together in a point-to-multipoint
configuration.
Dr. Tahseen Al-Doori
 A central building would have an omnidirectional antenna on its roof, and the
surrounding buildings would have directional
antennas aimed at the central building. In
this configuration, it is important to make
sure that the gain of the omni-directional
antenna is high enough to provide the
coverage necessary but not so high that the
vertical beamwidth is too narrow to provide
an adequate signal to the surrounding
buildings.
Dr. Tahseen Al-Doori
 The Fig. below shows an installation where
the gain is too high. The building to the left
will be able to communicate, but the building
on the right is likely to have problems.
Dr. Tahseen Al-Doori
 Semi-directional: radiate RF in a fashion
similar to the way a wall sconce is designed
to radiate light away from the wall or the way
a street lamp is designed to shine light down
on a street or a parking lot, providing a
directional light across a large area.
 Semi-directional antennas are used for
short- to medium-distance communications,
with long-distance communications being
served by highly-directional antennas
Dr. Tahseen Al-Doori
There are three types of antennas that fit into
the semi-directional category:
 Patch
 Panel
 Yagi (pronounced “YAH-gee”)
 Patch and panel antennas are more
accurately classified or referred to as planar
antennas.
Dr. Tahseen Al-Doori
The exterior of a patch antenna and the
internal antenna element
Dr. Tahseen Al-Doori
 These antennas can be used for outdoor
point-to-point communications up to about a
mile but are more commonly used as a
central device for indoor point-to-multipoint
communications.
 It is common for patch or panel antennas to
be connected to access points to provide
directional coverage within a building.
 Planar antennas can be used effectively in
libraries, warehouses, and retail stores with
long aisles of shelves.
Dr. Tahseen Al-Doori
 Due to the tall, long shelves, omni-directional
antennas often have difficulty providing RF
coverage effectively.
 In contrast, planar antennas can be placed high on
the side walls of the building, aiming through the
rows of shelves.
 The antennas can be alternated between rows
with every other antenna being placed on the
opposite wall. Since planar antennas have a
horizontal beamwidth of 180 degrees or less, a
minimal amount of signal will radiate outside of the
building. With the antenna placement alternated
and aimed from opposite sides of the building, the
RF signal is more likely to radiate down the rows,
providing the necessary coverage.
Dr. Tahseen Al-Doori
 Planar antennas are also often used to provide
coverage for long hallways with offices on each
side or hospital corridors with patient rooms on
each side.
 A planar antenna can be placed at the end of the
hall and aimed down the corridor. A single planar
antenna can provide RF signal to some or all of
the corridor and the rooms on each side and some
coverage to the floors above and below.
 How much coverage will depend upon the power
of the transmitter, the gain and beamwidth (both
horizontal and vertical) of the antenna, and the
attenuation properties of the building.
Dr. Tahseen Al-Doori
 Using semi-directional antennas indoors
often reduces reflections, thus minimizing
some of the negative effects of multipath
such as data corruption.
Dr. Tahseen Al-Doori
 Yagi antennas are not as unusual as they
sound.
 The traditional television antenna that is
attached to the roof of a house or apartment
is a yagi antenna. The television antenna
looks quite different because it is designed
to receive signals of many different
frequencies (different channels) and the
length of the elements vary according to the
wavelength of the different frequencies.
Dr. Tahseen Al-Doori
 A yagi antenna that is used for 802.11
communications is designed to support a
very narrow range of frequencies, so the
elements are all about the same length.
 Yagi antennas are commonly used for shortto medium-distance point-to-point
communications of up to about 2 miles,
although high-gain yagi antennas can be
used for longer distances.
Dr. Tahseen Al-Doori
The exterior of a yagi antenna and the internal
antenna element
Dr. Tahseen Al-Doori
 Another benefit of semi-directional antennas
is that they can be installed high on a wall
and tilted downward toward the area to be
covered.
 This cannot be done with an omnidirectional antenna without causing the
signal on the other side of the antenna to be
tilted upward. Since the only RF signal that
radiates from the back of a semi-directional
antenna is incidental, the ability to aim it
vertically is an additional benefit.
Dr. Tahseen Al-Doori
 Highly directional: radiate RF in a fashion
similar to the way a spotlight is designed to
focus light on a flag or a sign. Each type of
antenna is designed with a different
objective in mind.
 Highly-directional antennas are strictly used
for point-to-point communications, typically
to provide network bridging between two
buildings. They provide the most focused,
narrow beamwidth of any of the antenna
types.
Dr. Tahseen Al-Doori
There are two types of highly-directional antennas:
 Parabolic dish and grid antennas.
 The parabolic dish antenna is similar in
appearance to the small digital satellite TV
antennas that can be seen on the roofs of many
houses.
 The grid antenna resembles the rectangular grill of
a barbecue, with the edges slightly curved inward.
The spacing of the wires on a grid antenna is
determined by the wavelength of the frequencies
that the antenna is designed for.
Dr. Tahseen Al-Doori
 Because of the high gain of highly-directional
antennas, they are ideal for long-distance
communications as far as 35 miles (58 km). Due
to the long distances and narrow beamwidth,
highly-directional antennas are affected more by
antenna wind loading, which is antenna movement
or shifting caused by wind. Even slight movement
of a highly-directional antenna can cause the RF
beam to be aimed away from the receiving
antenna, interrupting the communications. In highwind environments, grid antennas, due to the
spacing between the wires, are less susceptible to
wind load and may be a better choice.
Dr. Tahseen Al-Doori
 Another option in high-wind environments is
to choose an antenna with a wider
beamwidth.
 In this situation, if the antenna were to shift
slightly, due to its wider coverage area, the
signal would still be received. No matter
which type of antenna is installed, the
quality of the mount and antenna will have a
huge effect in reducing wind load.
Dr. Tahseen Al-Doori
Phased Array
 A phased array antenna is actually an antenna
system and is made up of multiple antennas that
are connected to a signal processor.
 The processor feeds the individual antennas with
signals of different relative phases, creating a
directed beam of RF signal aimed at the client
device.
 Because it is capable of creating narrow beams, it
is also able to transmit multiple beams to multiple
users simultaneously. Phased array antennas do
not behave like other antennas since they can
transmit multiple signals at the same time.
Because of this unique capability, they are often
regulated differently by the local RF regulatory
agency.
Dr. Tahseen Al-Doori
Sector Antennas
 Sector antennas are a special type of high-gain,
semi-directional antennas that provide a pieshaped coverage pattern.
 These antennas are typically installed in the
middle of the area where RF coverage is desired
and placed back to back with other sector
antennas. Individually, each antenna services its
own piece of the pie, but as a group, all of the pie
pieces fit together and provide omni-directional
coverage for the entire area.
Dr. Tahseen Al-Doori
 Unlike other semi-directional antennas, a
sector antenna generates very little RF
signal behind the antenna (back lobe) and
therefore does not interfere with the other
sector antennas that it is working with.
 The horizontal beamwidth of a sector
antenna is from 60 to 180 degrees, with a
narrow vertical beamwidth of from 7 to 17
degrees.
 Sector antennas typically have a gain of at
least 10 dBi.
Dr. Tahseen Al-Doori
 Installing a group of sector antennas to provide
omni-directional coverage for an area provides
many benefits over installing a single omnidirectional antenna.
 To begin with, sector antennas can be mounted
high over the terrain and tilted slightly downward,
with the tilt of each antenna at an angle
appropriate for the terrain it is covering. Omnidirectional antennas can also be mounted high
over the terrain; however, if an omni-directional
antenna is tilted downward on one side, the other
side will be tilted upward.
Dr. Tahseen Al-Doori
 Since each antenna covers a separate area, each
antenna can be connected to a separate
transceiver and can transmit and receive
independently of the other antennas.
 This would provide the capability for all of the
antennas to be transmitting at the same time,
providing much greater throughput.
 A single omni-directional antenna would be
capable of transmitting to only one device at a
time.
 The last benefit of the sector antennas over a
single omni-directional antenna is that the gain of
the sector antennas is much greater than the gain
of the omni-directional antenna, providing a much
larger coverage area.
Dr. Tahseen Al-Doori
 Sector antennas are used extensively for
cellular telephone communications and are
starting to be used for 802.11 networking.
 Example: As you walk or drive around your
town or city, look for radio communications
towers that are around your neighborhood.
Many of these towers have what appear to
be rings of antennas around them. These
rings of antennas are sector antennas. If a
tower has more than one grouping or ring
around it, then there are multiple cellular
carriers using the same tower.
Dr. Tahseen Al-Doori
Visual Line of Sight
 When light travels from one point to another, it travels
across what is perceived to be an unobstructed straight
line, known as visual line of sight (LOS).
 For all intents and purposes, it is a straight line, but due to
the possibility of light refraction, diffraction, and reflection,
there is a slight chance that it is not. If you have been
outside on a summer day and looked across a hot parking
lot at a stationary object, you may have noticed that
because of the heat rising from the pavement, the object
that you were looking at seemed to be moving. This is an
example of how visual LOS is sometimes altered slightly.
 When it comes to RF communications, visual LOS has no
bearing on whether the RF transmission is successful or
not.
Dr. Tahseen Al-Doori
RF Line of Sight
 Point-to-point RF communication also needs to
have an unobstructed line of sight between the
two antennas.
 So the first step for installing a point-to-point
system is to make sure that from the installation
point of one of the antennas, you can see the
other antenna.
 Unfortunately, for RF communications to work
properly, this is not sufficient. An additional area
around the visual LOS needs to remain clear of
obstacles and obstructions.
 This area around the visual LOS is known as the
Fresnel zone and is often referred to as RF line of
sight.
Dr. Tahseen Al-Doori
Fresnel Zone
 The Fresnel zone (pronounced “FRUH-nel”;
the s is silent) is an imaginary Rugby ballshaped area that surrounds the path of the
visual LOS between two point-to-point
antennas. The fig. shows an illustration of
the Fresnel zone’s rugby ball-like shape.
Dr. Tahseen Al-Doori
 Theoretically, there are an infinite number of
Fresnel zone’s. The closest ellipsoid is
known as the first Fresnel zone, the next
one is the second Fresnel zone, and so on.
 For simplicity’s sake, and since they are the
most relevant for this section, only the first
two Fresnel zones are displayed in the
figure. The subsequent Fresnel zones have
very little effect on the communications.
Dr. Tahseen Al-Doori
 The fig. below illustrates a link that is 1 mile
long. The top solid line is a straight line from
the center of one antenna to the other. The
dotted line shows 60 percent of the bottom
half of the Fresnel zone. The bottom solid
line shows the bottom half of the first
Fresnel zone. The trees are potential
obstructions along the path.
Dr. Tahseen Al-Doori
 The typical obstacles that you are likely to
encounter are trees and buildings.
 It is important to periodically visually check your
link to make sure that trees have not grown into
the Fresnel zone or that buildings have not been
constructed that encroach into the Fresnel zone.
Do not forget that the Fresnel zone exists below,
to the sides, and above the visual LOS. If the
Fresnel zone does become obstructed, you will
need to either move the antenna (usually raise it)
or remove the obstacle.
Dr. Tahseen Al-Doori
 To determine if an obstacle is encroaching
into the Fresnel, you will need to learn a few
formulas that will allow you to calculate its
radius.
 We are only concerned with the following
formula as it calculate the radius of the first
Fresnel zone at the mid-point between the
two antennas. This is the point where the
Fresnel zone is the largest. This formula is
as follows:
Dr. Tahseen Al-Doori
N = which Fresnel Zone you are calculating
(usually 1 or 2)
d1 = distance from one antenna to the
location of the obstacle in miles
d2 = distance from the obstacle to the other
antenna in miles
D = total distance between the antennas in
miles ( D = d1 + d2 )
F = frequency in GHz
Dr. Tahseen Al-Doori
Example
 Figure shows a point-to-point communications link
that is 10 miles long. There is an obstacle that is 3
miles away and 40 feet tall. So the values and the
formula to calculate the radius of the Fresnel zone
at a point 3 miles from the antenna are as follows:
 N = 1 (for first Fresnel zone)
 d1 = 3 miles
 d2 = 7 miles
 D = 10 miles
 F = 2.4 GHz
Dr. Tahseen Al-Doori
 So if the obstacle is 40 feet tall and the Fresnel
zone at that point is 67.53 feet tall, then the
antennas will need to be mounted at least 108 feet
(40' + 67.53' = 107.53') above the ground to have
complete clearance. If we are willing to allow the
obstruction to encroach up to 40 percent into the
Fresnel zone, we need to keep 60 percent of the
Fresnel zone clear. So 60 percent of 67.53 feet is
40.52 feet. The absolute minimum height of the
antennas will need to be 81 feet (40' + 40.52' =
80.52'). Later, you will learn that due to the
curvature of the earth, you will actually need to
raise the antennas even higher to compensate for
the earth’s bulge.
Dr. Tahseen Al-Doori
 When highly-directional antennas are used, the
beamwidth of the signal is smaller, causing a more
focused signal to be transmitted.
 Many people think that a smaller beamwidth would
decrease the size of the Fresnel zone.
 This is not the case. The size of the Fresnel zone
is a function of the frequency being used and the
distance of the link.
 Since the only variables in the formula are
frequency and distance, the size of the Fresnel
zone will be the same regardless of the antenna
type or beamwidth.
Dr. Tahseen Al-Doori
 The first Fresnel zone is technically the area
around the point source, where the waves
are in phase with the point source signal.
 The second Fresnel zone is then the area
beyond the first Fresnel zone, where the
waves are out of phase with the point
source signal.
 All of the odd-numbered Fresnel zones are
in phase with the point source signal, and all
of the even-numbered Fresnel zones are out
of phase.
Dr. Tahseen Al-Doori
Earth Bulge
 When you are installing long distance point-topoint RF communications, another variable that
must be considered is the curvature of the earth,
also known as the earth bulge.
 Since the landscape varies throughout the world, it
is impossible to specify an exact distance for when
the curvature of the earth will affect a
communications link.
 The recommendation is that if the antennas are
more than seven miles away from each other, you
should take into consideration the earth bulge,
since after seven miles, the earth itself begins to
impede upon the Fresnel zone.
Dr. Tahseen Al-Doori
 The following formula can be used to
calculate the additional height that the
antennas will need to be raised to
compensate for the earth bulge:
H = D^2 ÷ 8
H = height of the earth bulge in feet
D = distance between the antennas in miles
Dr. Tahseen Al-Doori
 You now have all of the pieces to estimate how
high the antennas need to be installed.
Remember, this is an estimate that is being
calculated since it is assumed that the terrain
between the two antennas does not vary. You
need to know or calculate the following three
things:
 The 60 percent radius of the first Fresnel zone
 The height of the earth bulge
 The height of any obstacles that may encroach
into the Fresnel zone, and the distance of those
obstacles from the antenna
Dr. Tahseen Al-Doori
 Taking these three pieces and adding them
together gives you the following formula,
which can be used to calculate the antenna
height:
H = obstacle height + earth bulge + Fresnel
zone
 H=OB+ (D^2/8)+(72.2x((Nxd1xd2)/(FxD))^1/2
Dr. Tahseen Al-Doori
Example
 Fig. below shows a point-to-point link that
spans a distance of 12 miles. In the middle
of this link is an office building that is 30 feet
tall. A 2.4 GHz signal is being used to
communicate between the two towers. Can
you calculate the height of the antenna.
Dr. Tahseen Al-Doori
Antenna Polarization
 Another consideration when installing
antennas is antenna polarization.
 Although it is a lesser-known concern, it is
extremely important for successful
communications. Proper polarization
alignment is vital when installing any type of
antennas. Whether the antennas are
installed with horizontal or vertical
polarization is irrelevant, as long as both
antennas are aligned with the same
polarization.
Dr. Tahseen Al-Doori
 Polarization is not as important for indoor
communications because the polarization of the
RF signal often changes when it is reflected, which
is a common occurrence indoors.
 Most access points use low-gain omni-directional
antennas and they should be polarized vertically
when mounted from the ceiling. Laptop
manufacturers build diversity antennas into the
sides of the monitor. When the laptop monitor is in
the upright position, the internal antennas are
vertically polarized as well.
Dr. Tahseen Al-Doori
Antenna Diversity
 Wireless networks, especially indoor networks, are
prone to multipath signals.
 To help compensate for the effects of multipath,
antenna diversity, also called space diversity, is
commonly implemented in wireless networking
equipment such as access points (APs).
 Antenna diversity is when an access point has two
antennas and receivers functioning together to
minimize the negative effects of multipath.
Dr. Tahseen Al-Doori
 The Figure shows a picture of an access
point that uses antenna diversity.
Dr. Tahseen Al-Doori
 Since the wavelengths of 802.11 wireless
networks are less than 5 inches long, the
antennas can be placed very near each other and
be effective. When the access point senses an RF
signal, it compares the signal that it is receiving on
both antennas and uses whichever antenna has
the higher signal strength to receive the frame of
data. This sampling is performed on a frame-byframe basis, choosing whichever antenna has the
higher signal strength.
Dr. Tahseen Al-Doori
 The access point has to handle transmitting
data differently than receiving data.
 When the access point needs to transmit
data back to the client, it has no way of
determining which antenna the client would
receive from the best. The way the access
point can handle transmitting data is to
transmit using the antenna that it used most
recently to receive data. This is often
referred to as transmission diversity. Not all
access points are equipped with this
capability.
Dr. Tahseen Al-Doori
 There are many different kinds of antenna
diversity.
 The most common implementation of
antenna diversity utilizes one radio card, two
connectors, and two antennas.
 The question often gets asked why client
cards seem to have only one antenna.
Dr. Tahseen Al-Doori
 In reality, PCMCIA client cards typically have two
diversity antennas encased inside the card.
 Laptops with internal cards have diversity
antennas mounted inside the laptop monitor.
Remember that due to the half-duplex nature of
the RF medium, when antenna diversity is used,
only one antenna is operational at any given time.
In other words, a radio card transmitting a frame
with one antenna cannot be receiving a frame with
the other antenna at the same time.
Dr. Tahseen Al-Doori
Multiple Input Multiple Output
(MIMO)
 Multiple input multiple output (MIMO, pronounced “MYmoh”) is another, more sophisticated form of antenna
diversity.
 Unlike conventional antenna systems, where multipath
propagation is an impairment, MIMO systems take
advantage of multipath. There is much research and
development currently happening with this technology and
thus much disagreement about MIMO. There currently are
no official or de facto standards for the technology.
 MIMO can safely be described as any RF communications
system that has multiple antennas at both ends of the
communications link being used concurrently..
Dr. Tahseen Al-Doori
 How the antennas are to be used has not
yet been standardized. There are multiple
vendors providing different current and
proposed solutions. Complex signal
processing techniques known as Space
Time Coding (STC) are often associated
with MIMO. These techniques send data
using multiple simultaneous RF signals and
the receiver then reconstructs the data from
those signals. The proposed 802.11n
standard will include MIMO technology
Dr. Tahseen Al-Doori
Conclusion
 Don't ignore the importance of the antenna.
Choosing the right antenna and matching its
characteristics to the best propagation path
are the two most important factors in setting
up a communications circuit.
 The weakest link in the communications
circuit is the wrong propagation path.
 The best transmitter, antenna, and receiver
are of little use if the propagation path is
improper.
Dr. Tahseen Al-Doori
 The role of a wireless antenna is to direct
radio frequency (RF) power from a radio into
the coverage area.
 Different antennas produce different
coverage patterns, however, and need to be
selected and placed according to site
coverage requirements.
Dr. Tahseen Al-Doori
 Finally, remember that the choices made
during the antenna selection process can
make or break a WLAN system, just like the
choice of speakers can make or break a
stereo system.
 For example, a good antenna properly
deployed can reduce stray RF radiation, by
making the signal up to 100 times lower
outside of the work area, and thus much
harder to surreptitiously intercept.
Dr. Tahseen Al-Doori
Supplements
 Types of WiFi Antenna Designs
 Radio Frequency and Antenna Behaviors
and Characteristics
Dr. Tahseen Al-Doori