This document discusses omni-directional antennas. It explains that omni-directional antennas radiate radio waves uniformly in all directions within a single plane. They have a doughnut-shaped radiation pattern with little power transmitted along the central axis. Omni-directional antennas are commonly used in mobile phones, Wi-Fi routers, walkie-talkies and other wireless devices because they provide 360-degree coverage without requiring precise alignment. However, their gain may decrease in the presence of interference or signal fading.

1. OMNI-DIRECTIONAL
ANTENNA
By,
PRAVEEN M K
I M.TECH(DCN)
9913107002
1/25/2014
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2. WHY…….????

Directionality:
◦ Omni (360º coverage) directional
◦ Directional (limited range of coverage)
Compatibility
Should not require any alignment during the
fixation.
Light weight
Easy implementation
Low power consumption
Low cost
Easily replaceable

Gain:
Gain should be more.
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3. ODA:

An Omni-Directional Antenna(ODA) is an
antenna which radiates radio wave power
uniformly in all directions in one plane, with
the radiated power decreasing with
elevation angle above or below the plane,
dropping to zero on the antenna's axis.
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4. ANTENNA
CHARACTERISTICS:
(i)Radiation Pattern:
 The radiation pattern is often
described as "doughnut shaped".
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5. Contd….,
In this case, along the z-axis, which would correspond to
the radiation directly overhead the antenna, there is very
little power transmitted. In the x-y plane (perpendicular to
the z-axis), the radiation is maximum.
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6. (ii)Gain:
Antenna gain is a measure for antennas efficiency.
 Gain is the ratio of the maximum radiation in a
given direction to that of a reference antenna for
equal input power.
 Generally the reference antenna is an isotropic
antenna.
 Gain is measured generally in “decibels above
isotropic (dBi)” or “decibels above a dipole (dBd).
dBi = dBd + 2.15

**(Gain is mainly depends on the mechanical size
of an antenna)**
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7. Types of ODA:
Whip antenna
 Rubber duck antenna
 Ground plane antenna
 Discone antenna etc…..,

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8. How it looks like…???
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9. Used in,
Mobile phones
 Wi-fi modem’s
 Walkie-Takie’s
 Cars-(FM antenna)
 Wireless Microphones(Mike) etc…,

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10. Limitations:

Although their gain should be very high, due
to some external factors i.e..,(interference,
fading etc..,) their gain should get decreased.
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