Special Purpose Antenna
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Folded Dipole
Yagi-Uda
Log-Periodic
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Folded Dipole Antenna
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Dipole Antenna
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Folded Dipole Antenna
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Dipole
Antenna
Folded Dipole
Antenna
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Folded Dipole AntennaDesign
L = 143/f
where:L is in meters
f is in MHz
L = 468/fwhere:
L is in feet
f is in MHz
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Folded Dipole AntennaDesign folded dipole uses a 300 ohm balanced feeder line
elements can be any conductor from simple wires to copper or
aluminum tubing
tips of the antenna are folded back until they almost meet at the
feedpoint, such that the antenna comprises one entire wavelength
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Folded Dipole Antenna
Where:d1 is the conductor diameter for the feed arm of the dipoled2 is the conductor diameter for the non-fed arm of the dipoleS is the distance between the conductorsr is the step up ratio
Design
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Folded Dipole AntennaVoltage and Current
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Folded Dipole AntennaDescriptiona dipole antenna whose outer ends are folded back and
joined together at the center;
the impedance is about 300 ohms, as compared to 70 ohmsfor a single-wire dipole;
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Folded Dipole AntennaApplicationused in the simple FM dipole antennas that can be bought to
use as temporary FM broadcast antennas
used within other larger antennas such as the Yagi.
used to raise the impedance to a suitable value
well matched to 300-Ohm balanced transmission lines
widely used with television and frequency-modulation
receivers.
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Folded Dipole Antenna
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Yagi-Uda Antenna
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Yagi-Uda Antenna
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Yagi-Uda Antenna
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Yagi-Uda AntennaThe Elements of a Yagi
The Driven Element
where feed point is locatedand where the feed line isattached from the transmitterto the Yagi to perform thetransfer of power from thetransmitter to the antenna
resonant when the electricallength is 1/2 of the
wavelength, for the usedfrequency, applied to the feed
point
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Yagi-Uda AntennaThe Elements of a Yagi
Parasitic Elements
- element that is not directlyconnected to the feed line
- elements used for the purpose ofobtaining directional power gain
- reradiate power which they receivefrom the driven element
Directors
Reflectors
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Yagi-Uda AntennaThe Elements of a Yagi
Parasitic Elements
Directors slightly higher in frequency
than the driven element
length is 5% shorterprogressively than thedriven element
used to provide theantenna with directionalpattern and gain
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Yagi-Uda AntennaThe Elements of a Yagi Parasitic Elements
Reflector
protect the antenna againstthe parasitic signalscoming from the rear
resonant frequency is lowerand length is 5% longer
than the driven element the spacing will be between
.1 and .25 wavelength
Prevents antenna fromsending backward
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Yagi-Uda AntennaDesignThere are no simple formulas for designing
Yagi-Uda antennas due to the complexrelationships between physical parameters suchas element length, spacing, and diameter, andperformance characteristics such as gain and
input impedance.Wikipedia
http://en.wikipedia.org/wiki/Yagi-Uda_antenna
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Yagi-Uda AntennaDesign Guidelines
typical spacing between elements vary from about 1/10 to1/4 of a wavelength, depending on the specific design
elements are usually parallel in one plane, supported on asingle crossbar known as a boom.
the elements must be made of some kind of conducting material:
copper, aluminum, coaxial cable are best suited.
with coaxial cable, we can use only the shield or connect the shield
with the inner conductor. the horizontal stick (boom) can be made of anything.
if it is made of conducting material, the elements must be isolated
from the stick.
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Yagi-Uda AntennaDesign Guidelines
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Yagi-Uda AntennaDesign Guidelines
typical spacing between elements vary from about 1/10 to1/4 of a wavelength, depending on the specific design
elements are usually parallel in one plane, supported on asingle crossbar known as a boom.
the elements must be made of some kind of conducting material:
copper, aluminum, coaxial cable are best suited.
with coaxial cable, we can use only the shield or connect the shield
with the inner conductor. the horizontal stick (boom) can be made of anything.
if it is made of conducting material, the elements must be isolated
from the stick.
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Yagi-Uda AntennaDesign Guidelines
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Yagi-Uda AntennaDesign Guidelines
typical spacing between elements vary from about 1/10 to1/4 of a wavelength, depending on the specific design
elements are usually parallel in one plane, supported on asingle crossbar known as a boom.
the elements must be made of some kind of conducting material:
copper, aluminum, coaxial cable are best suited.
with coaxial cable, we can use only the shield or connect the shield
with the inner conductor. the horizontal stick (boom) can be made of anything.
if it is made of conducting material, the elements must be isolated
from the stick.
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Yagi-Uda AntennaDesign Guidelines
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Yagi-Uda AntennaDesign Guidelines
Driven Element
typically a
/2 dipole or
folded dipole
electrically
connected tothe feedline
Director/s
length is 5% shorter
progressively than the
driven element
the directors should
be roughly 1/4 awavelength apart
Reflector
length is5% longerthan thedrivenelement
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Yagi-Uda AntennaThe Elements
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Yagi-Uda AntennaDesignthese antennas are often empirical designs
using an element of trial and error, oftenstarting with an existing design modified
according to one's hunch. The result might bechecked by direct measurement or by computer
simulation.Wikipedia
http://en.wikipedia.org/wiki/Yagi-Uda_antenna
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Yagi-Uda AntennaDesign
http://www.changpuak.ch
/electronics
/yagi_uda_antenna.php
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Yagi-Uda Antenna**** YAGI UDA ANTENNA ****Design by www.changpuak.ch
---------------------------------------------------
Frequency : 100 MHz
Wavelength : 3000 mm
d/lambda : 0.003 ( min.: 0.001 , max.:
0.04 )D/lambda : 0.007 ( min.: 0.002 , max.:
0.04 )
Boomlength : 1200 mm
Elements : 3
Gain : 7.1 dB (approx.)
---------------------------------------------------
Reflector Length [mm] : 1463
Reflector Position [mm] : 0---------------------------------
Dipole Length [mm] : 1446
Dipole Position [mm] : 600
---------------------------------
Director Length [mm] : 1388
Director Position [mm] : 1200
---------------------------------
Calculations based on NBS TECHNICAL NOTE688
Len th mi ht be sli htl too lon .
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Yagi-Uda Antenna
http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf.html#Introduction
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Yagi-Uda AntennaDesign
YagiMAX: Yagi Uda antenna modelling software
YagiMAX Screenshots
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Yagi-Uda AntennaDesign Equal spaced, equal length directors may give higher gain at a
particular frequency, but the bandwidth is more narrow and largersidelobe levels are created.
Wide spacing will increase the bandwidth, but the sidelobes becomelarge.
By varying both the spacing and director lengths the pattern andthe pattern bandwidth may be more controlled.
More directors within a given boom length won't increase the gainby any great amount, but will give better control of the antenna'spattern over a wider range of frequencies in the band of design.
If the length of each succeeding director is reduced by a set factor(%), and increase the spacing of each succeeding director byanother factor, a very clean pattern with good pattern bandwidthcan be obtained. The trade off will be a small loss in the optimumforward gain (10% to 15%).
http://www.hamuniverse.com/yagibasics.html
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Yagi-Uda AntennaDescriptiona directional antenna designed to maximize
reception over long distances
familiar as the commonest kind of terrestrial TVantenna to be found on the rooftops of houses
used at frequencies between about 30MHz and3GHz, or a wavelength range of 10 meters to 10cm
the typical directivity is between 7dB and 9dB
named after two Japanese scientists whoinvented it
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Yagi-Uda AntennaApplication
used for amateur radio used during World War II for airborne radar sets
used for local television reception
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Log Periodic Antenna
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Log-Periodic Antenna
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Log-Periodic Antenna
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Log-Periodic AntennaDesign
Typically,
Typically,
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Log-Periodic AntennaDesign Bandwidth:
Number of Dipoles:
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Log-Periodic AntennaDesign the length and spacing of the elements of a log-
periodic antenna increase logarithmically fromone end to the other
diminish in size from the back towards the front element at the back of the array is a half
wavelength at the lowest frequency of operation
element spacing decrease towards the front ofthe array
the feed phase is reversed from one element tothe next to ensure that the phasing of thedifferent elements is correct
the direction of maximum radiation is towardsthe feed point
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Log-Periodic AntennaDescription the antenna input
impedance variesrepetitively when
plotted as a function offrequency andperiodically whenplotted against the logof the frequency
able to provide
directivity and gainwhile being able tooperate over a widebandwidth
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Log-Periodic AntennaDescription the radiation pattern of this RF antenna design stays broadly the
same over the whole of the operating band as do parameters likethe radiation resistance and the standing wave ratio
it offers less gain for its size than does the more conventional Yagi
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Log-Periodic AntennaApplication used where a wide range of frequencies is needed while still having
moderate gain and directionality
used on the HF portion of the spectrum where operation is required ona number of frequencies to enable communication to be maintained
used at VHF and UHF for a variety of applications, including some usesas a television antenna
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Turnstile Antenna
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Turnstile Antenna
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Turnstile AntennaDesign consists of two horizontal half-
wave antennas mounted atright angles to each other in
the same horizontal plane
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Turnstile AntennaDesignRadiation Pattern
The radiation pattern shown is the sum of radiation patterns from the
two dipoles, which produces a nearly omnidirectional pattern
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Turnstile AntennaDescription a set of two dipole antennas aligned at right angles to each other and
fed 90 degrees out-of-phase
When mounted horizontally the antenna is nearly omnidirectional onthe horizontal plane.
When mounted vertically the antenna is directional to a right angle toits plane and is circularly polarized.
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Turnstile AntennaApplication developed primarily for omnidirectional vhf communications
often used for communication satellites because, being circularlypolarized, the polarization of the signal doesn't rotate when thesatellite rotates
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Helical Antenna
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Helical Antenna
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Helical AntennaDesign The dimensions of the helix are determined
by the wavelength of the radio wavesused, which depends on the frequency.
In axial-mode operation, the spacingbetween the coils should be approximatelyone-quarter of the wavelength (/4), andthe diameter of the coils should beapproximately the wavelength divided by pi(/)
The length of the coil determines
how directional the antenna will be as wellas its gain; longer antennas will be moresensitive in the direction in which they point.
a ground plane at the driven end makes theradiation unidirectional from the far (open)end
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Helical AntennaDesign
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Helical AntennaDesign
Where:
is the radius of the helix is the pitch angle
S is the spacing between turns
L is the length of one turn
is the tangential unit vectordescribing the contour of the helix
Zo is the starting height of the helix
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Helical AntennaDesignpitch angle :
where:
s is the spacing from turn to turn
is the radius of the helix
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Helical AntennaDesign The helical countour can be described by
The x and y coordinates are given by
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Helical AntennaDesign the spacing b/w turns can be written as
z coordinate is given by
Combining the above relationships give
which describes any point on helix
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Helical AntennaDesign can be written in cylindrical coordinates by
using
and
giving
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Helical AntennaDesign the two equations are used in the development
of the electric field integral
equation for the helix
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Helical AntennaDesign The ground plane diameter is typically
0.94 in diameter at the centerfrequency
the radiating element is a helix ofwire, driven at one end and radiatingalong the axis of the helix
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Helical AntennaDescription An antenna that has the form of a helix
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Helical AntennaApplication typically used for applications where reduced size is a critical
operational factor
most suitable for Mobile and Portable High-frequency (HF) communications in the
1 MHz to 30 MHz operating range
used extensively for 27 MHz CB radio
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