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Transcript of Present Horn
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Outline
Introduction
Equivalent and Radiation equation
Rectangular apertureHorn antenna
Pyramidal antenna
Dielectric covered antenna
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Introduction An aperture antenna contains some sort of
opening through which Electro magnetic
waves are transmitted or received
Aperture antennas are most common at
microwave frequencies
aperture Antennas include slots, waveguides,
horns, reflectors and lenses
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introduction
Aperture antennas are very practical due to itshigh directivity , able to flush mounted onthe surface of the spacecraft or aircraft and
covered with a dielectric material Which helps not disturb the aerodynamic
profile of the craft
since it is difficult to know the distribution ofcurrent in aperture antennas, radiation fieldsanalyzed by Field Equivalence Principle
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Equivalent and Radiation equation
The field equivalence is a principle by which
actual sources, such as an antenna and
transmitter, are replaced by equivalent sources
to find the radiated fields
a field in a lossy is uniquely specified by the
sources within the region plus the tangential
components of the electric field and magneticfield over the boundary, or the former over part
of the boundary and the latter over the rest of
the boundary 5
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Equivalent and Radiation equation
steps that must be used to form an equivalent
and solve an aperture problem:
a. Select an imaginary surface that encloses
the aperture so that the tangential components
of the electric and/or the magnetic field are
known
b. Over the imaginary surface form
equivalent current density Js and Ms which
take one of the following form
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Equivalent and Radiation equation
Equivalent for E and H some value andzero value in side the surface
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Electric and magnetic conductor equivalent
respectively 8
Equivalent and Radiation equation
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Equivalent and Radiation equation
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c. For far field approximation the electric and
magnetic field equation can be calculated from
the field vectors which are expressed in terms
Js and Ms.
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Equivalent and Radiation equation
Finally the electric and magnetic field equation
becomes
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Directivity
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RECTANGULAR APERTURES
The rectangular aperture antenna is the most
commonly used in microwave antenna because
of its aperture is easy to perform integration
Here we have three coordinate positions used
for analysis this are y-z, x-z and x-y
And their difference are:
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...RECTANGULAR APERTURES
the equivalent current densities (Jx, Jy, Jz, Mx,
My, Mz)
the paths from the source to the observation
point (rcos)
And differential area ds
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...RECTANGULAR APERTURES
We have three analysis for rectangular aperture:
Uniform Distribution on an Infinite Ground
Plane
Uniform Distribution in Space
TE10-Mode Distribution on an Infinite Ground
Plane
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Uniform Distribution on an Infinite
Ground Plane
Equivalent
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Radiation Fields: Element and Space
Factors
Since we now Ms and Js we can have vector field
F&A then
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For E plane pattern (=/2)
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H plane pattern (=0)
B idth
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Beam widths
It is the width of the beam at a point where
half of its peak value occur
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Side Lobe Level
Directivity
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Uniform Distribution in Space
Uniform distribution in space is similar to the
above but the aperture is not placed on the
infinite ground plane
TE10-Mode Distribution on an Infinite Ground
Plane: rectangular waveguide mounted on an
infinite ground plane. At the opening, the field
is usually approximated by the dominantTE10-mode for practical purpose
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HORN ANTENNA
Horn antenna is consists of a flaring metalwaveguide shaped like a horn
It is used to transmit radio waves from a
waveguide out into space, or collect radiowaves into a waveguide for reception
Invented in late 1800s & given emphasis in
the late 1930s
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HORN ANTENNA
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HORN ANTENNA
Their advantages are
low SWR(standing wave ratio) broad band width and
simple construction and adjustment.[
The gain of horn antennas ranges up to 25dB, with 10 -
20 dB being typical Operate over wide range of frequencies
(up to 1GHZ to 20 GHZ) Because they dont have resonant element
Minimum beam width that can be as minimum as 5 -10
it is Most widely used microwave antenna
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HORN ANTENNA
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HORN ANTENNA
Used as feed element
Radio astronomySatellite tracking
Communication dishes
A common element of phased arrays
Its widespread applicability is due to
simplicity in construction
ease of excitation
Versatility
large gain
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HORN ANTENNA
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HORN ANTENNA
Types of horn antenna
Pyramidal: flared in both side, rectangular cross section
Sectoral: flare in only single side
E-plane sectoral horn
H-plane sectoral horn
Conical: flared in all directions, circular cross section
Corrugated: parallel slots or grooves, insidesurface of the horn
Ridged horn: ridges or fins attached to the inside ofthe horn
conical and pyramidal horns are most widely used,because they have straight sides and are easier to
fabricate. 27
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HORN ANTENNA
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HORN ANTENNA
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Pyramidal Horn Antenna One whose opening is flared in both directions
This antenna is characterized by high gain
moderate bandwidth
low VSWR
relativity simple construction
widely used in various applications in themicrowave range such as
Feeders of reflectors and lenses
Receiving and/or transmitting antenna.
Currently used in applications where wide bandwidth isrequired, such as the technology WiMAX
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..Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
For a pyramid horn to be physically realizable
Pe and Ph must be equal For optimum pyramidal horn, low beam width
and high gain at a given frequency thedimensions of the pyramid are given by
Radiation characteristics determined using theequivalent principle techniques
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P id l H A t
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..Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
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P id l H A t
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.Pyramidal Horn Antenna
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Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
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00
030
060
090
0120
0150
0180
0150
0120
090
060
030
102030
10
20
30Relativepo
wer(dB
down)
P id l H A t
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..Pyramidal Horn Antenna
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P id l H A t
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..Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
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Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
Design Procedures
Specifications given for designGain
Operating frequency
Dimensions a and b of the rectangular feed waveguide
Objective of design determining other dimensions
a1, b1, e,h, Pe and Ph that lead optimum gain
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Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
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Pyramidal Horn Antenna
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..Pyramidal Horn Antenna
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Design Procedures
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Design Procedures
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Design
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Di l t i C d A t
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Dielectric Covered Apertures
Apertures covered their opening with dielectric
For the sake of protecting from environmental effects
The far-zone fields radiated from the antenna
covered with
A single lossless dielectric sheet cover of
thickness h, dielectric constant Er, unity
relative permeability and free-space phase
constant k0, are given by
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Dielectric Covered Apertures
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Dielectric Covered Apertures
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Di l t i C d A t
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Dielectric Covered Apertures
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In general
Aperture antennas are practical because of high
gain, can be flash mounted and covered withdielectric
their radiation characteristics are determined usingequivalent technique
Horns are invented with need in microwave,applicable in UHF and microwave frequencies
Have larger bandwidth, low SWR, high gain and
simple in construction Applicable as feeder, as standard calibration
antennas, elements of phased arrays and directiveantennas for radar guns and microwave meters
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