Present Horn

7/31/2019 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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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

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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 for E and H some value andzero value in side the surface

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Electric and magnetic conductor equivalent

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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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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

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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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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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P id l H A t


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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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P id l H A t


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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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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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Di l t i C d A t


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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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Present Horn

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