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Transcript of Array Antennas..!!!
Frenil Shah ( 10BEC129)
Project Guided By: Dr. Dhaval Pujara
Array Antenna – An Introduction
Linear Arrays with Uniform Amplitude Distribution
Linear Arrays with Non-Uniform AmplitudeDistribution
LINEAR ANTENNAS WITH
UNIFORM AMPLITUDE DISTRIBUTION
Ordinary End-Fire Array
Hansen Woodyard End-Fire Array
LINEAR ANTENNAS WITH
NON-UNIFORM AMPLITUDE DISTRIBUTION
Placed along the axis perpendicular to the direction of maximum radiation.
Maximum radiation is obtained in the direction of axis
perpendicular to the array axis.
All the elements are in same phase.
Beta (initial phase difference) will be zero.
Used for long distance communication where directivity needed to be strong.
Elements are fed with the current that is equal in magnitude but opposite in phase.
Maximum radiation occurs in the direction to the axis of linear elements.
Used in satellite dish antennas, where a very high directivity is needed.
Directivity of broadside array is more than that of endfire array.
Beamwidth of endfire array is greater than that of broadside array.
HANSEN-WOODYARD ENDFIRE ARRAY
Special case of the endfire array.
Introduced to provide more directivity as compared to the normal endfire array.
The Beamwidth of ordinary endfire array is greater than that of Hansen Woodyard array.
The directivity of the Hansen Woodyard array is higher than that of ordinary endfire array.
Number of Sidelobes is more in Hansen Woodyard array as compared to ordinary endfire array.
PHASED ARRAY (SCANNING ARRAY)
Direction of maximum radiation of linear antennas is definite.
Initial phase (phi) is continuously changed between the elements.
Maximum radiation happens in one definite direction only regardless of rotation of antenna.
Used by warships of many navies.
Phased array radars allow a warship to use one radar system for many purposes.
Elements in the array are arranged according to the coefficients of the binomial series.
Binomial arrays do not exhibit any minor lobes.
Exhibit larger Beamwidth compared to uniform and Dolph Tchebyscheff’s designs.
Wide variations between the amplitudes of the different elements of the array, especially for an array with large number of elements.
This leads to low efficiencies.
A compromise between uniform and binomial arrays.
Its excitation coefficients are related to Tschebyscheff polynomials.
A Dolph-Tschebyscheff array with no side lobes reduces to the binomial design.
DOLPH TCHEBYSCHEFF’S ARRAY
In binomial type distribution, Sidelobes are less but the Beamwidth is maximum as compared to uniform, edge and Dolf Tchebyscheff’s array.
In Dolf Tchebyscheff’s distribution, Sidelobes and Beamwidth are balancing each other.
It’s an optimum distribution having Sidelobes less than the uniform array and Beamwidth less than the binomial array.
All of the elements are in one single plane.
Provides large aperture and used for directional beam control by varying the relative phase of each and every element.
Used in Telecommunications and Radar Systems.
Provides a 2D angular scan, both horizontal and vertical scans.
Unlike 2D planar arrays, circular arrays are basically 1D linear arrays but in a circular form.
Unlike linear arrays, a circular array can scan horizontally for 360 with no distortions.
Unlike linear arrays, distortions in the array pattern of a circular array due to mutual coupling effect are same for each element and this makes it easier to deal with the mutual coupling effect.
Antenna elements arranged around a circular ring.
With specific variations,radiation pattern can be change.
PLANAR ARRAYS (CONT.)
High gain width lower side lobes.
Ability to permit the beam to jump from one target to the next in a few microseconds.
Ability to provide an agile beam under computer control.
Arbitrarily modes of surveillance and tracking.
Multifunction operation by emitting several beams simultaneously.
Fault of single components reduces the capability and beam sharpness, but the system remains operational.
Beam steering in two planes or even the digital beam forming is possible.
Source : http://www.wikipedia.org
Understood a master thesis on 'REFLECTOR FEED INTERACTION FOR PARABOLIC REFLECTOR ANTENNAS' by MARK A. APELDOORN and prepared a report on it.
Got acquainted with new matlab functions and learnt how to implement them.
Learnt how to make a dynamic presentation with the help of Cloud based presentation software 'PREZI' and implemented it in our own presentation.
Constantine A. Balanis, "AntennaTheory-Analysis and Design", 2nd Edition, John Wiley and Sons ,New York, N.Y.,1982
"The Antenna Theory Website" [ http://www.antenna-theory.com ]
Thomas A. Milligan,"Modern Antenna Design", 2nd Edition, John Wiley and Sons,New York, N.Y.,1982
Shashi Kumar. D,"Analysis of Radiation patterns of Broadside and Endfire arrays due to seperation of elements and number of elements" in National Conferences On Electrical Sciences (NCES)
DEVELOPMENT OF MATLAB CODES OF ARRAY ANTENNAS
ARRAY ANTENNA-AN INTRODUCTION
Performance of single-element antenna is limited.
Multiple antennas (elements) are arranged to achieve a given radiation pattern.
Causes radiation to be maximum at a particular direction and minimum at other directions
Overall radiation pattern = Array factor X radiation pattern of the element.