2.1.6 BEAM PATTERN SYNTHESIS OF ANTENNA.ppt

Presentation on Beam Pattern Synthesis.

1. 1
BEAM PATTERN SYNTHESIS
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INTRODUCTION
•WHAT IS IT?
–Deals With The Design Considerations Of Ant Sys
For Desired Radiation Characteristics.
•What are the Desired Radiation
Characteristics?
–Far field pattern having nulls in certain directions.
–Desired distribution.
–Narrow beam width.
–Low side lobes.
–Decaying minor lobes et al.
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Beam pattern synthesis-The
task
•To satisfy these desired chars by
means of
–Geo dim.
–Ant config.
–Excitation distri.
This method of design is called
synthesis.
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The Execution-
Classification Categories
•Category one
–Ant pattern possess null in desired
directions……..(Schelkunhoff).
•Category two
–Desired distri in entire visible range, also
called beam shaping……..
(FourierTransform/Woodward method).
•Category three
–Tech to produce patterns with narrow
beams and side lobes…….
(binomial/Dolph-Tschebyscheff methods)
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CREATION OF NULLS
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Far field geo of N element array of isotropic sources
AF for an N element equally spaced
non uniform amplitude and
progressive phase excitation is given
by
Letting
We can rewrite the 1
st
eqn as
Which has its roots as
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Final Eqn………
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Analysis of the eqn……
•If we rewrite the eqn as
• The magnitude of z always lies on the unit circle
for any value of…… d,  or .
• So if we plot for different d and ……..what do we
have?
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 & its Imp?
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So what happens if I vary
the phase…………?
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……So can anybody spot the difference…..
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FINAL TAKEAWAY
•The roots specified each correspond to a
null point. Only difference VR/IR.
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DESIRED DISTRI IN VR
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How do we achieve it…..?
•We have seen……………
•AF is periodic with 
•To satisfy this d
•If d<non unique sol
•If d>undesired grating lobes.

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NARROW BEAM WIDTH
& SIDE LOBES
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METHODOLOGIES
•3 WAYS
– Uniform array
– Binomial
– Dolhph-Tschebyschelf
•Narrow beamwidth
–U1----D2--B3
•Lower sidelobes
–B1--D2---U3
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Implementation Binomial
Series
•Same eqn stands
•Consider the amplitude
–a
n
represents a binomial expansion
represented by
•Taking positive coefficients for series exp
we have…………….
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•Represents a Pascal s triangle
•m=no of array elements
•Coefficients of exp=amplitudes of
elements
Implementation Binomial
Series
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•If even=2M and odd=2M+1 then for
–2 elements a1=1 (2M=2)
–3 elements 2M+1=3 ie 2a1=2---->a1=1/a2=1
–4 elements 2M=4 a1=3/a2=1
–5 elements 2M+1=5 2a1=6a1=3/a2=4/a3=1
Implementation Binomial
Series
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• No minor lobes for
/4 & 2
• However high
difference between the
amplitude of each
element compare 10
elements and see for
yourself.
• Hence low efficiency
• Low side lobes due
to this very reason.
Ten elements
binomial array
pattern
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Thank you!!!!!!!
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