7/25/2019 BSA and EFA
1/12
BSA and EFA
D.ARUN KUMAR
DEPT OF ECE
7/25/2019 BSA and EFA
2/12
7/25/2019 BSA and EFA
3/12
7/25/2019 BSA and EFA
4/12
7/25/2019 BSA and EFA
5/12
7/25/2019 BSA and EFA
6/12
TAPERING OF THE ARRAYS
The techniques used for reduction of unwanted side lobes arecalled tapering.
As the amplitudes of currents in the linear array sources is non-
uniform, one way of reducing the side lobe level is to make the
center source radiate more energy than the end ones, i.e. Tapering
is done form the center to end as per some prescription.
In this prescription which derives the name of the array.
Eamples!
Binomial array - tapering follows coefficients of binomial series.
Dolph Tchebysceff arrays - tapering follows coefficients ofTchebysceff polynomial.
7/25/2019 BSA and EFA
7/12
Binomial array
In binomial array side lobes can be totally eliminated if
a" The spacing between the two consecutive elements
does #$T eceed half the wavelength and
b" The current amplitudes in the radiating sources areproportional to the coefficient of successive terms of
the binomial series.
7/25/2019 BSA and EFA
8/12
Binomial arrayDisa!"an#a$es
The width of the beam %&'()" increases, thus
decreasing the directivity.
*or designing a large si+e array %more number of
elements" larger amplitude rate of currents for theradiating sources is required, which is difficult to
achieve in practice.
7/25/2019 BSA and EFA
9/12
Dolph Tchebysceff arrays
These arrays produce the narrowest beam width for a
given side lobe level or vice-versa.
As for a specified side lobe level, the narrowest beam
width is achieved by this distribution, it is consideredto be optimum. %d less than r equal to lamba by "
(y this method it is possible to design a high gain
narrow beam antenna for side lobe levels of -db
in /&* and 0&* bands especially for radars.
7/25/2019 BSA and EFA
10/12
Dolph Tchebysceff arrays A!"an#a$es
It provides a minimum, rather than optimum beam
width for required side-lobe reduction.
It results in side lobes of same amplitude as against
progressively decreasing levels of uniformdistribution.
Tapering is not etreme, unlike in (inomial arrays.
i.e, the ratio of current between the centre element
and end elements is small providing easier feed
design.
7/25/2019 BSA and EFA
11/12
Pattern Multiplication
1et E be the total field of the array of non-isotropic sources,
Ei2%3, 4" the field pattern of individual source,
Ea2%3, 4" be that of the array of isotropic point sources,
Epi2%3, 4" be the phase pattern of individual source and
Epa2%3, 4" be the phase pattern of array of isotropic point sources,
then by definition
E2 5Epi2%3, 4" Ea%3, 4" 6 mulitiplied by5Epi2%3, 4" 7 Epa2%3, 4" 6 is true for
any number os similar sources
7/25/2019 BSA and EFA
12/12
Pattern Multiplication
The total phase pattern is the addition of the phase
patterns of the individual sources and that of the array
of isotropic point sources. This concept is known as
pattern multiplication.A!"an#a$es%
8ives a speedy method of sketching the pattern of
complicated arrays 9ust by inspection.
'roves to be a useful tool in designing antenna arrays.
This method is very accurate as point by point
multiplication of pattern is carried out.