Design of Low Interference High Directive Planar

Antenna with Schelkunoff Polynomial Method

P.Chaya Devi1*, K.Anusha* M.Kalpana*,L.Ganesh**
Department of E.C.E Department of E.C.E,
Raghu Institute of Technology*, Visakhapatnam ANITS**, Sangivalasa, Visakhapatnam
1
*pchayadevi@gmail.com India

Abstract--The words broadcasting, unicasting and multicasting radars, surveillance antennas demand patterns with special
are the well familiar terms in the field of communications and are characteristics (Beam widths). Due to the non complexity in
very important in describing various parameters in designing the implementation and ability to produce symmetrical-high
system. In the field of communications, the applications which directive beams, generally planar array antennas are used in
involve broadcasting needs an antenna of high directivity and
above mentioned applications. Planar antennas, with
should use the power effectively (low side lobes). Where in
applications that needs unicast-reception mainly needs high compromise in increased number of elements and size,
directivity (Zone of reception) and low interference (low side lobes) produces high directive beams [1] . To overcome this, a planar
antennas. There are some special applications like tracking radars, array design is proposed in this paper that provides high
surveillance antennas demand patterns with special characteristics directivity with reduced no of elements than a normal planar
(Beam widths). Due to the non complexity in implementation and array design.
ability to produce symmetrical-high directive beams, generally Other way of generating desired beam pattern is by
planar array antennas are used in above mentioned applications. synthesizing the antenna radiation pattern. Schelkunoff
Planar antennas, with compromise in increased number of polynomial synthesis method is one being used in linear array
elements and size, produces high directive beams. Other way of
design for suppressing radiation in undesired directions, there
generating desired beam pattern is by synthesizing the antenna
radiation pattern. Schelkunoff polynomial synthesis method is one by increases the directivity [2]. So in this paper Schelkunoff
being used in linear array design for suppressing radiation in method is extended to planar array antennas to produce high
undesired directions, there by increases the directivity. In order to directive beam with low cost and size. For implementing this
produce the desired beam with high directivity this paper proposes a paper MATLAB 7.10.0 software is used.
planar array design method and also extends the schelkunoff
polynomial method (confined as linear array synthesismethod ) to 2-D planar array:
planar array design to produce cost effective high directive
antennas. The radiation pattern characteristics (RPC) Directivity,
3dB beam width, Null-Null beam width and side lobe levels are
used to analyse the performance of proposed design and algorithm.
Keywords— Linear array; 3D planar array; Schel-kunoff
polynomial method; Directivity.

I. INTRODUCTION
Antenna is a metallic device that exists almost in all
electronic and communication equipments in the present
world, starting from a toy car to most advanced GPS system it
stands as the backbone. It is a transducer generally used for
radiating or receiving radio waves. With the advancement in
Fig.1 2-Dimensional planar array3
technology different antennas are emerged down the time. It
can be noticed that a single antenna element is not enough to The Planar array antenna with elements of M along X-axis and
meet the constraints for most of the practical applications and, elements of N placed along y-axis. The array factors is given
hence an array of antenna elements are being used to meet the as
requirements of the system. The three basic antenna array
structures are linear, planar and circular arrays. ( (
(1
The applications which involve broadcasting needs an
antenna of high directivity (in the zone of transmission) and
should use the power effectively (low side lobes). Where in ( (
(2
applications that needs uni-cast reception mainly needs high
directivity (Zone of reception) and low interference (low side where sin cosФ= cosγx, is the directional cosine from the x-
lobes) antennas. Some special applications like tracking axis (γx is the angle between X-axis and the r). In this paper

978-1-4799-7678-2/15/$31.00 ©2015 IEEE

for simulation it is assumed that a uniform spaced array with
sin ( sin ( sin (
an interval of dx and a progressive shift βx . Im1 denotes the 2 2 2 (5
excitation amplitude of the element at the point with sin ( sin (
2 sin ( 2
coordinates x= ((m-1) dx ,y = 0). In the fig 1 shown above, 2
this is the element of the m-th row and the 1stcolumn of the Where
array matrix.If N such arrays are placed at even intervals along
the y direction, a rectangular array is formed. We assume
again that they are equi-spaced at a distance dy ,and there is a
progressive phase shift βy along each row. We also assume
II. SCHELKUNOFF POLYNOMIAL METHOD
that the normalized current distribution along each of the x-
directed arrays is the same but the absolute values correspond The developed synthesis method by schelkunoff makes use
to a factor of I1n (n =1,...,N) . Then, the AF of the entire M x N of the polynomial form of the array factor in producing pencil
array is [3] beam radiation pattern for linear arrays. The linear array factor
in its polynomial form is written in complex form as [5]
( ( N −1
(3 F (u ) = ∑ a n Z n (6)
n =0
( (
The normalized array factor is obtained as Where an is excitation coefficient at each element and the
complex variable Z given as
( ( Z (u ) = exp( jkud x ) (7)
1 2 1 2
( , . (4 Equation (6) is a N-1 degree polynomial and the elements in
( ( the array are N with (N-1) zeros to be factored as
2 2
Where F (u ) = a N −1 ( z − z1 )( z − z 2 )......... .( z − z N −1 ) (8)
where the terms zn are the complex roots of the polynomial (as
yet unspecified). The magnitude of the array factor is thus
Proposed planar array design (3-D planar array): given as
F (u ) = a N −1 z − z1 z − z 2 ......... z − z N −1 (9)
The entire procedure for planar array synthesis with
schelkunoff is same except here due to M elements along x-
axis, (M-1) nulls can be placed in x direction and N elements
along y-axis allow to place (N-1) nulls to be placed in y
direction [6].
Nulls will be dedicated to the linear array factors given (1) and
(2) and their roots are calculated (10 & 11) as below
(M-1) roots given as
j ( kd sin θ cos φ ) (10)
Z =e x m m
xm
(N-1) roots given as
j (kd sin θ sin φ )
Z =e
y n n (11)
yn
Fig.2 Proposed planar array antenna4 and the planar array factor polynomial given as
As discussed previously the main drawback in designing a M N

high directive planar array antenna is, it need more array F ( z ) = a MN ∑ ( Z − Z xm ) m −1 ∑ ( Z − Z yn ) n−1 (12)
m =1 n =1
elements to be exited, in turn increases the cost and size of the The magnitude of the array factor is thus given as
system. On the other hand with the increase in size of array j ((m − 1) β + (n − 1) β )
more side lobes are developed and leads to interference and I =a e
x y (13)
mn mn
loss of power.This section focus in implementing a new planar
array design ‘3D- Planar array’ that overcomes the above III. RESULTS
mentioned drawbacks of 2D planar array design. Starting from
The Planar array antenna of 25 and 144 element length with
the planar array, where it is considered that the system has a
rectangular configuration of elements, the three dimensional uniform spacing of 0.65 λ and maximum radiation intensity in
array antenna shown in Fig. 2 is achieved by introducing a the direction of θ =00 and φ =00 is implemented in Matlab
number of planar arrays on the z axis. In this case, the array R2010a. The RPC of implemented array antennas are shown
factor is [4] in Table I. To reduce number of elements (and provides High
Directivity) the proposed 3D planar array antenna is
implemented and its RPC is detailed in Table I. The obtained
radiation pattern in planar array design is used in finding out
the best null locations, to direct the beam in desired direction
using Schelkunoff Polynomial method. The magnitude plot is
shown in Fig.1 and its RPC is given in Table 1.
Magnitude Vs Theta for Schelkunoff method & Planar array
0
Schelkunoff
-5 Planararray

-10

-15
agnitudeindB

-20
X: -24.82 X: 24.82
-25 Y: -27.99 Y: -27.99

-30
M

X: -41.87 X: 41.87
-35 Y: -29.95 Y: -29.95
Nulls
-40

-45

-50
-100 -80 -60 -40 -20 0 20 40 60 80 100
Theta in degrees

Fig. 3 Magnitude plot of schelkunoff synthesis planar array of length 25 elements

Table I Comparison of RPC for different planar array configurations

Antenna Planar Array Planar Array 3D Planar Array Schelkunoff
Parameters 5×5 12 × 12 5×5×5 5×5
0 0
Theta 08.5 23.5 24.50
3-dB Beam Width
Phi 470 170 470 490
Null-Null Theta 470 140 470 480
Beam width Phi 94 0
28 0
94 0
960
Directivity 39.45 dB 41.21 dB 43.93 dB 44.40 dB
Min -19.69 dB -09.30 dB -08.40 dB -14.46 dB
Side lobe level
Max -42.46 dB -41.22 dB -36.81 dB -39.75 dB
No of elements 25 144 125 25
Nulls - - - 420,190,-420,-190

REFERENCES
IV. CONCLUSION
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Symposium on Applied Computational Intelligence and Informatics,
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