Side Lobe Level (SLL) Reduction Methods in Antenna

Reduction Methods for

Side Lobe Levels (SLL) in

Antenna

PREPARED BY – DARSHAN BHATT

(150320705001)M.E – E.C – SEM 2

Contents Introduction & Basic concept of SLL

Requirements of lower SLL

PART I – SLL reduction in antenna array using weighting

function

PART II – SLL reduction in Microstrip patch array

antenna

Conclusions

References

Antenna Enginnering Design (AED)

2

Introduction Radiation pattern of an antenna having various parts

called “lobes” which are classified as main lobe, back lobe, minor lobe and side lobes. [3]

Here we discussed about the side lobes in antenna radiation pattern and its various reduction methods.

In the antenna, side lobe level is the main problem which causes the wastage of energy at transmitter side. [3]

So first we discussed about basics of SLL and than its reduction mechanism for antenna array and microstrip patch antenna array. [3]


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Basics of SLL A side lobe is “a radiation lobe in any direction

other than the intended lobe”. [3] Usually it is adjacent to the main lobe. [3] The ratio of power density in the lobe to the main

lobe is called “side lobe ratio” or “side lobe level (SLL)”. [3]

Higher SLL is the serious problem at transmitter side because it is totally a wastage of power in other directions or undesirable direction. [3]

We discussed various methods of SLL reduction in later part of this presention.


4

(cont)

Fig 1 : Polar pattern of antenna radiation lobes [3]Fig 1 : Polar pattern of antenna radiation lobes [3]Antenna Enginnering Design (AED)

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(cont)

Fig 2 : Linear plot of Power pattern [3]Fig 2 : Linear plot of Power pattern [3]


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Requirements of low SLL It is obvious that desirable SLL value is as small as possible

that means minimum power is radiated in undesirable

direction and maximum power radiated in desired direction.

[3]

Requirement of lower Side lobe level ratio is in the field of

radar engineering. [3]

In most RADAR systems, low side lobe ratios are very

important to minimise false target indication through the side

lobes. [3]


7

Major Aspects The major aspects of this presentation is the

reduction phenomena of SLL particularly for the

two cases of antenna –

1. Side Lobe Level (SLL) reduction in antenna array

using weighting function [1]

2. Side Lobe Level (SLL) reduction in Microstrip

patch antenna array [2]


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PART - I Side Lobe Level Reduction in Antenna Array using

Weighting Function


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SLL in Antenna Arrays Array antennas are generally used for the applications

which require high gain and higher directivity. [3] Array antenns are nothing but array (group) of

antenna elements. [3] The most useful application is specialized multi

functional RADAR system. [1] SLL is the major problem in arrays of antenna

radiation pattern. [1][3] Here, to reduce SLL different windowing techniques

are used for linear, planner or circular arrays of antenna. [1]


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(cont.) Most of the applications recommend to attain high

main lobe to side lobe ratio.[1] SLL in array antenna can be reduced by varying

these parameters –

1. No of antenna elements

2. Element spacing

3. Window co-efficients [1] Result of antenna gain pattern is simulated by

applying different windows like Kaiser window, Hamming window, Hann and Blackman window.[1]


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Linear Arrays of Antenna A linear array is one consisting of a group of identical

elements placed in one dimension along a given direction.

[1]

It may have equidistance or non-equidistance.

Fig-3 shows linear array antenna consisting of N identical

elements.

Element spacing : ‘d’

Phase difference : kd sin(β)


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Linear Arrays of Antenna

Fig 3 : N element linear array antennas [1]Fig 3 : N element linear array antennas [1]


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Planner Arrays of Antenna A planner array has all its elements located in a

single plane occupying a definite area. [1] Below Fig-4 shows N×N planner configuration

made from rectangular grid.

Fig 4 : N element Fig 4 : N element planar array planar array antennas [1]antennas [1]


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Circular Arrays of Antenna A circular arrays provide 2D angular scan. It is nothing but 1D linear arrays but in circular

manner.

Fig 5 : N element Fig 5 : N element Circular array Circular array antennas [1]antennas [1]


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Simulation Results using MATLAB

To observe the results of different windows on linear,

planner and circular arrays MATLAB tool is used.

For linear array MATLAB program is used and for

rectangular and circular array MATLAB GUI is used.

First we will represent the radiation pattern of all

three cases of antenna using MATLAB.


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Fig:6 - Simulation Result for Linear array


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Fig:7 - Simulation Result for Rectangular array


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Fig:8 - Simulation Result for Circular array


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Discussion on simulation results

There exist side lobe levels in all three types of

array antenna cases.

Now we will discuss about reduction of side lobe

levels of different antenna arrays using Kaiser,

hamming, Hann and Blackman window.

In that first we will discuss about radiation pattern

of linear array antenna by applying different

windows.Antenna Enginnering Design (AED)

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Fig:9 - Simulation Result for Linear array using Kaiser

Window


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Fig:10 - Simulation Result for Linear array using Hamming

window


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Fig:11 - Simulation Result for Linear array using Hann

Window


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Fig:12 - Simulation Result for Linear array using Blackman

Window


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Table : Peak SLL Comparison for Linear Array case


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Simulation Result for Rectangular array antenna

Fig 13 : Simulation with Kaiser window

Fig 14 : Simulation with Blackman window


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Simulation Result for Circular array antenna

Fig 15 : Simulation with Kaiser window

Fig 16 : Simulation with Blackman window


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Conclusion from simulation results From the above table and figures for the case of

linear, rectangular and circular antenna array, it is clear that the reduction of side lobe can be possible by using any type of window.

In the case of linear antenna array the peak side lobe level in Kaiser window is higher than Hamming, Hann and Blackman window.

The peak side lobe level of Blackman window is -80 dB indicating maximum side lobe reduction for the case of linear arrays of antenna.


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PART - II Side Lobe Level Reduction in Microstrip Patch Antenna

Array


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Reduction method of SLL Microstrip antennas, due to features of light weight,

small size and planar structure are very attractive in RADAR applications. [2]

Important parameter in RADAR is SLL which should be lower than -25 dB for RADAR applications. [2]

We can reduce SLL for microstrip patch array using a special technique and make possible it for a use in RADAR and navigation fields.[2]

SLL Level can be reduced by placing air core below a single circular patch antenna and narrow strip fence in between the elements. [2]


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Structure

Fig 17 : Circular Patch antenna Fig 17 : Circular Patch antenna with air core fed through with air core fed through

coaxial probe [2]coaxial probe [2]

Fig 18 : Circular arrays with air core and strip fences fed by Fig 18 : Circular arrays with air core and strip fences fed by coaxial probe [2]coaxial probe [2]


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Fig:19 - Resultant Graph using HFSS & CST


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Fig 20: SLL reduction Fig 20: SLL reduction using air core below the using air core below the patch [2]patch [2]

Fig 21: SLL reduction Fig 21: SLL reduction using air core and strip using air core and strip fences [2]fences [2]


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Conclusion From the first part, we can conclude that from

different window techniques, by using Blackman windowing SLL can be maximally reduced at negligible level for linear and circular array antenna. [1]

From Part 2, we can conclude that to reduce SLL for microstrip patch array antenna, air core and narrow strip fences are used in between two elements. [2]

We can reduce SLL for microstrip patch arrays up to -45 db level which is a very good achievement in reduction of SLL for better use in RADAR engineering. [2]


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References [1]. R Sarker, M Islam, T Alam, Dr. M Haider, “Side

Lobe Level Reduction In Antenna Array Using Weighting Function”, IEEE conference on Electrical Engineering & Information & communication tech. (ICEEICT) 2014.

[2]. N Bayat, H.R.Hassani, S.M.Nezhad, “Side Lobe Level Reduction In Microstrip Patch Antenna

Array”, IEEE conference on Antennas & Propagation, Loughborough, UK, Nov 2011

[3]. “Antenna Theory – Analysis & Design” by C.A.Balanis


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Date post:	15-Apr-2017
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