Performance evaluation of circular microstrip

INTERNATIONAL JOURNAL OF ELECTRONICS AND
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 4, Issue 1, January- February (2013), pp. 236-249
IJECET
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PERFORMANCE EVALUATION OF CIRCULAR MICROSTRIP
PATCH ANTENNA ARRAY WITH DIFFERENT DIELECTRIC
SUBSTRATE MATERIALS

K. Karuna Kumari1, Dr.P.V.Sridevi2
1
Department of ECE, GITAM University, Visakhapatnam, A.P., India,
2
Department of ECE, Andhra University, Visakhapatnam, A.P., India,

ABSTRACT

In high-performance aircraft, spacecraft, satellite, and missile applications, where
size, weight, cost, performance, ease of installation, and aerodynamic profile are constraints,
and the low-profile antennas may be required. Presently there are many other government and
commercial applications, such as mobile radio and wireless communications that have similar
specifications. To meet these requirements, micro strip antennas can be used. There are
various types of micro strip patch antennas of which circular micro strip patch antenna is
considered.
This paper involves design, simulation of circular micro strip patch antenna in S-band
frequency used for Wi-Fi applications (2.0-2.5GHz) using a conventional coaxial probe feed
technique. Using design specifications like frequency range, dielectric permittivity of
substrate, substrate height, input impedance the electrical measurements like V.S.W.R,
Return Loss, will be carried out in MATLAB software and also observe the Radiation
Patterns with the different values of dielectric constants. The array of circular patch antenna
is also designed considering the cases of uniform and non-uniform arrays. The uniform array
is implemented with a linear array and non-uniform array is designed with Dolph-
Tschebycheff array. The radiation patterns of both the arrays are generated. All simulating
results are obtained by using MAT Lab soft ware.

KEY WORDS:Circular Micro strip Patch Antenna, Antenna Arrays, Dielectric Constant of
the Substrate, MATLAB soft ware.

236


1. INTRODUCTION
1.1 Theory of Microstrip Antenna:
Patch antennas play a very significant role in today’s world of wireless
communication systems. A Microstrip patch antenna is very simple in the construction using
a conventional Microstrip fabrication technique. The most commonly used Microstrip patch
antennas are rectangular and circular patch antennas. These patch antennas are used as simple
and for the widest and most demanding applications. Dual characteristics, circular
polarizations, dual frequency operation, frequency agility, broad band width, feed line
flexibility, beam scanning can be easily obtained from these patch antennas

1.2 Patch Antenna Materials:
In the wide range of antenna models there are different structures of Micro strip
antennas, but on the whole we have four basic parts. They are:
1) The patch 2) Dielectric Substrate 3) Ground Plane 4) Feed Line

Fig 1: Micro strip circular Patch Antenna

Physical Radius of the Circular Patch equationgiven by
F
a = 1/ 2
 2h  ∏F  
1 +  ln  2 h  + 1 . 7726 
 
 ∏εrF     (1)

8 . 791 X 10 9 (2)
F =
fr ε r

The effective radius of the antenna is obtained with equation given by
1/ 2
 2h  ∏ a 
a e = a 1 +  ln + 1 .7726  
 ∏ aε r  2 h  (3)

237


A thin metallic region which has different shapes and sizes of the patch where the ground
plane is usually of the same materialthe dielectric material is commonly known as substrate.
The dielectric constant for the materials range from 2.1 to ≈ 12

2.DESIGN OF CIRCULAR MICROSTRIP PATCH ANTENNA

2.1Cavity model
The circular patch antennas can only be analyzed conveniently using the cavity model
and this can be accomplished using a cylindrical coordinate. The major modes supported by a
circular patch antenna are the TMzwhere z is taken perpendicular to the patch and can be
found by treating the patch, ground plane and the substrate, whose height is smallas a circular
cavity.

2.2Equivalent Current Densities and Fields Radiated
Applying the Equivalence principle to the circumferential wall of the cavity, the
equivalent magnetic current density can be obtained and assuming a TM11z mode the field
distribution under the patch. The evaluation of equation of the electrical equivalent edge of
the disk and magnetic current density can be expressed as

) (3)
M a = −2nΧ E a ρ '= ae

Since the thickness of the substrate is very small, the filamentary magnetic current becomes

I m = hM = a 0 2 hE 0 J 1 (ka e ) cos φ '
ˆ
a (4)
'
I m = a e 2 V 0 cos φ
Where

V0 = hE 0 J 1 ( Ka e ) At φ = 0
The patch antenna can be treated as a circular loop and using the radiation equations the
expression is given by E r = 0 ;

( )
E ρ = − jk 0 a eV0 e − jk σr / 2 r [cos φJ 02 ]
(5)

Eφ =
( jk 0 a eV 0 e − jk σ r)[cos θ sin φ J 02 ] (6)
2r

Then the field in the principal plane reduced to when E-plane φ = 0 0 ,180 0 , 0 ≤ θ ≤ 180 0

Eρ =
( jk a V e
0 e 0
− jkσr
)[ J (7)
02 ]
2r
Eφ = 0

238


0 0 0
Also, H-plane ( φ = 90 ,270 ,0 ≤ θ ≤ 90 ) are:

Eφ =
( jk a V e )[cosφJ
0 e 0
− jkσr
]
02
2r (8)

Where J 02 = J 0 (k0ae sinθ ) − J 2 (k0ae sinθ )
'
(9)

J 02 = J 0 (k0 ae sin θ ) + J 2 (k0 ae sin θ ) (10)

3. MICROSTRIP PATCH ANTENNA ARRAYS

Microstrip antennas are used not only as single element but are very popular in arrays.
Arrays are very versatile and are used to synthesize a required pattern that cannot be achieved
with a single element. Arrays increase the directivity, and perform various other functions
which would be difficult with any one single element. In this paper presenting the two
different arrays

3.1. Uniform N-Element Linear Array
(Uniform spacing, uniform amplitude, linear phase progression)
A uniform arrayis defined as the uniformly-spaced identical elements of equal
magnitude with a linearly progressive phase from element to element.

φ1 = 0 φ2 = α φ3 = 2α … φ N = ( N − 1)α

Figure: 2Micro strip antenna arrays

3.2 Design equations of Uniform Linear Circular Array :
In this analysis insertingthe linear phase progression into the formula for the general
Nelement of array gives
ψ ψ ψ  Nψ 
jNψ
jN jN − jN ψ sin 
e −1 e e − e 2 2 2 j( N−1)
 2 
AF= jψ = jψ jψ ψ =e
2
Where ψ = α + kd cos θ (11)
e −1 −j ψ 
e e −e
2 2 2 sin 

2

239


The function Ψ is defined as the array phase functionand is a function of the element spacing,
phase shift, frequency and elevation angle.
If the position of the array is shifted so that the center of the array is located at the
origin, this phase term goes away. Then the array factor becomes
 N ψ 
sin  
AF =  2 
ψ  (12)
sin  
 2 

For the microstrip array antenna, the x-y plane (θ=pi/2, 0 ≤φ≤ pi/2, 3pi/2 ≤φ≤ 2pi) is the
principal E-plane. For this plane, the expression for the radiated fields is

E a (φ ) = E (φ ) × AF
k h   Nψ 
sin  0 cos φ  sin  
 2  sin  k 0 L cos φ  ×  2 
=  
k0h
cos φ  2  ψ 
sin  
2  2  (13)
3.3 Non Uniform N (odd)-Element Linear Array(Dolph-Tschebyscheff Array)
(Uniform spacing, but non uniform amplitude distribution)
Dolph-Tschebyscheff Array is primarily a compromise between uniform and binomial arrays.
Its excitation coefficients are related to Tschebyscheff polynomials. A Dolph-
Tschebyscheff array with no side lobes (or side lobes of −∞ dB) reduces to the binomial
design.
1.3 Design equations of Non Uniform (Dolph-Tschebyschef) Array:

P = 2 M + 1(odd ) (14)

' '

(E) = E +.....+ E + E + E + E +....+ E = 2I E {a + a cos( cosθ ) + a cos( kdcosθ) +...a
kd 2 cos( cosθ)}
Mkd
P M +1 2 1 1 2 M +1 0 0 1 2 3 M +1

(15)
M +1 M +1
∏ d
( AF ) P = ∑
n =1
a n cos[ 2 ( n − 1 )
λ
cos = ∑
n −1
a n cos[ 2 ( n − 1 ) u ] (16)

∏d (17)
u= cos θ
λ

P = 2 M (even ) (18)

( E ) P = E M + ... + E 2 + E1 + E1' + E 2 + ... + E M =
'

1 3 2M − 1
= 2 I 0 E 0 {a1 cos( kd cos θ ) + a 2 cos( kd cos θ ) + ...a M cos( kd cos θ )}
2 2 2 (19)

240


M M
∏d
( AF ) P = ∑a n cos[ 2 n − 1)
λ
cos θ ] = ∑a n cos[( 2 n − 1) u ]
n =1 n −1 (20)

4.SIMULATED RESULTS&DISCUSIONS
All simulated results are possible with the help of MAT Lab software. Output
parameters of physical radius &Effective radius of the circular patch and Directivity of micro
strip antennas with different values of dielectric constants are tabulated in table 1. From the
output parameters, observed that with the high value of dielectric constant 9.8(Alumina),The
antenna physical parameters like Physical Radius(a), Effective Radius(ae) of the antenna
1.1236cm, 1.1022cm. As well as The Directivity of the antenna is 5.33dB also reducedBut
with the low value of dielectric constant 2.23 (Duriod), the size of the antenna, a= 2.3585cm,
ae=2.25cm and Directivity of the antenna 7.3496dB are also increased.

Dielectric
Dielectric Dielectric
Constant of Dielectric Dielectric Dielectric
Constant Constant of
the Constant Constant Constant of
of the the
substrate of the of the the substrate
Parameters substrate substrate
4.7 substrate substrate 2.1
9.8 2.55
(FR4 ) 2.6 2.23 (Teflon)
( Alumina) (Rexolite14
(Noryl) (Duroid) (PTFE)
22)

Physical
Radius of the 1.1236 2.4307
1.6231 2.1837 2.2051 2.3585
patch ( cm)

Effective
radius of the 1.1022 1.5749 2.0918 2.1112 2.2500 2.3149
patch ( cm)

Directivity
7.3496
(dB) 5.3306 5.9865 6.9879 7.0310 7.5044

E-PLANE
HPBW 180.0000 180.0000 104.0000 102.0000 90.0000
94.0000
(in degrees)

H-PLANE
HPBW 86.0000 80.0000
84.0000 80.0000 78.0000 78.0000
(in degrees)

Table: 1 Physical Parameters Circular Microstrip Patch Antenna

The design of this circular micro strip patch antenna exhibits different values of VSWR and
Return Losses with different values of dielectric constants at the operating frequency of
2.5GHz. Shown inFig.3&Fig.4

241


Frequency Verses Return Losses for different values of Dielectric constant of
0

-2

-4

-6
Return Loss(dB)
-8

-10

-12 Er=9.8, Return Loss=-11dB
Er=4.7, Return Loss=-13dB
Er=2.23, Return Loss=-16dB

-18
1 1.5 2 2.5 3 3.5 4 4.5 5
Frequency (Hz) 9
x 10

Fig: 3 Return losses of circularmicrostrip with differentvalues of dielectric Constants At the
operating frequency of 2.5 GHz

Frequency Verse VSWR for Different Values of Dielectric Constant of
5.5
Er=2.1
5 Er=2.23
Er=2.55
4.5 Er=4.7
Er=9.8
4

VSWR
3.5

3

2.5

2

1.5

1
1 1.5 2 2.5 3 3.5 4 4.5 5
Frequency (Hz) 9
x 10

Fig: 4 VSWR at the different Values of dielectric
Constants at center frequency of 2.5 GHz

242


S-Band Frequency Verses Return Loss
0

-2

-4

-6 F6=2GHz
ReturnLoss(dB)
-8
F5=2.1GHz
-10
F4=2.2GHz
-12
F3=2.3GHz
-14

-16 F2=2.4GHz

-18 F1=2.5GHz

-20
1 1.5 2 2.5 3 3.5 4 4.5 5
Frequency (GHz) 9
x 10

Fig: 5 Return losses of Circular Microstripantenna at the different frequencies (2- 2.5GHz)
with low value of dielectric constant 2

S-Band Frequency verses VSWR(dB)&Return Loss(dB)
5

0
VSWR (dB)&Return Loss(dB)

VSWR(dB)
-5 Return Loss(dB)

-10

-15

-20
2 2.05 2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5
S-Band Frequency (GHz)

Fig: 6Return losses of Circular Microstrip antenna at the different frequencies (2- 2.5GHz)
with low value of dielectric constant 2

The design of the antenna exhibits good VSWR (2-1.1dB), Return Loss equal to -19dB to -
8dB) at2- 2.5 GHz(S-Band) frequency shown in Fig.5& Fig.6

243


S-Band Frequency
S.No VSWR(dB) Return Loss(dB)
(GHz)
-8
1 2 2
-9
2 2.1 1.8
-11
3 2.2 1.6
-13
4 2.3 1.5
-16.5
5 2.4 1.1
-19
6 2.5 1.05

Table: 2 return loss & VSWR of S-Band (2GHz- 2.5GHz) frequency.

The design of Circular Microstrip patch antenna is extended to implement with the antenna
arrays and their performance is evaluated for both Uniform and Non-Uniform circular arrays.
The Uniform Array is implemented with Linear Array and Non-uniform arrays is
implemented using Dolph-Tschebyscheff Arrays ,The radiation pattern of the array circular
array are plotted with different values of dielectric constants εr =2.23&9.8.

Non Uniform Linear Array with er=2.23) Uniform Linear Array with
0 0

-5 -5

-10 -10

Relative Amplitude in
-15 Relative Amplitude in
-15

-20 -20

-25 -25

-30 -30

-35 -35

-40 -40

-45 -45

-50 -50
-50 0 50 -50 0 50
θ In Degrees θ In Degrees

Fig: 7 Radiation patterns for non uniform and uniform linear array with εr =2.32&10 Element
circular array

244


Non uniform Linear Array with er=9.8 Uniform Linear Array with
0 0

-5 -5

-10 -10
Relative Amplitude (dB) Relative Amplitude (dB)
-15 -15

-20 -20

-25 -25

-30 -30

-35 -35

-40 -40

-45 -45

-50 -50
-50 0 50 -50 0 50
θ (Degrees) θ(Degrees)

Fig: 8 Radiation pattern for non uniform and uniform linear array with εr =9.8 &10 Element
circular array

Uniform Linear array with er=2.23 vs er=9.8
0
er=2.23
-5 er=9.8

-10

-15
Relative Amplitude(dB)

-20

-25

-30

-35

-40

-45

-50
-80 -60 -40 -20 0 20 40 60 80
θ (Degrees)

Fig.9 Radiation pattern for uniform linear array with εr = (2.23&9.8) &10 Element circular
array

245


Non-Uniform array with er=2.23 vser=9.8
0
er=2.23
-5 er=9.8

-10
Relative

-15

-20

-25

-30

-35

-40

-45

-50
-80 -60 -40 -20 0 20 40 60 80
θ (Degrees)

Fig: 10 Radiation pattern for Non uniform (Dolph-Tschebyscheff) linear array with εr =
(2.23&9.8) &10 Element circular array

Rectagular Plot of Non-Uniform vs Uniform array with er=2.23
0
Non Uniform array
-5 Uniform array

-10

-15
Relative Amplitude in dB

-20

-25

-30

-35

-40

-45

-50
-80 -60 -40 -20 0 20 40 60 80
θ in Degrees

Fig: 11 Comparison Radiation patterns of Uniform& Non uniform (Dolph-Tschebyscheff)
linear array with εr = 2.23&10 Element circular array

246


Rectagular Plot of Non-Uniform vs Uniform array with er=9.8
0
Non Uniform Array
-5 Uniform

-10
Relative Amplitude (dB)
-15

-20

-25

-30

-35

-40

-45

-50
-80 -60 -40 -20 0 20 40 60 80
θ (Degrees)

linear array with εr = 2.23&10 Element circular array

Relative Non Uniform array with er=2.23 vs 9.8
0
er=2.23
-10
er=9.8
-20

-30
-40

-50
-80 -60 -40 -20 0 20 40 60 80
θ (Degrees)
Relative Uniform array with er=2.23 vs 9.8
0
er=2.23
-10
er=9.8
-20

-30
-40

-50
-80 -60 -40 -20 0 20 40 60 80
θ (Degrees)

Fig.13Comparison Radiation patterns of Uniform&Non uniform (Dolph-Tschebyscheff)
linear array with different
εr = 2.23&9.8,10 Element circular array

247


er=2.23
0

Non Uniform array
-10
Uniform array
-20

-30

-40

-50
-80 -60 -40 -20 0 20 40 60 80
θ(Degrees)
er=9.8
0

Non Uniform array
-10
Uniform array
-20

-30

-40

-50
-80 -60 -40 -20 0 20 40 60 80
θ(Degrees)

linear array with different εr =2.23&9.8, 10 Element circulararray

Dielectric SLL of Non
SLL of Uniform linear
S.No constant of Uniform linear
circular array
Substrate (εr) circular array
1 1 -30 -13.5
2 2.23 -29 -13.5
3 4.4 -28 -13.5
4 9.8 -27 -13.5

Table: 3comparisons between uniform &non uniform circular array
SLL with different εr values

Dielectric constant of substrate verses Side Lobe Level(dB)
-12

-14

-16
Uniform array
-18 Non Uniform array
id o e e l(d )
S e L b L ve B

-20

-22

-24

-26

-28

-30
1 2 3 4 5 6 7 8 9 10
Dielectric constant of substrate(er)

Fig: 15 Plot between dielectric constant of substrate verses Side Lobe Level (SLL) of for
uniform & Non uniform

248


5. CONCLUSIONS

In this paper, we presented the design of a circular patch antenna with operating frequency of
2.5 GHz. The design of antenna with lower value of substrate dielectric constant of exhibits good
VSWR approx.1.1dB, Return Loss approx equal to -17dB, Directivity equal to 7.5 dB The design is
extended to microstrip antenna array and the performance is evaluated for both Uniform and Non-
Uniform arrays. The Uniform Array is implemented with Linear Array and the Non-Uniform array is
implemented using Dolph-Tschebyscheff Array .The radiation pattern is plotted with different values
of dielectric constant εr =2.23 (RT Duroid 5880) &9.8(Alumina) From the simulated results observed
that in the case of uniform linear arrays, as array size is increased to increase the directivity but the
Side Lobe Levels are at -13.5dB, with εr=2.23&9.8. But in case of Non Uniform Linear Array (Dolph-
TschebyscheffArray) with εr=2.23&9.8, provides optimum beam width and Side Lobe Levels are
reduced to -30dB&-28 dB. From the simulated results we concluded that for the Design of Circular
Micro strip Antenna with Non Uniform Distribution of(Dolph-Tschebyscheff) Array with lower
values of dielectric constant, εris preferred to get the optimum Directivity, Reduced Side Lobe Level,
Good VSWR, Good Return Losses . Circular microstrip antenna array is good choice to usein Wi-Fi
Modems, Wi-Max applications.

6. REFERENCES

[1] Balanis C.A. (2005) Antenna Theory: Analysis and Design, John Wiley & Sons
[2] Ramesh G, Prakash B, Inder B, and Ittipiboon A. (2001) Microstrip antenna design
handbook, Artech House.
[3] G. Breed, “The fundamentals of patch antenna design and performance,” From
Highfrequency electronics Summit technical media, LLC, March 2009.
[4] J. R James and P. S Hall, Handbook of microstrip antennas, Stevenage, UK: Peregrines,
1989.
[5] K. A Michalski and D. Zheng, “Analysis of microstrip resonators of arbitrary shape,”
IEEE Trans. Microwave Theory Tech, vol. 40 pp. 112-199, Jan. 1992
[6] K. R. Carver and J. W. Mink, “Microstrip Antenna Technology,” IEEE Transactions on
Antennas and Propagation, vol. AP-29, pp. 2- 24, January 1981.
[7] Gonca, C. (2005) Design, Simulation and Tests of Low-cost Microstrip Patch Antenna
Arrays for the Wireless Communication Turk J Elect Engin, 13 (1)
[8] Burkholder, R and Lundin, T. (2006). Antenna and Radiation Pattern.IEEE
Transactions on Antennas and Propagation, 53(2)
[9] Richards, W.F. (1988) Microstrip Antennas. Theory, Application and Design Van
Reinhold Co., New York
[10] Kin-Lu Wong, Compact and Broadband Microstrip Antennas, Jon Wiley & Sons,
Inc., 2002
[11] J. R. James and P. S. Hall, Handbook of Microstrip Antennas, Peter Perigrinus
Ltd.,London, 1989
[12] K. O. Odeyemi, D. O. Akande, E. O. Ogunti, “Design of an S-Band Rectangular Microstrip
Patch Antenna” European Journal of Scientific Research Vol.55 No.1 (2011), pp.72-79
[13] B.Ramarao, M.Aswini, D.Yugandhar andDr.P.V.Sridevi, “Dominant Mode Resonant
Frequency Of Circular Microstrip Antennas With And Without Air Gap” International journal
of Electronics and Communication Engineering &Technology (IJECET), Volume 3, Issue1,
2012, pp. 111 - 122, Published by IAEME.
[14] Mahmoud Abdipour, GholamrezaMoradi and Reza SarrafShirazi, “A Design Procedure For
Active Rectangular Microstrip Patch Antenna” International journal of Electronics and
Communication Engineering &Technology (IJECET), Volume 3, Issue 1, 2012, pp. 123 -
129, Published by IAEME.

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Performance evaluation of circular microstrip

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