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Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3470-3474 3470 
 

www.etasr.com Rao et al.: Study of Four Element Microstrip Antenna Array Using Patch Type Electromagnetic Band …  

 

Study of Four Element Microstrip Antenna Array 

Using Patch Type Electromagnetic Band Gap 

Structure 
 

K. Prahlada Rao 

Department Of PG Studies and Research 

in Applied Electronics 

Gulbarga University 

Gulbarga, India 

P. V. Hunagund 

Department Of PG Studies and Research 

in Applied Electronics 

Gulbarga University 

Gulbarga, India 

R. M. Vani 

University Science Instrumentation 

Centre 

Gulbarga University 

Gulbarga, India 
 

 

Abstract—This paper describes an enhancement in the 

performance of four element microstrip antenna array. The 

conventional microstrip antenna array is producing gain equal to 

6.81dB. With the introduction of U shape patch type 

electromagnetic band gap structure, the proposed microstrip 

antenna array is producing an improved gain of 20.33dB. It is 

producing reduced mutual coupling of -31.44, -36.41 and -

31.62dB respectively. The radiation characteristics of the 

proposed microstrip antenna array are improved with 

appreciable decrease in back lobe radiation and increase in 

forward power. It is resonating at single band at 5.53GHz, 

producing an overall bandwidth of 109.45%, against 4.89% of 

conventional microstrip antenna array. Microstrip antenna 

arrays are designed using Mentor Graphics IE3D software and 

measured results are obtained using vector network analyzer. 

Keywords-corporate feeding; gain; microstrip antenna array; 

mutual coupling; resonant frequency 

I. INTRODUCTION  

Antennas play an important role in proper working and 
development of various communication systems. Immense 
research towards the development of novel, sophisticated and 
efficient types of antennas is on the rise. Microstrip antennas 
are made of radiating patch or conductor and ground plane 
placed on either side of substrate. Microstrip antennas can be 
basically seen as sudden discontinuities which represent 
changes in their geometry and shape. These discontinuities are 
responsible for changes in the current, electric and magnetic 
field distributions. The most important inherent characteristics 
and serious limitations of microstrip antennas and arrays are 
narrow bandwidth and high mutual coupling values. The 
thickness of the radiating patch plays a crucial part when 
conductor losses are being calculated [1-7]. Applications 
involving microstrip antennas and arrays have driven research 
towards enhanced antenna bandwidth. Bandwidth of microstrip 
antennas and arrays can be enhanced by various methods like 
stacking, metamaterials, decreasing relative permittivity of the 
dielectric and defective ground structures. Nowadays, 
electromagnetic band gap (EBG) structures are being employed 
on a large scale to improve the efficiency of microstrip 

antennas. These structures consist of periodically placed unit 
cells. One of the notable features of EBG structures is that the 
dimensions of the unit cell are lesser than that of the radiating 
patch [8-16]. 

II. CONVENTIONAL MICROSTRIP ANTENNA ARRAY 

Conventional microstrip antenna array (CMAA) designed 
at 6GHz consists of four identical rectangular radiating patches. 
The substrate employed to design the antenna arrays is FR-4 
glass epoxy which has a dielectric constant of 4.2 and loss 
tangent of 0.0245. The height of the substrate is 1.6mm. Each 
of the radiating patches has dimensions of 15.73mm×11.76mm. 
The quarter wave transformer has dimensions of 
6.47mm×0.47mm. The feeding element has dimensions of 
6.52mm×3.05mm. CMAA is fed by corporate feeding 
technique. The distance between the adjacent radiating 
elements of CMAA is λ/4, where λ is the wavelength 
calculated at the design frequency of 6GHz. The schematic of 
CMAA is shown in Figure 1 and its dimensions are shown in 
Table I. 

 

 

Fig. 1.  Schematic of CMAA. 

The four radiating patches of CMAA are arranged in such a 
way that the distance between the adjacent radiating patches is 
the same with that of Figure 1. This setup is arranged to 
measure mutual coupling between the radiating elements. 
Moreover, the elements of CMAA are excited independently 
with the same amount of power. The S-parameters S21, S31 and 
S41 designate the mutual coupling coefficients. In the S-
parameters the first digit designates the output port and the 
second digit designates the input port. Figure 2 depicts the 
schematic of arrangement of elements of CMAA to measure 
the mutual coupling.  



Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3470-3474 3471 
 

www.etasr.com Rao et al.: Study of Four Element Microstrip Antenna Array Using Patch Type Electromagnetic Band …  

 

TABLE I.  CMAA PARAMETER VALUES 

Parameter Value(mm) 

Length of the patch (Lp) 15.73 

Width of the patch (Wp) 11.76 

Length of the quarter wave transformer (Lt) 6.47 

Width of the quarter wave transformer (Wt) 0.47 

Length of the 50Ω line (L1) 6.52 

Width of the 50Ω line (W1) 3.05 

Length of the coupler 3.05 

Width of the coupler 3.05 

Length of the 70Ω line (L2) 6.54 

Width of the 70Ω line (W2) 1.62 

Length of the 100Ω line (L3) 6.56 

Width of the 100Ω line (W3) 0.70 

Length of the feed line (Lf) 6.52 

Width of the feed line (Wf) 3.05 

 

 
Fig. 2.  Schematic of arrangement of elements of CMAA to measure 
mutual coupling. 

III. DESIGN OF PROPOSED MICROSTRIP ANTENNA ARRAY 

The unit cell of the EBG structure is depicted in Figure 3. 
The unit cell of the EBG structure employed consists of a U-
shape patch type. The dimensions of the unit cell are P=5mm 
and Q=4mm respectively. The EBG structure employed to 
enhance the performance of CMAA is depicted in Figure 4.  

 

Fig. 3.  Schematic of unit cell of EBG structure. 

 

Fig. 4.  Schematic of EBG structure.  

It consists of a matrix of 2 columns and 3 rows of U-shape 
patch type unit cells. The unit cells of the EBG structure are 
repeated after every 1mm along the x-axis and y-axis. The 
periodicity is represented by X. The proposed microstrip 
antenna array (PMAA) is designed by loading the EBG 
structure shown in Figure 4 on the surface and in between the 
radiating patches of CMAA. The schematic of PMAA is shown 
in Figure 5. In order to measure the change in the values of 
mutual coupling coefficients after the introduction of U-shape 
patch type EBG structure, the EBG structure depicted in Figure 
4 is kept on the surface of the schematic shown in Figure 2. 

The schematic employed to determine the mutual coupling in 
the presence of U-shape EBG structure is depicted in Figure 6.  

 

 
Fig. 5.  Schematic of PMAA. 

 
Fig. 6.  Schematic of arrangement of elements of PMAA for the 
measurement of mutual coupling. 

IV. FABRICATED MICROSTRIP ANTENNA ARRAYS  

Figures 7-10 show photographs of the fabricated antenna 
arrays. 

 

  

Fig. 7.  Photograph of CMAA. 

 

  

Fig. 8.  Photograph of CMAA elements arrangement for mutual coupling 
measurement. 

 

 
(a) 

 
(b) 

Fig. 9.  Photograph of PMAA, (a) Front view, (b) back view. 

 

 
(a) 

 
(b) 

Fig. 10.  Photograph of PMAA elements arrangement for mutual coupling 
measurement. (a) Front view, (b) back view. 



Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3470-3474 3472 
 

www.etasr.com Rao et al.: Study of Four Element Microstrip Antenna Array Using Patch Type Electromagnetic Band …  

 

V. MEASURED RESULTS  

The performances of CMAA and PMAA are judged in 
terms of bandwidth, return loss, resonant frequency, mutual 
coupling, gain, forward power, back lobe radiation, front to 
back ratio (FBR) and virtual size reduction. Figures 11, 12 and 
13 depict the graphs of return loss and mutual coupling versus 
frequency of CMAA.  

 

Fig. 11.  Graph of return loss and mutual coupling–S21 versus CMAA 
frequency.  

 

Fig. 12.  Graph of return loss and mutual coupling–S31 versus CMAA 
frequency. 

 

Fig. 13.  Graph of return loss and mutual coupling–S41 versus CMAA 
frequency. 

Figures 11, 12 and 13 indicate that CMAA is resonating at 
5.53GHz and producing a return loss of -21.06dB. The mutual 
coupling values measured at the resonant frequency of 
5.53GHz of CMAA are equal to S21=-16.95dB, S31=-14.22dB 
and S41=-17.30dB respectively. These values of mutual 
coupling plots are considered to be very high and need to be 

decreased. Another result that can be extracted from Figures 
11-13 is that the graphs of return loss and mutual coupling are 
overlapping. This implies there is an interference level between 
the transmitting antenna 1 and the receiving antennas 2-4. 
Parameter bandwidth can be determined from the return loss 
graph in Figures 11-13. Bandwidth is calculated by subtracting 
the lower frequency from the upper frequency where the return 
loss is crossing the -10dB value. Hence the bandwidth of 
CMAA is equal to 273MHz. Bandwidth can be expressed in 
terms of percentage as:  

Bandwidth	%� =	 �����������������	��������� × 100 (1) 

Hence substituting the relevant parameters in (1), the 
bandwidth (%) of CMAA is equal to 4.89%. Figures 14, 15 and 
16 depict the graphs of return loss and mutual coupling versus 
frequency of PMAA. Figures 14-16 depict that PMAA is 
resonating at the same fundamental frequency with CMAA i.e. 
at 5.53GHz. Additionally, PMAA is resonating at single 
frequency. The total bandwidth produced by PMAA is very 
high and equal to 6.05GHz. In terms of bandwidth (%), it is 
equal to 109.45%. Therefore, in terms of bandwidth (%) 
PMAA is a better candidate than CMAA, because PMAA is 
producing enhanced bandwidth (%) compared to CMAA, 
which is producing narrow bandwidth of 4.89%. 

 

Fig. 14.  Plot of return loss and mutual coupling–S21 versus PMAA 
frequency 

 

Fig. 15.  Plot of return loss and mutual coupling–S31 versus PMAA 
frequency. 

Information about the mutual coupling coefficients of 
PMAA are obtained from Figures 14, 15 and 16. At resonant 

1 2 3 4 5 6 7

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Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3470-3474 3473 
 

www.etasr.com Rao et al.: Study of Four Element Microstrip Antenna Array Using Patch Type Electromagnetic Band …  

 

frequency of 5.53GHz, the mutual coupling values of PMAA 
are equal to S21=-31.44dB, S31=-36.41dB and S41=-31.62dB 
respectively. Thus in the presence of U-shape patch type EBG 
structure, the values of mutual coupling coefficients are 
decreased. Moreover, the plots of mutual coupling and return 
loss are no more crossing each other at the resonant frequency 
of 5.53Hz. This implies that the amount of interference 
between the antenna element 1 and the antenna elements 2, 3 
and 4 is considerably reduced. Reduction of mutual coupling 
confirms that PMAA is performing better than CMAA in terms 
of mutual coupling.  

 

Fig. 16.  Plot of return loss and mutual coupling–S41 versus PMAA 
frequency. 

The parameter Gain is calculated by (2): 

# = 20log() *
+,-
. / + 10log()

12
13 − #5   (2) 

where Pt is the transmitted power, Pr is the received power, R 

is the distance between the transmitting and the receiving 

antennas, λ is the wavelength at the resonant frequency of 

5.53GHz, and Gt is the gain of the transmitting antenna, given 

by (3): 

#5 = 10log() #6    (3) 
#6 =	7,89.:       (4) 

where α and b are the length and width of the standard 
pyramidal horn antenna used as the transmitting antenna. 
Dimensions α and b are equal to 24cm and 14cm respectively. 
The distance between the transmitting antenna (standard horn 
antenna) and the receiving antenna is given by (5): 

; ≥ 7=
:

.        (5) 

where D is the larger dimension of the transmitting antenna 
equal to 24cm. The value of R=71.86m. 

The transmitted and received powers in the case of CMAA 
are equal to 8.7µW and 12.414nW respectively. Substituting 
these values in (1), the gain of CMAA becomes equal to 
6.81dB. In the case of PMAA, the transmitted and received 
powers are equal to 8.7µW and 0.279µW. Substituting into (1), 
the gain of PMAA is 20.33dB. Hence with the introduction of 
U-shape patch type EBG structure, the gain of PMAA is 
increased, hence PMAA is a better antenna compared to 
CMAA regarding gain. Figure 17 shows the radiation plot of 
CMAA and PMAA.  

 

Fig. 17.  Radiation plot of CMAA and PMAA.  

Using the radiation pattern, the amount of forward and 
backward power radiated is determined. To sketch the radiation 
pattern, the standard pyramidal horn antenna is employed as 
transmitting antenna and CMAA and PMAA as receiving 
antennas. The radiation pattern is plotted for angle from 0

0
 to 

360
0
 in a polar plot. The forward power radiated is measured at 

90
0
 and the backward power at 270

0
. Initially considering 

CMAA, the forward and backward powers measured are equal 
to -2 and -4.5dB respectively. The corresponding powers 
radiated by PMAA are -0.5 and -8dB respectively. We see that 
PMAA is radiating increased power in the forward direction 
and lesser power in the backward direction compared to 
CMAA. Hence PMAA is a better radiator than CMAA in terms 
of forward and backward powers. Parameter FBR is calculated 
by subtracting the backward power from the forward power. 
The FBR values of the microstrip antenna arrays CMAA and 
PMAA are equal to 2.5 and 7.5dB respectively. The FBR value 
of PMAA is greater than that of CMAA. This confirms that 
PMAA is a better antenna than CMAA in terms of FBR 
parameter. Tables II and III depict the comparison of measured 
results of CMAA and PMAA. 

TABLE II.  SUMMARIZED MEASURED RESULTS 

Antenna 

Type 

Resonant 

Frequency 

(GHz) 

Return 

Loss (dB) 

Band 

width 

(MHz) 

Band 

width 

(%) 

Gain 

(dB) 

CMAA 5.53 -21.06 273 4.89 6.81 

PMAA 5.53 -26.12 6050 109.45 20.33 

TABLE III.  SUMMARIZED MEASURED RESULTS 

Antenna Type FBR S21 (dB) S31 (dB) S41 (dB) 

CMAA 2.5 -16.95 -14.22 -17.30 

PMAA 7.5 -31.44 -36.41 -31.62 

 
After comparing the performances of CMAA and PMAA, 

we can say that PMAA outperforms CMAA. It is producing 
enhanced bandwidth, higher gain, better reduction in mutual 
coupling and superior radiation characteristics compared to its 
counterpart. 

VI. CONLUSIONS 

In this paper, a four element microstrip antenna array 
loaded with U-shape patch type EBG structure was 

1 2 3 4 5 6 7 8

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-10
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-10
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3

 CMAA

 PMAA



Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3470-3474 3474 
 

www.etasr.com Rao et al.: Study of Four Element Microstrip Antenna Array Using Patch Type Electromagnetic Band …  

 

investigated. Conventional and proposed microstrip antenna 
arrays were designed and fabricated successfully. The two 
dimensional EBG structure plays a prominent role in reducing 
the mutual coupling between the radiating patches below  
-20dB level. Furthermore, increase in gain by 13.52dB is also 
obtained. The overall bandwidth (%) of PMAA is increased to 
109.45%. Measured results of front and backward power 
confirm that the radiation properties of PMAA are enhanced 
compared to CMAA. 

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