International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 8, August 2013
ISSN 2319 - 4847
Effects of Mutual Coupling on Various
Parameters of Two Element Circular Patch
Microstrip Antenna Array
Sonam Aggarwal1, Anupma Marwaha2
1
M. Tech Research Scholar, ECE Department, SLIET Longowal
Associate Professor, ECE Department, SLIET Longowal, PUNJAB -148 106 INDIA
2
Abstract
The aim of this investigation was to improve the performance of a microstrip antenna array by varying the mutual coupling in
patch elements. This array was considered as a first step to design an adaptive microstrip antenna for different application in
phased array radar and radio communication. The patch distribution structure used in this experiment allowed a great
improvement of gain and directivity. Patch is designed on Triolein dielectric substrate material with dielectric constant 3.2 and
frequency range is 8-10 GHz. The simulation has been performed by using FEM based HFSS software to compute performance
of microstrip patch antenna
Keywords: circular patch, Finite Element Method, HFSS, UMTS, Array antenna.
1. Introduction
The term “microstrip” comes because the thickness of this metallic strip is in micro- meter range. Microstrip patch
antennas are popular, because they have some advantages due to their conformal and simple planar structure. A vast
research is oriented on the investigation of various aspects of microstrip antennas .The key features of a microstrip
antenna are relative ease of construction, light weight, low cost and either conformability to the mounting surface or, at
least, an extremely thin protrusion from the surface.
In the microstrip array, elements can be fed by a single line or by multiple lines in a feed network arrangement. Based on
their feeding methods, arrays are classified as:
• Series feed network
• T-shaped corporate feed network
Series-feed microstrip array is formed by interconnecting all the elements with high impedance transmission line and
feeding the power at the first element. Because the feed arrangement is compact the line losses associated with this type of
array are lower than those of the corporate-feed type. The main limitation in series-feed arrays is the large variation of the
impedance and beam-pointing direction over a band of frequencies.
The corporate-feed network is used to provide power splits of 2n (i.e. n = 2; 4; 8; 16; etc.). This is accomplished by using
either tapered lines or using quarter wavelength impedance transformers. In this paper the patch elements are connected
by using the quarter wavelength impedance transformer method.
Corporate-feed arrays are general and versatile. This method has more control of the feed of each element and is ideal for
scanning phased arrays, multiband arrays. Thus it provides better directivity as well as radiation efficiency and reduce the
beam fluctuations over a band of frequencies compared to the series feed array .The phase of each element can be
controlled by using phase shifters while amplitude can be adjusted using either amplifiers or attenuators.
2. Introduction to Coupling Between Two Radiating Elements
The electromagnetic interferences between radiating elements in a printed antenna array, is expressed by the modification
of the surface currents distribution. This phenomenon, called coupling, depends on the antenna type and the distance
between its elements. The coupling between two printed periodical antennas has a great importance in the design of
antennas arrays, because it may cause a change in the radiation pattern. The current flowing in each antenna induces
currents in the all other antennas, whatever they are supplied or not. The mutual coupling is due to the simultaneous
effects of radiation in free space and the propagation of surface waves. This is an important criterion which should be
considered while calculating array characteristics. The theoretical calculation of mutual coupling depends on the antenna
type and the distance between its elements. Different methods have been presented to calculate the coupling coefficient
between microstrip antennas. The effect of mutual coupling is serious if the element spacing is small. It will affect the
antenna array mainly in the following ways:
1. Change the array radiation pattern
2. Change the array manifold (the received element voltages)
3. Change the matching characteristic of the antenna elements (change the input impedances)
Volume 2, Issue 8, August 2013
Page 91
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 8, August 2013
ISSN 2319 - 4847
3. Design Requirements for Patch Antenna
The selection of appropriate design parameters is prerequisite for performance evaluation of the designed models. The
radiation performance can be improved by using proper design structures. The use of high permittivity substrates can
miniaturize microstrip antenna size. Thick substrates with lower range of dielectric offer better efficiency, and wide
bandwidth but it requires larger element size. Microstrip antenna with superconducting patch on uniaxial substrate gives
high radiation efficiency and gain in millimeter wave length. The width discontinuities in a microstrip patch reduces the
length of resonating microstrip antenna and radiation efficiency as well. Different radar systems such as synthetic
aperture radar (SAR), shuttle imaging radar, remote sensing radars, and other wireless communication systems operate in
L, C and X bands.
The circular patches are designed on dielectric substrate material with dielectric constant =3.2.The two elements circular
patch antenna array is designed and simulated using FEM based HFSS. HFSS is a high-performance full-wave
electromagnetic (EM) field simulator for arbitrary 3D volumetric passive device modeling that takes advantage of the
familiar Microsoft Windows graphical user interface.
4. Circular Patch Element
The most popular configuration among the patches is the circular patch or disk because for the circular patch elements
there is one degree of freedom to control. Thus it is more convenient to design as well as to control the radiation pattern
of the circular patch element.
Table 1 – Specification of designing patch antenna array
In the Fig 1 the antenna has been designed shows the model of single patch antenna with edge feed line. The quarter
wavelength transformer method is used to match the impedance of the patch element with the transmission line.
Fig 1- Design of patch antenna array having less coupling between patch elements
A model was created with less gap between patch elements as in figure 1.
Fig 2 –Design of patch antenna array having more coupling between elements
The model was formed by taking gap between patches is 1.1 cm as shown in figure 2.
5. Simulation Results
XY Plot 5
HFSSDesign1
0.00
ANSOFT
Curve Info
dB(St(Circle1_T1,Circle1_T1))
Setup1 : Sweep
d B ( S t ( C i r c le 1 _ T 1 , C i r c le 1 _ T 1 ) )
-5.00
-10.00
-15.00
-20.00
-25.00
5.0 0
6.00
7.00
8.00
9.0 0
10.00
Freq [GHz]
Fig 3-Return loss of circular microstrip patch antenna array having less coupling factor
Volume 2, Issue 8, August 2013
Page 92
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 8, August 2013
ISSN 2319 - 4847
From the diagram it has been observed that value of return loss is -22dB.This parameter is determined that how well
devices are matched. A match is good if return loss is high in negative value
Fig 4 - 2D Gain of two patches antenna array having less coupling factor
The gain of the antenna is the quantity which describes the performance of the antenna or the capability to concentrate
energy through a direction to give a better picture of the radiation performance. Here total gain of 7 dB has been gained
Fig 5 -3D radiation pattern of antenna array
This diagram demonstrates the two lobes with angle between them which can be used in phased array radar application.
XY Plot 1
HFSSDesign1
0.00
ANSOFT
Curve In fo
dB(St(Cir cle1_T1,Cir cle1_T1))
Setup1 : Sw eep
d B (S t (C i rc le 1 _ T 1 , C ir c l e 1 _ T 1 ))
-5.00
-10.00
-15.00
-20.00
-25.00
5.00
6.00
7.00
8.00
9.00
10.00
Freq [GHz]
Fig 6- Return loss of two element patch circular microstrip array having more coupling factor.
From the diagram it has been observed that value of return loss is -25dB.
Fig 7 - 2D Gain of two patches antenna array having more coupling factor
This diagram shows the gain value of 6.06 dB.
Volume 2, Issue 8, August 2013
Page 93
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 8, August 2013
ISSN 2319 - 4847
Fig 8 - 3D Radiation pattern of two element patch array with more mutual coupling between patch elements
This diagram demonstrates that the antenna arrays with various lobes means it radiates in different direction. With this
merit of omnidirectional this can be used in radio communication.
5. Conclusion
The experiments performed to have allowed performances of our microstrip array antenna array by varying mutual
coupling by decreasing or increasing the distance between patch elements. The simulation results show return loss of -22
dB and the array is characterized by a directive antenna a gain of 7.01dB.The array antenna having less coupling in patch
elements can use in phased array radar. The antenna with less coupling having return loss -23 dB and have
omnidirectional radiation pattern. Value of gain is 6.06 Db. This array antenna can use in radio communication specially
in walkie-talkie radios because the gain is also between 2 – 9 dB
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