The theoretical study of the effect of parasitic element to increase the bandwidth for ring micro strip antenna

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6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 9, September (2014), pp. 09-13 © IAEME
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ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 5, Issue 9, September (2014), pp. 09-13
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THE THEORETICAL STUDY OF THE EFFECT OF PARASITIC ELEMENT
TO INCREASE THE BANDWIDTH FOR RING MICRO-STRIP ANTENNA
Ambikesh Tripathi Raj Kumar Tiwari*
Department of Physics Electronics, Dr. R.M.L. Avadh University, Faizabad (U.P.)
9
ABSTRACT
Micro-strip patches are the new generation of antennas due to their many attractive features,
including low profile, lightweight, have simple geometries, are inexpensive to fabricate and can be
easily made conformal to the host body. In the present theoretical investigation regarding Ring
Micro-Strip Antenna we have investigated the effect of parasitic elements to improve the bandwidth
of Ring Patch Antenna.
Keywords: Bandwidth, Fringing Field, Impedance Matching, Parasitic Element, Ring Microstrip
Antenna.
I. INTRODUCTION
In future mobile communication systems requires low profile, lightweight, as well as the ease
in which these radiators can be integrated with photonic and micro wave monolithic integrated
circuit (MMIC) technologies [1]. One of the major drawback of the microstrip antenna is its narrow
band-width. The bandwidth of a patch antenna can be substantially increased through the use of thick
substrate. The grounded dielectric substrate supports surface wave modes, however, it lowers the
antenna efficiency. Various methods have been investigated recently for improving the narrow
bandwidth of microstrip antennas. Well known methods are addition of a parasitic patch on the top
of the original patch [2], proximity coupling of feed line to the patch antenna [3], and impedance
matching of input port by stub lines [4]. Among these techniques the effect of parasitic elements
receives much more attention, mainly due to additional advantage of adjusting the beam width, gain,
and efficiency by the parasitic patch [5]. Another approach for improving the bandwidth
performance of patch antenna is to add parasitic elements to the antenna structure [6, 7]. This reduces
the impedance variation of the antenna with frequency which enhances bandwidth performance.
Parasitic elements are designed to resonate close to the resonant frequency of the driven radiator
element, leading to a desirable tuned response. It is also called double-resonance phenomenon
technique [8].

2. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 9, September (2014), pp. 09-13 © IAEME
10
II. THEORETICAL ANALYSIS
The element supplying power directly from source (i.e. Transmitter) usually through
transmission line is called as driven element. But a parasitic element is not fed directly instead
parasitic element drives power by radiation from nearby driven element. In other words, parasitic
element obtains power solely through electromagnetic coupling with a driven element because of its
proximity to that driven element. There are various methods for dealing with the analysis of the
parasitic elements placed close to a driven element. One approach to the analysis is to compute the
capacitance that exists between the parasitic and the driven antenna elements. Consider the ring
microstrip geometry as shown in fig. 1.
Fig. 1: Geometry of the ring patch antenna coupled with a parasitic element
The capacitances can be expressed in terms of even and odd mode values for the two modes
of propagation for rectangular patch [9]. The distribution of the capacitances of the ring microstrip is
shown in Fig. 2 for the two modes.
Fig. 2: Distribution of capacitances of (a) even mode (b) Odd mode propagation

3. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 9, September (2014), pp. 09-13 © IAEME
The even mode capacitance shown in fig. 2 (a) can be divided into three categories. Thus
Ceven = Cp + Cf + C'f ……………(1)
Where Cp is the parallel plate capacitance between the strip and the ground plane, Cf is the
fringing capacitance obtained from uncoupled microstrip and Cf
11
' is the fringing capacitance due to
the presence of another microstrip. These capacitances have been obtained for a ring micro-strip
patch as given below.
C
a
H p r
= 2 Î Î 2 0 .................( )
.......... .......... .......... ...( 3 )
reff
1 K
0
2
−
Î
=
cZ C p
f
C
.......... .......... ...( 4 )
H

5. 1 tanh 10
'
r
reff
S
H
S
A
f
C
f
C
Î
Î
+
=
where c, Îr eff and Zo are the speed of light in free space, the effective dielectric constant of the
substrate and the characteristics impedance of the ring microstrip, respectively. The expression of C'f
is obtained empirically such that the resulting value of even-mode capacitance is comparable with
numerical results. The value of A in the expression (6.4) for C'f is given by
A = exp [-0.1 exp (2.33-5.06 a/H)] .................(5)
The odd mode capacitance, shown in Fig. 6.2 (b) is expressed by –
Codd = Cp + Cf + Cgd + Cga .................(6)
where Cga and Cgd are the capacitances for the fringing fields across the gap in the air region and in
the substrate region, respectively.
Once the capacitances are known, the impedances for the even and odd modes are computed
separately using the cavity model. The resultant input impedance of the system is given by-
Zin = Zin, even + Zin, odd ..................(7)
The impedance bandwidth is then found by calculating the input impedance at each
frequency. The antenna bandwidth is a width (i.e. range) of frequency over which the antenna
maintains certain required characteristics like gain, front to back ratio or S.W.R. pattern (shape or
direction), polarization and impedance. In general, the bandwidth of an antenna, as said, mainly
depends on its two characteristics e.g. impedance and pattern. The band-width of microstrip antenna
is defined as, the frequency range over which the value of the input VSWR increases from unity to a
tolerate limit values. The bandwidth of microstrip antenna [10] is given by

6. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 9, September (2014), pp. 09-13 © IAEME
12
BW
s
Q s T
=
− 1
......................(8)
Where ‘s’ is the distance between two patches under consideration.
Using parasitic elements to improve the match of the radiator to the feed line may increase
the bandwidth of ring microstrip antenna. One technique is to add parasitic elements, indeed, the
coupling between the driven structure and parasitic elements odds capacitance to the structure. The
configuration of coupled parasitic element structure antennas are classified into two categories- edge-coupled
structure and capacitively fed structure, respectively.
III. EDGE-COUPLING STRUCTURE ANTENNAS
The ring microstrip antenna geometry with a parasitic edge coupled element is shown in fig. 3
Fig. 3: Antenna geometry of a RMSA using edge coupled parasitic elements
Various experiments were carried out in [11] to study the effect of gap width on the
performance of antenna structure. To further increase the bandwidth, the parasitic element having
unequal radius (a1 ¹ a2). This produces a triple-resonance phenomenon and widens the bandwidth.
The technique of edge-coupling structure of Ring Micro-Strip Antenna is a popular method for
enhancing the impedance bandwidth.
IV. RESULTS AND DISCUSSION
Thus in the present theoretical investigation regarding Ring Micro-Strip Antenna, we have
investigated the technique of widening the bandwidth of low-profile ring microstrip antenna. The
widely used technique consists of adding parasitic elements to the antenna structure. In future this
research work is much useful for increasing the bandwidth of ring microstrip antenna for nano-dimension.
V. REFERENCES
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[3] D.P. Pozar and B. Kaufman, Electron, Lett, Vol. 23, pp: 368-369, 1987.
[4] H.F. Pues and A.R. van de Capelle, IEEE Trans. Antennas Propagat, Vol. 37, pp: 1345-1354,
1989.
[5] R.Q. Lee and K.F. Lee, Electron. Lett. Vol. 24, pp: 656-658, 1988.

7. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 9, September (2014), pp. 09-13 © IAEME
[6] P. Bhartia, K.V. S. Rao and R.S. Tomar, Narwood, MA: Artech House, 1991.
[7] W.C. Lo and S.W. Lee, Antenna Handbook, New York, Van Nostrand, 1993.
[8] K. Hirisawa and M. Haneishi, Artech House, Bostan, 1992.
[9] R. Garg, Inst. J. Electronics, Vol. 47, No. 6, pp: 587-591, 1979.
[10] Derneryd, A.G., IEEE Trans. on Antennas and Propagation Vol. Ap-27, pp; 660-664, 1979.
[11] G. Kumar and K.C. Gupta, IEEE Trans. Ant. Prop., Vol. AP-32, No. 12, pp: 1375-1379,
13
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