Planar Dipole Antenna with and without Circular Parasitic Element
Osman Ayop1, Mohamad Kamal A.Rahim1 and Thelaha Masri1
1
Wireless Communication Centre,
Faculty of Electrical Engineering,
Universiti teknologi Malaysia,
81310 Skudai Johore Baharu.
[email protected], [email protected], [email protected].
Abstract - This paper describe the design of planar
Dipole Antenna with Circular Parasitic Element. The
comparison between the planar dipole antenna with
and without parasitic element has been presented
followed by a discussion of the design.. The simulation
process was carried out using microwave office and
CST software. These antennas were fabricated using
inexpensive Fire Retardant-4 (FR4) board, using wet
etching techniques. The S11 result shows the operating
frequency is between 2.08 GHz and 3.48 GHz for
planar dipole antenna with parasitic element. For
planar dipole antenna without parasitic element, two
ranges of operating frequency is between and 2.1 GHz
and 3.08 GHz and another one operational frequency
was found at 4.04 GHz and 4.98 GHz.
Keywords: planar Dipole Antenna; Circullar Parasitic
Element; bandwidth enhancement; Band suppression;
1. Introduction
Recent development in wireless communication
systems and its application is advancing rapidly not
only for commercial but also for military purposes.
Wireless technology provides less expensive
alternative and a flexible way for communication. In
term of frequency, the 2.4 GHz ISM band has become
very popular and is now widely used for several
wireless communication standards [1]. The planar
dipole antenna has been used in this project due to the
advantage such as attractive features of low profile,
light weight, easy fabrication and conformability to
mounting host [2]. The idea of microstrip antenna was
first presented in year 1950’s but it only got serious
attention in the 1970’s [3]. However microstrip
antennas inherently have a narrow bandwidth [4]. In
this case, the dipole antenna has been designed to
enhance the bandwidth of the microstrip antenna [5].
The dipole can be defined as two straight wire or
conductor connecting to the feed line. One of the most
commonly used antennas is the half-wavelength
(l=λ/2) dipole. Because its radiation resistance is 73
ohms, which is very near the 75-ohm characteristic
impedance of some transmission line, its matching to
the line is simplified especially at the resonance [6].
Figure 1: Dipole antenna.
The electric and magnetic field components of a
half-wavelength dipole can be obtained by this
formula:
 π

cos cos θ  
iο e − jkr   2


Hφ ≅ j
2πr 
sin θ





(1)
The time-average power density Wav and radiation
intensity U can be written, respectively as:
2
 π

cos cos θ  
2
Io   2
  ≈ η I o sin 3 θ
Wav = η 2 2 
2 2
sin θ
8π r
8π r 





2
(2)
2
 π

cos cos θ  
2
Io   2
  ≈ η I o sin 3 θ
2
U = r Wav = η 2 
sin θ
8π 
8π 2 r 2





2
(3)
The total power radiated Prad can be obtained
using this formula:
Prad = η
Io
8π
2
∫
2π
0

π

 cos cos θ  
2
2
 dy = η I o cos(2π )



sin θ
8π




(4)
The dipole antenna has omni directional radiation
pattern whose two-dimensional pattern is shown
plotted in Figure 2. For the three-dimensional pattern
of Figure 3, a 900 angular sector has been removed to
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illustrate the figure-eight elevation plane pattern
variations.
Figure 4: planar dipole antenna without circular
parasitic element.
Figure 2: 2D Dipole antenna. [2]
The rectangular patch size is chosen after the
optimization. The length and width of the structure are
is 17 mm and 33. The overall size of the antenna is 90
mm x 90 mm with 90 mm x 64 mm ground plane.
2.2 Planar Dipole Antenna with Parasitic
Element
The microstrip dipole antenna with circular
parasitic element has been designed to compare the
performance of the antenna with the previous one.
Figure 5 shows the microstrip dipole antenna with
circular parasitic element.
Figure 3: 3D Dipole antenna. [2]
2. The Design and Construction
The Dipole Antenna with and without Parasitic
element are developed by using inexpensive Fire
Retardant-4 (FR4) board which has 1.6 mm-thick
substrate with relative permittivity 4.6. The wet
etching technique has been used to fabricate the
structure after the optimization of the design.
2.1 Planar Dipole Antenna without Parasitic
Element
The microstrip dipole antenna has been designed
due to the larger bandwidth compared to the
conventional microstrip antenna design. Figure 4
shows the figure of microstrip dipole antenna with the
dimension.
Figure 5: Planar dipole antenna with circular parasitic
element.
The dimensions of the antenna have been shown
in the above figure. The unique property of the antenna
is the circular shape is used instead using the
rectangular shape.
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3. Result and Discussion
Both antennas have been fabricated and measured.
The performances of the structures are evaluated in
term of return loss, S11 and radiation pattern.
3.1 Measurement Result of Planar Dipole
Antenna without Circular Parasitic Element
Figure 6 shows the measurement of return loss
result of the planar dipole antenna without circular
parasitic element.
b) H-plane
Figure 7: Radiation pattern of planar dipole antenna
without circular parasitic element.
3.2 Measurement Result of Planar Dipole
Antenna with Circular Parasitic Element
Figure 6: Measured S11 of planar dipole antenna without
circular parasitic element.
From this result it shows that the operating
frequency has been increased between 2.08 GHz and
3.48 GHz. The operating bandwidth is 1.4 GHz
compared with the previous result of 0.98 GHz
bandwidth.
From this result it shows that the operating
frequency of the antenna is between 2.1 GHz and 3.08
GHz. The second mode appeared at frequency from
4.04 GHz to 4.98 GHz.
Figure 7 below shows the radiation pattern of the
microstrip dipole antenna without circular parasitic
element at 2.4 GHz for both plane.
Figure 8: Measured S11 of planar dipole antenna with
circular parasitic element.
From figure 8 above, the range of operation
frequency of the antenna is from 2.08 GHz to 3.48
GHz which has 1.4 GHz bandwidth.
a) E-plane
Figure 9 shows that the radiation pattern is very
similar with the planar dipole antenna without circular
parasitic element.
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Conclusion
The planar dipole antenna with and without
circular parasitic element has been presented in this
paper. The properties of the antenna such as return loss
and radiation pattern has been discussed. It shows that
by adding the parasitic elements, the return loss of the
antenna has been increased with the same properties of
the radiation pattern.
a) E-plane
Acknowledgement
The authors thanks to the Ministry of Higher
Education (MOSTI) for supporting the research work,
Research Management Centre (RMC) and Wireless
Communication Centre, Universiti Teknologi Malaysia
(WCC, UTM) for the support of paper presentation.
References
b) H-plane
Figure 9: Radiation pattern of planar dipole antenna
with circular parasitic element.
4. Comparison for Planar Dipole antenna
with and without Parasitic Element
The comparison has been made for both antenna
developed in term of S11 and radiation pattern.
Referring from figure 10, the bandwidth of the planar
dipole antenna with circular parasitic element is wider
compared to the planar dipole antenna without circular
parasitic element. The second band which appears to
the antenna without circular parasitic element is
suppressed by adding circular parasitic element at the
original structure.
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Figure 10: Comparison of measured S11 of planar dipole
antenna with and without circular parasitic element.
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