tablasantans

COMPACT MICROSTRIP ANTENNA BASED ON
FRACTAL METASURFACE WITH LOW RADAR
CROSS SECTION AND WIDE BANDWIDTH
Evelyn Bustos (992), Pamela Guerrero (924), Jhonny Asqui (935)
evelyn.bustos@espoch.edu.ec pamela.guerrero@espoch.edu.ec silvio.asqui@espoch.edu
Escuela de Ingenierı́a en Electrónica Telecomunicaciones y Redes - FIE - ESPOCH
Riobamba - Ecuador
Abstract.- The compact antenna with wide
bandwidth is important. In this paper, we have
studied the microstrip slot antenna for wireless
application based on the fractal structure which
has covered 2.6–4.1 GHz (85 % bandwidth).
The circular slot antenna with four rectangular
slots is considered and then six dual rings are
added to the antenna. Finally, for improving
the matching a disk is placed in the central part
of the slot. The fractal model has been considered for low RCS, for improving the bandwidth,
for amending the matching of the antenna by
controlling the current distribution and it is
modified for C-band application.
controlling the antenna surface current distribution.[4]
Furthermore, as mentioned the fractal method is developed as a conventional method for RCS reduction while
the fractal shapes are known as self-similar shapes, and
are usually found in galaxies, cloud boundaries, mountain ranges, coastlines, snowflakes, trees, and leaves
and fractal method have been examined for various
applications like antenna and the absorbers based on
metamaterial . Recently, the fractal shapes are more
attractive to reflect-array and monopole antenna to
reduce the RCS. The microstrip circular slot antenna
with a straight feed line is selected as our basic structure. We have investigated that we can obtain wider
bandwidth with a great enhancement only by adding
rectangular slot and the dual ring structure[5]. Finally,
the circular disk is located in the central part of the
slot for improving the matching of the antenna and
the fractal technique is used to reduce the radar cross
section.
These aforementioned references have been presented
to improve the problem of the bandwidth. Fractal
shapes have the interesting self-similarity property.
Briefly speaking, self-similarity can be described as
the replication of the geometry of the structure at a
different scale within the same structure. Thus, the
self-similarity of fractal structure results in a multiband or wideband behavior. At the same time, fractal
shapes can be used to design the antenna and FSS for
reducing the sizes of them[6].
Although the dual-band or multi-band FSS can be
achieved based on the different geometry lengths, the
bandwidth is still limited. To resolve this problem,
the wideband FSS and high-order FSS are developed
for a good performance. Traditionally, a wideband or
multipole FSS can be obtained by cascading the multifirst-order FSSs with the quarter wavelength interval
between each other[7].
I. INTRODUCTION
The microstrip antenna is a conventional kind of
antenna for radar application which it is used for various applications such as communication system, medical application, mobile services and radar systems in
missile .In addition, the radar cross section (RCS) of
the antenna is known as an important factor for some
of these applications. The radar cross section (RCS) is
noticed for stealth application by coating the surface
of an aircraft[1] .
Exactly, the RCS is a parameter for measuring
of the object detection and the low RCS means that
an object can find hard by radar systems. Consequently, it is attractive for stealth application . On the
other hand, nowadays antennas with low RCS have
been noticed while the fractal technique is one of the
main methods for this goal[2] . Moreover, the ultrawideband antenna with low RCS has been considered
such Vivaldi antenna , the monopole antenna with
small ground [3].
The patch antenna is more considered for various
microwave applications or for reducing the RCS. The
loads have been combined by Yagi antenna and patch
feed for decreasing of the RCS . Moreover, the metasurface and frequency selective surface recently have
been studied for low radar cross section and circular polarization application, simultaneously based on
II.PROPOSED ANTENNA
The microstrip slot antenna has been developed
based on feed coupling with the ground layer. The
various shapes of the slot antenna like rectangular
and circular formation have been studied during the
past decades [8]. Moreover, the metamaterial or other
1
structures have been considered for different qualifications such as circular polarization or wider bandwidt
[9]. Fig. 1 shows the antenna designing step from a
simple slot to the final antenna.
The geometry of the antenna is presented in Fig. 2(a)
and (b) for the ground layer and the feed line, respectively, where the feed line is connected to a 50 ohm
SMA connector. As shown here, the main slot is made
in the circular shape with 4 small rectangular slots
which they are rotated 45. Then, the six dual ring
structures are added to the antenna as parasitic loads
and finally, a disk is placed at the center for matching.
provided wider bandwidth and lower RCS.
In addition, the RCS is improved at the resonance frequency and the antenna gain is more than the similar
research with high efficiency. Exactly, this antenna has
a compact size in comparison with the other suggested
model because we have combined the metasurface layer
inside of the ground layer.
The total size of the antenna is 40x40 mm2. It is
designed on FR4 with the thickness of 1.6 mm as a
low cost substrate with the permittivity of 4.3 and loss
tangent of 0.02. The antenna all dimensions are a =
40 mm, b = 3.65 mm, c = 4 mm, d0 = 27 mm, d1 =
7.8 mm, d2 = 5.8 mm, d3 = 5.2 mm, w = 3 mm and l
= 20 mm.
Apparently, we have compounded a metasurface
to the conventional microstrip slot antenna which is
Figure 1: The four steps in antenna design from slot antenna to slot antenna with the fractal ring.
Figure 2: The antenna’s geometry (a) the ground layer with parasitic elements, (b) the feed line geometry.
III.SIMULATION OF ANTENNA
Fig.4 .
The simulated tool is using Ansoft Designer Fig.3.
Besides, in the simulator program can obtain several
graphic as the radiation pattern , impedance should in
this case have zero imaginary part, and 50 in the real
The result indicates that the bandwidth is about part, which results are shown in Fig.5.
1.5Ghz,from 2,6 to 4.1GHz.which results are shown in
2
The antenna radiation pattern for Phi = 0 and Phi = polarization. Fig.6 shows the antenna 2D radiation
90 at 3.1 GHz and slot is known for their bi-directional pattern for simulation and experimental.
radiation pattern in Phi = 0 and Omnidirectional pattern in phi = 90 where the antenna shows low cross
Figure 3: Simulation of antenna in ansoft designer
Figure 4: The result indicates that the bandwidth
3
Figure 5: Diagram real and imaginary impedance. We can see the diagram where the imaginary part is
aproximately zero at 3.1 GHz.
Figure 6: Radiation Pattern
IV. IMPLEMENTATION AND RESULTS
rect results, the antenna was deployed in FR4, taking
into account the design measures within the simulation,
Fig.7. presents the final structure.
Once the simulation was done and to obtain cor-
4
Figure 7: Top and bottom side
The results were obtained using the signal genera- distance and obtained the following gain value of 49dB
tor, which is connected to the antenna and a spectrum at the operating frequency of 3.1GHz.Therefore, it is
analyzer where the receiver and transmitter are shown considered that the antenna works correctly.
in Fig.8. The antenna was located at a considerable
Figure 8: Measured results
In addition, gain values in dB were taken at frequencies from 2.43 Ghz to 3.8 Ghz.The data obtained
are shown in Fig.9.This graphic indicates that there
are frequencies with higher and lower gain in which the
antenna, you can also work. Through the use of Mat-
lab, was obtained from the graph of the frequency with
respect to the gain of the antenna.The figure previous
indicates that relationship, having some similarity with
that generated in the simulation in Ansoft Designer.
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Figure 9: Frequency vs. Gain
The measurement of the antenna was made by varying the theta and phi angles, this variation indicates
the radiation that the antenna, in Fig.10 these data
are observed with respect to the phi angle.
Figure 10: Radiation phi angle
V. CONCLUSION
of a high precision especially if it works with high frequencies where the length of the antenna is going to be
specified in Micrometers.
The length of the antenna is inversely proportional
to the frequency of operation that is why the order of
the Ghz the antenna has a more short structure.
The equipment used for the testing and analysis
of our antennas were a Spectrum Master of the High
Performance Handheld Spectrum Analyzer and a signal generator which to be working in perfect condition
give us an analysis with low level of error.
After implementing the transmitting and receiving antenna, it was obtained as a result that the frequency of operation with which the antenna worked is
1.4 GHz compared to the frequency of 1.5 Ghz with
which work was done in simulations. Concluding that
the frequency of operation had a phase shift of 0.1 Ghz.
In addition to achieving an antenna sufficiently efficient it can be seen that the materials with which
they were manufactured are of low monetary cost but
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VI. RECOMMENDATION
with reduced radar cross section. Prog Electromagn
Res 2009;96:299–308.
To obtain a correct gain of the antennas, the equipment must be configured correctly, in the different op[5] W. S. Chen and K. Y. Ku, “Bandwidth enhancetions such as reference level, scale, automatic attention, ment of open slot antenna for UWB applications,”
displacement, units, central frequency, Atten LvI and Microw. Opt. Technol. Lett., vol. 50, no. 2, pp.
RL.
438–439, 2008.
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