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1. 1522 PIERS Proceedings, Kuala Lumpur, MALAYSIA, March 27–30, 2012
Performance Evaluation of Three Rectangular Patch Element Array
Antenna Conformed on Small Radius Cylindrical Surface
Emad S. Ahmed and Jawad K. Ali
Department of Electrical and Electronic Engineering, University of Technology, Baghdad, Iraq
Abstract— The cylindrical geometry can offer certain desirable antenna characteristics that
are not provided by planar elements. In this paper, a three-element cylindrical conformal array
antenna has been presented as a candidate for use in wireless communications and Radio Fre-
quency Identification (RFID). Each element in the array is a microstrip fed rectangular patch
antenna designed to resonate at 2.4 GHz. Once the desired results were obtained for a single
element, each element in the conformal cylindrical array has been then designed using the same
dimensions and parameters. Modeling and performance evaluation of the array has been carried
out using the commercially available electromagnetic software CST Studio SuiteT M 2009. Sim-
ulations have been conducted to study the performance of the proposed conformal array as well
as the effects of small radius cylinder on mutual coupling and the radiation pattern of the array.
The cylindrical radii in consideration are of about one quarter wavelengths or slightly more. The
radius of cylinder used in simulation is taken to be 0.24λ and 0.32λ. Compared with the existing
cylindrical conformal antenna, the proposed array antenna possesses a reduction in cylindrical
structure radius with acceptable ominidirectionality and gain needed for wireless communications
and RFID applications.
1. INTRODUCTION
Miniaturization in the integrated circuit technology and advancement in signal and data processing
have opened prospects for wide spectrum of applications which uses densely packed terminals
placed in little volume. That is why such applications depend on availability of conformal shaped
antennas, ensuring required directions of radio wave propagation and enabling hidden terminal
mounting. The range of applications spans from sensors goes through wireless access modes and
then up to modern miniaturized spacecraft [1].
One of the most important innovations in modern antenna technology is the conformal antenna
array. Conformal arrays have good potential for application in aerospace vehicles with excel-
lent aerodynamic characteristics. Cylindrical antenna arrays have attracted the greatest attention
amongst conformal antennas and their applications include mobile cellular base stations, airborne
radar and mobile satellite communication terminals [2, 3].
Microstrip antennas are often used because of their thin profile, light weight and low cost.
Furthermore, they can be made conformal to the structure. When the radius of the curved structure
is large, the antenna can be analyzed as the planar one. However, for structure with smaller radii,
more rigorous analysis methods should be used. If the antenna has a cylindrical shape, i.e., if one
principal curvature is zero, the antenna can be analyzed as a circular-cylindrical one. In the case
were both principal curvatures are different from zero, the antenna can be analyzed as a spherical
one [4].
The use of cylindrical substrate for microwave design is generally driven by the physical at-
tributes of the system rather than by choice, since the analysis and fabrication are more compli-
cated than for a comparable planar implementation. However, the cylindrical geometry can offer
certain desirable antenna characteristics that are not provided by planar elements. There are also
variety of configurations that can be realized, for example cylindrical conformal patch and slot an-
tennas [5–7], microstrip [8], and coplanar transmission lines [9]. Cylindrical conformal structures,
with radii greater than one half wavelengths, have been proposed for use as prospective candi-
dates for mobile communications systems, cellular base stations, and Telemetry, Teleranging and
Telecommand (TTC) communication that is essential to maintain space missions due to their full
field of view advantage [1, 10, 11].
In this paper, a microstrip fed rectangular patch antenna resonates at 2.4 GHz is considered.
The proposed planar patch antenna is used in array consisting of three equally spaced elements.
The proposed antenna array is conformed on a finite cylindrical substrate of 1.57 mm thickness and
relative permittivity of 2.2. Two different radii for the cylindrical structure are simulated using
CST Microwave Studio simulator. Results obtained on return loss, coupling between elements and
radiation pattern are presented and discussed.
2. Progress In Electromagnetics Research Symposium Proceedings, KL, MALAYSIA, March 27–30, 2012 1523
2. ANTENNA DESIGN AND CONFIGURAIONS
2.1. Single Element Antenna Structure
The configuration of the rectangular patch antenna is shown in Figure 1(a). The patch has been
modeled in CST Studio and its dimensions have been adjusted to resonance at 2.4 GHz. A quarter-
wave transformer was used to match 343 Ω input impedance to a 50 Ω system. The final dimensions
of the entire microstrip patch are given in Table 1. Figure 1(b) shows the return loss response of
the patch element antenna. It can be clearly indicated that the antenna was resonates at 2.4 GHz
with return loss of less than −10 dB within 40 MHz bandwidth.
2.2. The Proposed Conformal Antenna Array Structure
Three patch elements were equally spaced on cylindrical substrate. The substrate material used
for modeling has a thickness of 1.57 mm. The dielectric constant of the substrate is εr = 2.2.
The conductive material in the model is of 70.0 µm thick copper. The radius of the cylinder is
comparable to one quarter wavelength and the height is H = 90 mm. Inside the cylinder there is a
2
0
-2
-4
Return Loss, S11(dB)
-6
-8
-10
-12
-14
-16
-18
2 2.2 2.4 2.6 2.8 3
Frequency, GHz
(a) (b)
Figure 1: (a) The layout of single element patch antenna structure, and (b) is its return loss S11 (dB)
response for single element patch antenna.
Figure 2: A 3-D view of the modeled 3-element array.
Table 1: Antenna dimensions in mm.
W L W1 L1
60 88 41.08 39.03
W2 L2 W3 L3
0.72 24.05 4.84 15
3. 1524 PIERS Proceedings, Kuala Lumpur, MALAYSIA, March 27–30, 2012
continuous ground plane of 70.0 µm thick copper. The model of the antenna array taken from the
simulation software is shown in Figure 2.
3. PERFORMANCE EVALUATION
The cylindrical structure of Figure 2 has been modeled through a commercially available finite
element package CST Studio Suite. Cylinders with radii 30 and 40 mm (0.24 and 0.32λ) have been
analyzed while keeping the rest of the antenna parameters fixed. The simulation results of return
loss of all of the ports of the array and the coupling among the antenna elements are shown in
Figure 3.
From Figure 3, it’s clearly observed that the coupling between elements for 30 mm (0.24λ)
radius cylinder is about −1 dB, while for cylinder of 40 mm (0.32λ) radius, the coupling is less than
−18 dB. The small radius of the cylinder results in decreasing the spacing between the elements so
the mutual coupling between elements is increased.
Simulated radiation patterns at 2.4 GHz for single element and 3-element array are illustrated
in Figure 4.
The radiation patterns are significantly affected. In the elevation direction, the radiation pattern
10 10
0 0
S11 -10 S11
-10 S22
S22
S33 -20 S33
-20 S21
Return Loss, dB
Return Loss, dB
S21
S31 -30 S31
-30
S32 S32
-40
-40
-50
-50
-60
-60 R=40 mm
-70
R=30 mm
-70 -80
-80 -90
2 2.2 2.4 2.6 2.8 3 2 2.2 2.4 2.6 2.8 3
frequency, GHz Frequency, GHz
Figure 3: Simulated coupling of the 3-element array conformed on cylinders with radii of 30 mm (0.24λ) and
40 mm (0.32λ).
E θ plane H φ plane E θ plane H φ plane
(a) (b)
Figure 4: Radiation patterns: (a) for element in cylindrical array, the radius of cylinder is R = 30 mm
(0.24λ) and (b) radius of cylinder is R = 40 mm (0.32λ).
4. Progress In Electromagnetics Research Symposium Proceedings, KL, MALAYSIA, March 27–30, 2012 1525
is strongly dependant on the cylinder radius but much less so in the azimuth direction. The E
plane (Eθ ) and H plane (Hφ ) fields, depicted in the figure, reveal that they still have an acceptable
quasi ominidirectional radiation pattern.
4. CONCLUSION
This paper presents detailed performance evaluation concepts of a three rectangular patch element
conformal antenna arrays. There are few issues that should be taken into consideration when
designing such antennas. Firstly the curvature of the cylindrical array affects the radiation pattern
of the antenna and the optimal radius should be found depending on the application on hand.
Secondly the spacing between elements is very important to consider as it affects the level of mutual
coupling in the array. An acceptable mutual coupling was obtained for cylinder radius greater than
one quarter wavelength. The result shows that the resonant frequency is not affected by curvature
however the radiation patterns are significantly affected. The radiation pattern in the elevation
direction is strongly dependant on the cylinder radius but much less so in the azimuth direction.
Simulation results shows that the proposed array antenna possesses an acceptable ominidirectional
radiation pattern needed for most wireless communications and RFID applications.
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