Progress In Electromagnetics Research Symposium Proceedings, Taipei, March 25–28, 2013
147
Analysis of Phase Range Distribution of Different Reflectarray
Elements on Polycrystalline Silicon Cell
A. Selamat1 , N. Misran1, 2 , M. T. Islam1, 2 , and M. F. Mansor1
1
Department of Electrical, Electronic and System Engineering
Universiti Kebangsaan Malaysia, Bangi, Selangor 43600, Malaysia
2
Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia
Bangi, Selangor 43600, Malaysia
Abstract— The bandwidth behavior of reflectarray elements are discussed in this paper to
overcome the intrinsic limitation of narrow bandwidth it offers. This is done by analyzing the
relationship between bandwidth and phasing distribution characteristics of the elements. Five
shapes of elements, i.e., ring, rectangular loop, triangular loop, square loop and ellipse loop have
been investigated. Each element is designed on Kapton sheet positioned on top of a coverglass
layer that protects the silicon layer. Rogers RT/Duroid 5880 dielectric substrate (εr = 2.2 and
tan δ = 0.0009) is used to support the layers above. These elements are designed to operate
at Ku-band frequency range using CST microwave studio. The elements dimension are varied
thus modifies the surface current distribution that leads to variation of phase reflection from the
elements. The relationship of bandwidth performance with the obtained reflection loss of each
element is then investigated. It has been demonstrated from this work that triangular element
can offer the highest static linear phase range about 263◦ , whereas the square element gives the
lowest static linear phase range of 153◦ . The surface area of resonating element has significantly
control the current distribution hence leads the triangular element with the lowest surface area
to has steep phase variation. While square element with greater surface area is shown to exhibit
smoother phase variation with broader bandwidth performance. Moreover, the CST simulation
results also shown that triangular element can operate at two resonant frequencies within Kuband at 12.22 GHz and 14.09 GHz which can be further exploited for satellite and communication
applications.
1. INTRODUCTION
Nowadays, study on reflectarray antenna to replace the conventional parabolic reflector antenna
is becoming a trend. Various advantages including flat surface, light weight and low cost to manufacture have made this antenna the choice of study. However, one major obstacle need to be
faced is the bandwidth limitation. Various studies have been carried out to overcome this problem.
Bandwidth can be increased using two layer grounded array of rings [1], whereas the linearity of
reflection phase response are controlled by the diameter ratio of the ring [2, 5]. Introduction of split
concept into the element has also improved bandwidth significantly [3]. Thus, this paper discusses
the basic design procedure using five different shapes of element that is printed on silicon solar cell
and to study the phase performance of each resonant element.
2. DESIGN METHODOLOGY
The reflectarray elements are designed to be operated at Ku-band with five different shapes comprising rectangular loop, square loop, ellipse loop, triangular loop and ring. Figure 1 shows the
details design for each element used in this experiment. Each design has passed through an optimization process to get the exact nominal value so that all designs are resonated around 14 GHz
frequencies. Table 1 depicted the detail dimensions of each design respectively.
w
x
x
y
x
w
w
y z
z
x
w
x
y z
y
y
z
(a)
(b)
(c)
(d)
(e)
Figure 1: Geometries of (a) ring, (b) ellipse loop, (c) square loop, (d) rectangular loop, (e) triangular loop.
PIERS Proceedings, Taipei, March 25–28, 2013
148
a
b
c
a
d
e
z
f
y
g
x
Figure 2: A 3-D geometrical view.
Table 1: Dimension of each element.
Element/Dimension
Ring
Ellipse loop
Rectangular loop
Square loop
Triangular loop
w (mm)
4
8
9
6.2
x (mm)
3.4
2
5.5
5.8
8
y (mm)
4.5
3
5
5.8
6
z (mm)
3
7
9
8
Table 2: Geometry of each layer.
a
b
c
d
e
f
g
Layer/Dimension
Periodicity
Copper (Top)
Kapton sheet
Silica glass
Silicon Solar Cell
RT/Duroid 5880
Copper (Bottom)
x (mm)
10
10
10
10
10
10
y (mm)
10
10
10
10
10
10
z (mm)
4.246
0.1
0.051
1.52
0.5
1.575
0.5
All the above mentioned copper elements are constructed on top of a Kapton sheet of 0.051 mm
thickness and secured on top of a cover-glass [4] as shown in Figure 2. The 1.52 mm cover-glass
is used to protect a solar cell layer of 0.5 mm thickness situated in-between the silica glass and
RT/Duroid substrate. The Rogers RT/Duroid 5880 substrate layer of 1.575 mm thickness is used
to support all the above mentioned layers. Meanwhile, copper layer at the bottom of the RT
5880 substrate acts as a ground plane. Example of the complete 3-D geometrical dimension of a
triangular element is shown in Table 2.
3. RESULTS AND DISCUSSIONS
The study focuses on two main criteria, namely the static linear phase range and the bandwidth
obtained from the S-shaped curve of each element. Investigation on these parameters will determine
the best element which has the low loss performance and greater phase range to be selected as the
reflectarray element candidate. Figure 4(a) shows the reflection phase curve of the five different
elements that have been analyzed using the commercial full-wave electromagnetic software CST
Microwave Studio. The results show three resonant elements including ring, rectangular loop and
square loop have very close value of linear phase range. Referring to Figure 3, the linear phase
range can be calculated using Equation (1) below.
∆ϕ = ϕ1 − ϕ2
(1)
Table 3 summarizes the detail results of the static linear phase range as well as the reflection
loss values for each element. It can be observed that triangular loop element with reflection loss of
−1.2 dB offers a maximum static phase range of around 263◦ . Conversely, the elements of square
149
Reflection Phase (°)
Progress In Electromagnetics Research Symposium Proceedings, Taipei, March 25–28, 2013
f1
f2
Frequency (Hz)
Figure 3: Reflection phase versus frequency.
(a)
(b)
Figure 4: Comparison of simulated results among different reflectarray elements (a) reflection phase (◦ ) vs
frequency (GHz), (b) reflection loss (dB) vs frequency (GHz).
Table 3: Simulated linear phase range, reflection loss and bandwidth of different resonant elements.
Case
1
2
3
4
5
Element
Triangular
Ellipse
Ring
Rectangular
Square
Linear Phase Range (◦ )
262.815
197.114
165.044
162.329
153.449
Reflection Loss (dB)
−1.20
−0.65
−0.51
−0.53
−0.52
Bandwidth (%)
5.13
5.27
6.36
5.34
5.56
loop, ellipse loop, ring, and rectangular loop have linear phase range values less than 200◦ . The
square loop element with −0.5 dB reflection loss gives the minimum static linear phase range value
of about 153◦ . Meanwhile, it is observed that highest bandwidth value of 6.36% offered by ring
element at the lowest reflection loss. Conversely, the lowest bandwidth happened at triangular loop
element as it contributes the largest loss.
The simulated result in Figure 4(b) shows the triangular loop element has both the highest and
the lowest loss compared to the other shapes of element. It is happened because the triangular
element resonates at dual frequencies. At the resonant frequency of 14.09 GHz it has reflection
loss of −1.2 dB, while at the resonant frequency of 12.22 GHz the reflection loss is about −0.4 dB.
This is significantly due to the surface shape of the triangular loop element itself as shown in
Figure 5(e). One of the triangular loop element vertices has allowed higher current distribution in
that particular region which refers to the second resonant frequency. However, the other vertices
have low current distribution which results for the first resonant frequency. The red color in the
surface current density result generated by the CST computer model represents the region with the
higher current distribution.
Figure 5 shows the current distribution from the five different resonating elements. It can be
seen that triangular loop element has the maximum current density of 2128 A/m while the square
loop element has the lowest maximum current density of 444 A/m. These results occur due to the
fact that concentration of the current distribution depends on reflective area of each design element.
It is also noticed that, resonant frequency of each element straightly depends on the length, width
and diameter of the reflective area. As depicted in Table 4, triangular loop element has reflecting
PIERS Proceedings, Taipei, March 25–28, 2013
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(a)
(b)
(c)
(d)
(e)
Figure 5: Surface current density on reflectarray elements, (a) ellipse loop, (b) ring, (c) rectangular loop,
(d) square loop, (e) triangular loop.
Table 4: Surface current density and area of different element.
Case
1
2
3
4
5
Element
Triangular
Ellipse
Ring
Rectangular
Square
Surface Current (A/m)
2128
703
509
493
444
Area of Resonating Element (mm2 )
13.4
18.8
27.3
28.5
47.4
area of 13.4 mm2 thus it has the maximum surface current. Meanwhile, the square loop element
has reflecting area of 47.4 mm2 and this contributes to the lowest surface current value compared
to other elements. In conclusion, any modification made to the reflecting area of resonant element
will affect the surface current density.
4. CONCLUSIONS
Five different shapes of elements have been designed as a radiating element on a polycrystalline
silicon cell. The simulation results presented have shown that the elements phase performance
depends on size of the design area thus influence bandwidth. It also noted that shape of element
also contributes indirectly to the performance of resonant frequency. The results have shown that
triangular shape is the best candidate as the reflectarray antenna element as it offers the largest
linear phase range and the lowest reflection loss. Besides it also can operate at dual frequencies
within Ku-band.
ACKNOWLEDGMENT
The authors would like to thank the staff of Institute of Space Science (ANGKASA) of Universiti
Kebangsaan Malaysia for the technical support.
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