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APUSNCURSINRSM.2017.8072707

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A Wide-Band Dual-Polarized Reconfigurable SlotRing Antenna/Array with A Compact CPW Feeding
Structure
Junyi Huang, Mahmoud Shirazi, and Xun Gong
Department of Electrical & Computer Engineering
University of Central Florida, Orlando, FL 32816, USA
[email protected], [email protected]
Abstract—A wide-band dual-polarized reconfigurable slotring antenna/array using a compact CPW feeding structure is
presented. By using a CPW feeding mechanism, the mutual
coupling between the two orthogonal feeding lines is reduced
significantly compared to the traditional microstrip feeding
method while maintaining the antenna bandwidth. Furthermore,
the CPW feeding network is more compact than the microstrip
feeding network which is an important factor in large antenna
arrays.
Port 2
Port 1
Keywords—CPW feeding structure; dual polarized antenna;
reconfigurable antenna; slot-ring antenna; wide-band antenna;
I. INTRODUCTION
With significant advancements in modern wireless
communication systems, antennas with polarization diversity
and multi-functional capabilities are in increasing demand. A
multi-polarized antenna has the ability to increase
communication capacity and is suitable for mitigating fading in
a multipath propagation environment. On the other hand, dualband antennas with wide bandwidth in each mode of operation
can realize the functions of several independent antennas.
Therefore, a wide-band antenna with both dual-polarization and
dual-band capabilities will significantly advance the state of the
art. Slot antennas are an ideal choice for a dual-band, dualpolarized antenna because they have a planar feeding structure,
a wide bandwidth, high isolation, and can be extended to an
antenna array [1]. A compact dual-band, dual-polarized loopslot planar antenna was presented in [2]; a coplanar waveguide
(CPW) was used to excite the vertical polarization modes and a
microstrip line was used to excite the horizontal polarization
modes to obtain dual-polarized performance.
In [3], a wide-band singly-polarized reconfigurable slot-ring
antenna/array is presented. This antenna has several advantages:
a wide bandwidth in each operating mode, low power
consumption, and ease of fabrication. A dual-polarized slot
antenna was demonstrated in [4] that used a compact CPW
feeding method to use even and odd modes to excite two
orthogonal polarizations in a slot antenna, demonstrating
improved isolation between the two feeding lines.
In this paper, the same antenna aperture as described in [3]
is used to implement a dual-band, dual-polarized antenna with
reduced mutual coupling between the orthogonal feeding lines.
Other feed lines are
used for the C-band
operating mode
Two orthogonal feed
lines for the S-band
operating mode
Fig. 1. Schematic view of the wideband dual-polarized, dual-band slot-ring
antenna with microstrip feedlines.
S Parameter
0
-10
S11
S12
-20
4
5
6
7
8
Frequency(GHz)
Fig. 2. S-parameters of the wideband dual-polarized, dual-band slot-ring
antenna with microstrip feedlines
A compact CPW line is used to feed the wideband slot-ring
antenna array to obtain dual-polarization. By exploiting the even
and odd modes of the CPW line, the mutual coupling between
the two orthogonal feeding lines is decreased while the antenna
bandwidth is maintained.
The project is supported by the Defense Advanced Research Projects
Agency (DARPA) ACT Program under Grant HR0011-14-1-0003.
978-1-5386-3284-0/17/$31.00 ©2017 IEEE
1329
AP-S 2017
II. WIDE-BAND DUAL-POLARIZED RECONFIGURABLE SLOT-RING
ANTENNA/ARRAY
A. Traditional Microstrip Feeding Structure
A dual-polarized version of the same antenna aperture
described in [3] is illustrated in Fig. 1. Two operating modes are
defined for this antenna: the S-band and C-band operating
modes. The S-parameters of the antenna in the C-band operating
mode are shown in Fig. 2. It is seen that the return loss of port 1
is better than 10 dB from 5.3 GHz to above 8 GHz; however,
isolation between ports 1 and 2 is as low as 3.5 dB over the
frequency range. The horizontal polarization is not well isolated
from the vertical polarization, particularly in the C-band
operating mode, because the microstrip feed lines which feed the
antenna from the horizontal and vertical ports are physically
close to each other. Therefore, this antenna suffers from high
mutual coupling between two orthogonal feed lines and the
worst in-band mutual coupling is approximately 3.5 dB. In the
next section, a new feeding structure is applied to the antenna
array to mitigate the isolation problem.
B. Compact CPW Feeding Structure
Fig. 3 shows the geometry and dimensions of the compact
CPW feeding structure on the wide-band dual-polarized slotring antenna/array. A 50-Ω CPW feed line is used to excite the
2.66
1
6.65
4.3
Port 1
Port 2
Microstrip Feeding CPW Feeding
(a)
III. RESULT AND DISCUSSION
Fig. 4(a) depicts the return loss of ports 1 (microstrip feed
line) and 2 (CPW feed line) for the antenna in Fig. 3. When the
antenna is excited from port 1, ripples near 6.0 and 7.5 GHz are
observed in the return loss. Without considering these ripples,
the bandwidth of the antenna with the CPW feeding structure is
55% and 35% when excited from ports 1 and 2, respectively.
Compared to the bandwidth of the antenna with microstrip
feeding, the bandwidth is enhanced by 15% for the horizontal
polarization (the antenna is excited from port 1) and decreased
by 4% when the antenna is vertically polarized (the antenna is
excited from port 2).
Since the same antenna aperture as shown in Fig. 1 is now
fed with the compact CPW feeding structure, minor errors will
arise because the antenna geometry has been optimized to use
the microstrip feeding mechanism. If the antenna geometry is
optimized to use the new CPW feeding structure, better results
can be achieved. Fig. 4(b) demonstrates the mutual coupling
between port 1 and port 2 for the two feeding methods. The red
line shows the isolation between the two orthogonal ports of the
antenna with microstrip feed lines while the black line illustrates
the isolation between two orthogonal feed lines for the antenna
with the compact CPW feeding structure; it is seen that the
mutual coupling is improved by more than 7 dB from 4 to 6.5
GHz. The lowest isolation between ports 1 and 2 in the
microstrip design is 3.5 dB, while the worst isolation between
ports 1 and 2 using the CPW feeding structure is 8.5 dB,
demonstrating an improvement of 5 dB.
IV. CONCLUSION
(b)
A compact CPW feeding structure has been proposed to feed
a wide-band, dual-polarized slot-ring antenna/array to improve
isolation between two orthogonal ports and reduce the size of
the feeding network. A previously described microstrip feeding
method was compared with the proposed CPW feeding structure
on the same antenna aperture and it was shown that the compact
CPW feeding structure reduced the mutual coupling between the
two orthogonal feed lines by more than 5 dB without degrading
the bandwidth performance of the antenna.
Fig. 3. (a) The close-up view of the CPW compact feeding structure (b)
Schematic view of wideband dual-polarized antenna array with compact
CPW feeding structure (All dimensions are in mm).
0
0
S12 of New Feed
S12 of Former Feed
S Parameter
S11
S22
S Parameter
independent polarizations. When port 1 is excited, the CPW feed
line operates in the odd mode and the antenna is horizontally
polarized. Conversely, when port 2 is excited, the CPW feed line
is in its even mode and vertical polarization is observed. The
length and vertical position of the microstrip feed line and CPW
line are optimized to obtain a wide bandwidth.
-10
-10
REFERENCES
[1]
-20
4
5
6
Frequency(GHz)
(a)
7
8
-20
4
5
6
7
8
Frequency(GHz)
[2]
(b)
Fig. 4. (a) Return loss of port 1 and port 2 of the wideband dual-polarized
antenna array with CPW compact feeding structure (b) Mutual coupling
between two orthogonal feeding lines of new and former feeding structures.
[3]
vertical polarization while the orthogonal microstrip feed lines
on the back side of the antenna excite the horizontal polarization.
As with the previously described microstrip feeding mechanism,
the compact CPW feeding structure also supports two
[4]
1330
C. R. White and G. M. Rebeiz, "Single- and Dual-Polarized Tunable SlotRing Antennas," in IEEE Transactions on Antennas and Propagation, vol.
57, no. 1, pp. 19-26, Jan. 2009.
M. T. Tan and B. Z. Wang, "A Compact Dual-Band Dual-Polarized LoopSlot Planar Antenna," in IEEE Antennas and Wireless Propagation
Letters, vol. 14, no. , pp. 1742-1745, 2015.
M. Shirazi and X. Gong, "Singly-polarized reconfigurable slot-ring
antenna/array with fractal shapes," 2016 IEEE International Symposium
on Antennas and Propagation (APSURSI), Fajardo, 2016, pp. 843-844.
Yue Li, Zhijun Zhang, Wenhua Chen, Zhenghe Feng, Magdy F.Iskander,
“A Dual-Polarization Slot Antenna Using a Compact CPW Feeding
Structure,” IEEE Antennas and Wireless Propagation Letters , vol. 9, pp.
191–194, March 2010.
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