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High Gain, Wideband Grid Array Antenna for 28 GHz 5G Base Station

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This paper proposes a high gain grid array antenna (GAA) with enhanced bandwidth for 5G base station applications. The wideband GAA characteristics is achieved by loading the rhombus patch on the short radiating sides of the conventional GAA. By loading the rhombus on the short radiating sides of the conventional GAA, the additional capacitive reactance is introduced to cancel out the inductive reactance which leads to the enhancement on the bandwidth performance. The amplitude-tapering is applied to reduce the side-lobes levels of the grid array antenna. From the simulated results, it can be observed that the proposed GAA manages to support a −10 dB impedance bandwidth of 16.07% which is ranging from 27.5 GHz to 32 GHz with maximum achieved gain of 14.8 dBi. The overall dimension of the proposed wideband GAA is 25 × 25 × 0.787 mm 3 .
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High Gain, Wideband Grid Array Antenna for
28 GHz 5G Base Station
Wai Yan Yong1and Andr´
es Alay´
on Glazunov1,2
1University of Twente, Department of Electrical Engineering, Enschede, Netherlands, w.y.yongwaiyan@utwente.nl*
2Chalmers University of Technology, Department of Electrical Engineering, Gothenburg, Sweden.
Abstract—This paper proposes a high gain grid array antenna
(GAA) with enhanced bandwidth for 5G base station applications.
The wideband GAA characteristics is achieved by loading the
rhombus patch on the short radiating sides of the conventional
GAA. By loading the rhombus on the short radiating sides of
the conventional GAA, the additional capacitive reactance is
introduced to cancel out the inductive reactance which leads to
the enhancement on the bandwidth performance. The amplitude-
tapering is applied to reduce the side-lobes levels of the grid
array antenna. From the simulated results, it can be observed
that the proposed GAA manages to support a 10 dB impedance
bandwidth of 16.07% which is ranging from 27.5GHz to 32 GHz
with maximum achieved gain of 14.8dBi. The overall dimension
of the proposed wideband GAA is 25 ×25 ×0.787 mm3
.
Index Terms—Grid Array Antenna, millimeter wave, 5G, high
gain, amplitude tapering.
I. INTRODUCTION
The proliferation of new wireless applications such as the
Internet of things (IoTs), machine-to-machine (M2M) commu-
nication, E-health, E-business and E-learning result in increase
demands for much higher data rate communication services
[1]. In order to ensure the next generation wireless commu-
nication networks are capable to support this huge demand,
the millimetre wave (mmWave) band has been identified to
accommodate the new systems [2]–[4].
The mmWave band has been chosen to deliver high speed
services in 5G wireless networks. However, as compared
to the lower frequency band employed in the earlier gen-
eration telecommunication systems, the propagation pathloss
in mmWave is more significant [2]. To compensate for it,
advanced multiple antenna techniques have been proposed for
5G such as massive multiple-input multiple-output (MIMO)
and beamforming techniques [3], [5]. These techniques can
improve the gain of the antenna as well as provide a better
interference suppression capabilities. Given the huge number
of antenna elements that are needed, it is crucial to develop
a mmWave array antennas at a low cost, low complexity,
wideband performance, good integration capability and low
profile.
In order to achieve high gain performance at mmWave,
array antennas integrated with substrate integrated waveguide
(SIW) [6] and using multi-layer stacking technologies [7]
have been proposed. However, these techniques result in high
volume profile which result in the increase of fabrication
costs. In [8], frequency selective surface (FSS) design is
proposed to improve the antenna gain. However, when the
FSS is cascaded, the antenna bandwidth is dropped. Recently,
a grid array antenna has been proposed to realize a wideband,
high gain antenna for mmWave applications using multilayer
low temperature co-fired ceramic (LTCC) substrate [9], [10].
Although the LTCC technology manages to provide a good
performance, the fabrication process is complicated and incurs
in high fabrication costs. Therefore, the proposed solutions
become less practical for 5G base stations since a huge
number of base stations are expected to be built and a large
number of antennas will be employed. However, a practical
solution offering low profile features can be designed using
the conventional printed circuit board (PCB) technology [11].
Antennas of small-size, low-cost, high gain and wide fre-
quency band are desired for 5G base stations. This paper
presents a new broadband microstrip grid array antenna, which
is designed to be directly fed from a 50Ω coaxial line without
an impedance transformer. The wideband GAA is realized
by loading the rhombus into the short radiating sides of the
GAA. The broadband mmWave grid array antenna (GAA)
with low complexity and compact size is proposed for 5G
communication system without the need of using multilyaer
stacking or complicated LTCC technology.
II. WIDEBAND GRID ARRAY ANT EN NA DESIGN
The conventional GAA is composed of rectangular loops of
conductors above a ground plane with a single or multiple feed
point [12], [13]. The conventional GAA is designed to have
a long sides grid length of λgand short sides grid length of
λg
2, where λgis the guided wavelength [9], [12], [14].. Hence,
the long sides of the grid having an out-of-phase instantaneous
current distribution and short sides of the grid having in-phase
instantaneous current distribution. Although the conventional
GAA has been proven to have a good radiation performance,
the impedance bandwidth performance is still insufficient to
cover the entire proposed 5G frequency band that recom-
mended by Federal Communications Commission (FCC) as
the microstrip straight line radiating elements having a narrow
bandwidth in nature [15].
The proposed GAA is designed on the 0.787-mm-thick
Rogers RT 5880 substrate with dielectric constant of 2.2 and
loss tangent 0.0009. For bandwidth enhancement purpose, a
Fig. 1: Design of the proposed Wideband Grid Array Antenna
TABLE I: Optimized dimension of the proposed wideband
GAA
Parameters Lsub Wsub hWLLgSgLxg
Dimension(mm) 25 25 0.787 0.5 7.7 4.4 3.04
rhombus is added on the short sides of the grid as illustrated
in Fig. 1. By loading the rhombus on the short sides, the
capacitive reactance and the current path of the radiating
elements are increased. Hence resulting in the enhancement
of the GAA impedance bandwidth. To obtain the broadside
radiation pattern, the proposed GAA is fed with the 50
coaxial probe, located typically at the joint of the long and
short sides center elements of the antenna. The optimized
dimensions of the proposed wideband GAA are as tabulated
in Table I.
III. AMPLITUDE-TAP ER ED WIDEBAND GAA WITH
VARIABLE-SIZED RADIATIN G ELEMENTS
The amplitude-tapering (AT) technique is implemented on
the proposed wideband GAA for side-lobes level (SLL) re-
duction. The AT is performed in the manner where the
highest excitation is located at the centre area of the GAA.
The amplitude is reduced toward the radiating elements at
the edges of the GAA. Since the dimension of the short
radiating elements is controlling the impedance of the radiating
elements, where the smaller the size of the radiating elements,
the highest the impedance of the radiator and vice versa.
By implementing the AT in an aforementioned manner, the
radiating elements located at the centre row of the GAA are
carrying the maximum currents and vice versa. The proposed
AT wideband GAA is as illustrated in Fig. 2 and the optimized
dimension are tabulated in Table. II. To provide a better
understanding of the amplitude-tapering wideband GAA, the
corresponding current distribution of the proposed wideband
GAA before and after amplitude tapering is illustrated in Fig 3.
As it can be observed, when the AT is applied, the current
flowing on the sides radiating elements is decreased which
leads to the side lobes level reduction.
Fig. 2: Proposed Wideband Grid Array Antenna with AT
TABLE II: Optimized dimension of the proposed wideband
GAA
Parameters Lsub Wsub hLgSg
Dimension(mm) 25 25 0.787 7.8 4.6
Parameters Lxg WLd1d2d3
Dimension(mm) 3.11 0.5 1.7 2.7 3.77
Fig. 3: Current Distribution of the proposed wideband GAA
(a) Without AT and (b) With AT
Fig. 4: Comparison of the S11 with and without AT
Fig. 5: Comparison of the simulated gain and VSWR perfor-
mance of the proposed wideband GAA with and without AT
IV. RES ULTS AN D DISCUSSION
The proposed wideband GAA is modelled using the Com-
puter Simulation Technology (CST) software. Fig 4 shows
the comparison of the obtained S11 for the considered GAAs
with and without AT. It can be observed that the proposed
wideband GAA provides a 10 dB impedance bandwidth
of around 16.07% which is ranging from 27.5to 32 GHz.
The proposed GAA covers the entire 28 GHz frequency
band for 5G recommended by the Federal Communications
Commission (FCC) [16]. The simulated gain and VSWR per-
formance for the proposed wideband GAA with and without
AT is shown in Fig 5. The simulated GAAs show broadband
impedance matching with V SW R < 2.0and V SW R < 2.5
over the entire operational bandwidth for GAA without AT
and with AT, respectively. As can be seen from Fig 5, the
maximum achieved gain are approximately 14.3dBi and 14.8
dBi without and with AT, respectively. Hence, the impact of
the AT on the bandwidth and gain performance of the GAA
is negligible.
Fig. 6 shows the simulated radiation pattern of the proposed
antenna at 27.5GHz on the E- and H-planes in subplots (a) and
(b), respectively. Results are compared for designs with and
without the implementation of AT. Similar results are shown
in Figs. 7 and 8 for the 29 GHz and 32 GHz frequencies,
respectively. As can be observed from Fig. 6(a), the SLL of
the wideband GAA for the E-plane co-polar pattern is around
4dBi at 27.5GHz and enhanced to 11dBi with AT applied
on the wideband GAA. The enhancement of the SLL of the
E-plane co-polar radiation pattern for 29 GHz and 32 GHz
are more significant. At 29 GHz, the SLL from originally
5dBi and improved to 15dBi, with the improvement of
10dBi. As for 32 GHz, the SLL for E-plane radiation pattern
is 10dBi and 25dBi for wideband GAA without AT applied
and with AT applied, respectively. By implementing the AT on
the wideband GAA, it allows the higher current distributed
over the central elements and lower current distributed at
the radiating elements on the side. By having these current
distribution, it allows the increase in the gain of the main
(a)
(b)
Fig. 6: Comparison of the simulated co-polar radiation pattern
at 27.5 GHz with and without AT for (a) E-plane and (b)
H-plane
beam at the broadside direction and reduce the gain at the
SLL.
However, it is worthwhile to note that AT did not implied a
significant enhancement of the SLL for the H-plane co-polar
radiation pattern at 27.5GHz. This can be mainly attributed to
the improper control over the current phase alignment over the
GAA radiating elements. As it can be observed from Fig. 6(b),
the H-plane radiation pattern of the original rhombus loaded
wideband GAA at 27.5GHz, the main beam direction is
slightly tiled and with presence of grading lobes. As a result,
the implementation of the AT is ineffective on the H-plane
co-polar radiation performance at 27.5GHz. A similar trends
are observed for the at H-plane co-polar radiation pattern for
29GHz and 32GHz, where the AT does not give significant
enhancement on the grading lobes reduction. Besides that, the
insignificant effect of the AT can also be attributed to the
arrangement of the grid and the AT method implementation
illustrated in Fig. 2.
[h]
Table III shows a comparison of the performance of recent
developed planar mmWave array antennas. In [9], it has been
proposed to use the LTCC technology to enhance the band-
TABLE III: Performance comparison among the existing High Gain antenna for mmWave application where fcis the center
frequency and λois the wavelength of the center frequency
Ref. Antenna’s Types fc(GHz) Dimension Bandwidth (%) Peak Gain (dBi) Technique
[9] GAA 60 3λo×3λo×0.12λo15.6 17.7 LTCC
[8] Dielectric Patch 28 3λo×3λo×0.7λo15.54 17.78 Cascade FSS
[7] Linear Array 28 6.96λo×8.37λo×0.1λo6.3 21.4 Multilayer stacking
[6] Phased Array 28 6.54λo×5.93λo×0.21λo8.21 13.97 Multilayer substrate and
using SIW Feeding
[14] GAA 28 0.84λo×1.17λo×0.14λo13 7.3 PCB Substrate
This GAA 28 2.33λo×2.33λo×0.074λo16.07 14.8 PCB Substrate
Work
(a)
(b)
Fig. 7: Comparison of the simulated co-polar radiation pattern
at 29 GHz with and without AT for (a) E-plane and (b) H-plane
width performance of the conventional GAA with achievable
bandwidth of around 15.6%, while in [14] a thicker substrate
is proposed to get wider bandwidth of around 13% for the
conventional miniaturized GAA. In our paper, we manage to
achieve a wider bandwidth of 16.07% while keeping a low
volume profile. In addition, comparing to other high gain
antenna solutions which proposed FSS [8], multilayer stacking
[7] and SIW feeding [6], it is clear that the GAA manage to
provide a good gain performance at low profile. This make
GAAs a potential candidate for the 5G massive MIMO antenna
systems.
(a)
(b)
Fig. 8: Comparison of the simulated co-polar radiation pattern
at 32 GHz with and without AT for (a) E-plane and (b) H-plane
V. CONCLUSION
The bandwidth performance of the grid array antenna is
enhanced by loading the rhombus on the short radiating sides
of the conventional GAA. The amplitude tapering technique
has been applied to reduce the side-lobe levels of the proposed
wideband GAA. The dimensions of the proposed antenna are
25 ×25 ×0.787 mm3. The simulation results show that the
proposed wideband GAA having an impedance bandwidth
of 16.07% with a maximum gain of 14.8dBi. Comparing
the proposed design with other recently works using PCB
technology, the GAA has a high potential to be utilized as the
antenna element for 5G massive MIMO base station. It man-
ages to provide wideband and high gain performance while
keeping low-profile using the conventional PCB technology.
This work has opened up several questions that requires further
investigation. First, it is crucial to figure out a solution for
further SLL reduction for both E-plane and H-plane to get the
optimum radiation pattern. It is also important to eliminating
the grading lobes of the wideband GAA by properly control
over current phase synchronization of the GAA elements. We
will also develop a dual polarized wideband GAA for the
Massive MIMO base station.
ACKNOWLEDGMENT
This project has received funding from the European Unions
Horizon 2020 research and innovation programm under the
Marie Sklodowska-Curie grant agreement No. 766231 WAVE-
COMBE H2020-MSCA-ITN-2017. The authors would like to
thank Prof. Bing Zhang from Sichuan University, China for
his valuable discussion about the concept of the conventional
GAA.
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