Switchable Phased Antenna Array with Passive Elements for 5G Mobile
Terminals
Igor Syrytsin, Shuai Zhang and Gert Frolund Pedersen
Department of Electronic Systems, Aalborg University, Fredrik Bajers Vej, Aalborg, Denmark
Keywords:
Mobile Antenna, Phased Array, Reconfigurable Antenna, Passive Elements, Pattern Reconfigurability.
Abstract:
In this paper, a reconfigurable phased antenna array system is constructed for the mobile terminals in the
context of 5G communication system. The proposed antenna system operates at the resonance frequency of
28 GHz. The reconfigurability of the antenna element is achieved by using a passive slot antenna element
with a switch. The passive element acts as a reflector when the switch is turned off, and thus, change in the
main beam direction occurs. The antenna system consists of two sub-arrays on each of the short edges of
the ground plane. The coverage efficiency of over 70 % at 10 dBi threshold gain is achieved by the proposed
reconfigurable phased antenna array.
1 INTRODUCTION
In the recent years the research towards the 5th gen-
eration communication systems has been a hot topic.
Additionally, the bandwidth is a scarce resource at the
frequency bands between 700 and 3500 MHz. Thus,
in (Rappaport et al., 2013) it has been proposed to use
frequency bands in cm/mm-wave range. To counter-
act the high path loss experienced at the cm and mm-
wave frequencies, the beamforming option at both
mobile and base stations has been considered in (Roh
et al., 2014).
Phased arrays for the cm-wave frequencies has al-
ready been introduced (Hong et al., 2014), (Helander
et al., 2016), and (Zhao et al., 2016). In (Hong et al.,
2014) it has been proven that an efficient phased an-
tenna array can be realized on the typical mobile de-
vice form factor. The coverage efficiency metric has
been introduced in (Helander et al., 2016). Later on,
in (Zhao et al., 2016) the effect of the user’s body
on mobile phased array performance has been stud-
ied using the coverage efficiency metric. Finally in
(Zhang et al., 2017) the 3D-coverage of a switchable
phased array design has been proposed. In the de-
sign, the surface wave has been efficiently excited in
order to achieve pattern diversity of sub-arrays. How-
ever, the complexity of the proposed system is rather
high. A total of 3 sub-arrays of 8 elements each has
been utilized in (Zhang et al., 2017). In this paper, a
phased antenna array design, based on the pattern re-
configurable antenna element has been proposed. The
main aim of the paper is to show how to obtain higher
coverage efficiency and at the same time reduce the
complexity of the phased antenna array system, by
using a pattern reconfigurable array element. In the
proposed antenna system multiple passive elements
are introduced in order to change the main beam di-
rection of the radiation pattern. Antennas based on
the similar principle has been introduced in (Zhang
et al., 2004), where the length of the two parasitic el-
ements have been changed by using switches. The
idea proposed by (Zhang et al., 2004) has been ex-
panded in designs of Yagi patch antenna in (Yang
et al., 2007), planar circular UWB monopole antenna
in (Aboufoul et al., 2013), and a dipole with director
and reflector elements in (Trad et al., 2013). How-
ever, a mobile phased antenna array based on pat-
tern reconfigurable elements has not been designed
yet. In this paper, the operation and geometry of the
proposed pattern reconfigurable antenna element will
be described. Then, the radiation properties of the
mobile antenna array composed of the reconfigurable
antenna elements will be verified. Finally some inter-
esting conclusions will be drawn.
2 ELEMENT GEOMETRY AND
PRINCIPLE OF OPERATION
In this section the geometry and principle of opera-
tion of the proposed reconfigurable antenna element
62
Syrytsin, I., Zhang, S. and Pedersen, G.
Switchable Phased Antenna Array with Passive Elements for 5G Mobile Terminals.
DOI: 10.5220/0006394500620066
In Proceedings of the 14th International Joint Conference on e-Business and Telecommunications (ICETE 2017) - Volume 6: WINSYS, pages 62-66
ISBN: 978-989-758-261-5
Copyright © 2017 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
will be explained. The performance on the proposed
antenna array has been investigated by simulating in
CST Microwave Studio using the FDTD solver with
accuracy of −50 dB and 2.6 million mesh cells.
The geometry of the proposed reconfigurable pla-
nar antenna element is shown in Figure 1. The an-
tenna consists of a driven element and a passive ele-
ment. A driven element has characteristics of a slot
antenna. The slot has been formed by the ground
plane and a strip, connected by two vias, as shown
in Figure 1(c). A passive parasitic slot element with
a switch in the middle in Figure 1(a) has been placed
3 mm from the edge of the ground plane. The driven
element is feeded between the edge of the ground
plane and a strip on the other side of the ground plane
as shown in Figure 1(c). The antenna has been printed
on the PCB made of the Nelco N9000 substrate with
ε
r
= 2.2 and a loss tangent of 0.0009.
The current distributions of the reconfigurable an-
tenna are shown in Figure 2. A passive element can
have two states: the ON state, when the switch acts as
(a)
(b)
(c)
Figure 1: Geometry of the proposed switcheble antenna ar-
ray system in (a) front, (b) back, and (c) side views.
a short and the OFF state where the switch acts as an
open. From the back view, the surface current distri-
butions look similar for the both states of the switch
in Figure 2(a) and Figure 2(b) . However, from the
front view in Figure 2(c) it can clearly be seen that
the driven element couples to the passive slot element
when the switch is in OFF state. When the switch is in
OFF state, the passive element acts as a reflector. On
the other hand, when switch is in ON state, the current
flowing on the passive slot element in Figure 2(d) is
very weak. When switch is in ON state, the electri-
cal length of the slot is reduced and thus there is no
impact on the radiation pattern of the driven element.
The coupling between passive and driven ele-
ments will change matching of the driven element.
The change in the reflection coefficient due to cou-
pling to the passive element is illustrated in Figure 3.
The resonant frequency is moved by 400 MHz to the
lower frequencies when the switch is in ON state.
Nonetheless, over 1 GHz of the -6 dB bandwidth can
be achieved.
(a) (b)
(c) (d)
Figure 2: Surface currents of the proposed antenna element
(a) back view switch is OFF, (b) back view switch is
ON, (c) front view switch is OFF, and (d) front view
switch is ON.
Figure 3: Resonant frequency displacement because of the
reflector coupling.
The proposed antenna element location on the typ-
ical chassis of the modern mobile terminal and a co-
ordinate system used in the simulations are shown in
Figure 4.
Switchable Phased Antenna Array with Passive Elements for 5G Mobile Terminals
63
Figure 4: Antenna location and coordinate axis.
The radiation patterns polar plots for the two states
of the switch are shown in Figure 5 for the constant
φ = 90
. The main beam direction has been suc-
cessfully changed from θ = 110
in Figure 5(a) to
θ = 45
in Figure 5(b). A Maximum gain of 4.5 dBi
and 5.78 dBi has been acquired for the switch in OFF
and ON states respectively.
(a) (b)
Figure 5: Realized gain of the antenna element with the
switch in (a) OFF state, and (b) ON state.
3 ANTENNA ARRAY
PERFORMANCE
In this section the performance of the proposed recon-
figurable phased antenna array will be verified. All of
the simulations has been done by using FDTD solver
in CST Microwave Studio with an accuracy of −50 dB
and 3.9 million mesh cells.
The proposed antenna element has been combined
into an array of 9 elements(9 driven and 9 passive el-
ements). Additionally, two of such sub-arrays have
been placed on the ground plane’s edges in order to
form the reconfigurable antenna system. The geom-
etry of the mobile phased antenna array is shown in
Figure 6. It can clearly be seen that the antenna ar-
ray is low profile and very small in comparison to
the ground plane. No clearance is required in the ge-
ometry of the proposed antenna array, however, some
space on the ground plane is required for the passive
slots and metal strips. The ground plane of 65 mm ×
125mm has been chosen to illustrate the array perfor-
mance on the form factor of the typical mobile ter-
minal. The spacing between elements has been set
to 7 mm, which corresponds to 0.7λ @28 GHz. The
reconfigurable phased antenna array can be scanned
when switches on passive elements are in ON or OFF
states. Thus, only two feeding networks are required
in an application.
Figure 6: Geometry of the proposed antenna array shown in
(a) front view, and (b) back view.
The total scan pattern of the proposed reconfig-
urable phased antenna array is shown in Figure 7(a).
A total scan pattern of the phased array is obtained
when the phased array is scanned for all the avail-
able phase shifts. This procedure has been repeated
for both sub-arrays. The maximum scan angle of the
phased array has been defined in this paper as the
point where a main lobe of the array is of the similar
power as the greeting lobe. Four main lobes can be
obtained by changing the state of switches on the pas-
sive elements and switching between two sub-arrays
as shown in Figure 7(a).
The coverage efficiency is calculated from the to-
WINSYS 2017 - 14th International Conference on Wireless Networks and Mobile Systems
64
tal scan pattern. Coverage efficiency has been defined
by (Helander et al., 2016) as:
η
c
=
Coverage Solid Angle
Maximum Solid Angle
(1)
The coverage efficiency, calculated from the total
scan pattern, is displayed in Figure 7(b). The value
of coverage efficiency at 10 dBi is of interest because
the high antenna gains will be required in 5G mobile
communication systems in order to make robust link
budgets. Especially, when the user is located far away
from base station, substantial antenna gains are re-
quired in order to compensate for the high path loss.
In Figure 7(b) a coverage of 0.7 (70 %) can be ob-
tained by the proposed reconfigurable antenna array
at the threshold gain of 10 dBi. The coverage perfor-
mance of the proposed reconfigurable phased array is
higher than a phased array described by (Zhao et al.,
2016) and (Helander et al., 2016), but however, com-
plexity is higher. Moreover, coverage of the proposed
reconfigurable phased antenna array at 10 dBi gain is
20 % higher than of switchable antenna array system
constructed by (Zhang et al., 2017). Not to mention,
complexity is reduced by using two sub-arrays instead
of three. In application one less sub-array means in-
crease in the overall performance of the system be-
cause less lossy phase shifters are required.
(a)
(b)
Figure 7: Plots of (a) total scan pattern of the proposed
phased antenna array, and (b) coverage efficiency.
4 CONCLUSION
In this paper, multiple passive slot array elements
have been used in order to increase the coverage of the
linear uniform mobile phased antenna array. Further-
more, two sub-arrays of 9 elements each have been
placed on each of the short sides of the ground plane.
The antenna system operates by twitching between
the two phased sub-arrays. Each phased array can be
scanned when the corresponding passive elements are
switched on or off. The passive elements are included
in the design in order to change the main beam di-
rection of a chosen sub-array. Coverage efficiency of
the proposed reconfigurable antenna array system is
over 70 % at 10 dBi threshold gain, which is higher
than a current state of the art mobile phased antenna
arrays. Finally, the prototype of the proposed antenna
has been constructed and measured in an an-echoic
chamber. The measured radiation patterns for both
switch states follow the simulations.
5 MEASUREMENTS
In this section the antenna prototype and measure-
ments are presented. It has been chosen to only mea-
sure a single antenna, because of the lack of phase
shifters or Rotman lens. The geometry of the pro-
posed switchable phased antenna array prototype is
shown in Figure 8. The Figure 8(a) shows the back
view of the antenna. The Figure 8(b) displays the
front view of the antenna, where a coaxial cable with
SMA connector has been added to make antenna feed-
ing. In Figure 8(c) an antenna feeding and vias have
been displayed in detail.
(a) (b)
(c)
Figure 8: Geometry of an antenna prototype in (a) back
view, (b) front view, and (c) side view.
In order to measure the radiation pattern of the an-
tenna, the antenna has been placed on the positioner in
Switchable Phased Antenna Array with Passive Elements for 5G Mobile Terminals
65
an an-echoic chamber in Figure 9(a). The correspond-
ing coordinate system of the measurement setup has
also been explained in Figure 9(b). It has been cho-
sen to represent the switch on the passive slot with the
wire, which can be soldered on or off. Furthermore,
the reflection coefficient of the antenna has also been
measured and shown in Figure 9(b). The resonant fre-
quency has been shifted noticeably towards the lower
frequencies because of the mock-up production inac-
curacies.
(a) (b)
Figure 9: Measurement setup in the an-echoic chamber (a),
and measured reflection coefficient (b) of the prototype an-
tenna.
The resulting measured and simulated radiation
patterns for the both states of the switch is shown in
Figure 10. It can be noticed that measured radiation
patterns are more noisy because of the added cables.
In order to compare the simulations to measurements
it has been chosen to look on the main beam direc-
tions. In Figure 10(a) and Figure 10(b) the strong
beam at φ = 220
can be observed. In Figure 10(c)
and Figure 10(d) the beams at φ = 180
,φ = 0
, and
φ = 360
are observed.
(a) (b)
(c) (d)
Figure 10: Radiation pattern of the (a) simulated antenna
switch is on, (b) measured antenna switch is on, (c)
simulated antenna switch is off, and (d) measured antenna
– switch is off.
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