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

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

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

= 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)

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

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

tal scan pattern. Coverage efﬁciency has been deﬁned

by (Helander et al., 2016) as:

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

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)

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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WINSYS 2017 - 14th International Conference on Wireless Networks and Mobile Systems