Broadband Resonant Elements for 5G Reflectarray Antenna Design

TELKOMNIKA, Vol.15, No.2, June 2017, pp. 793~798
ISSN: 1693-6930, accredited A by DIKTI, Decree No: 58/DIKTI/Kep/2013
DOI: 10.12928/TELKOMNIKA.v15i2.6122  793
Received January 7, 2017; Revised March 28, 2017; Accepted April 11, 2017
Broadband Resonant Elements for 5G Reflectarray
Antenna Design
M. Hashim Dahri*
1
, M. R. Kamarudin
2
, M. H. Jamaluddin
3
, M. Inam
4
, R. Selvaraju
5
Wireless Communication Centre, Faculty of Electrical Engineering, Universiti Teknologi
Malaysia, 81310 Johor Bahru, Malaysia
Corresponding author, e-mail: muhammadhashimdahri@yahoo.com*
1
, ramlee@fke.utm.my
2
,
haizal@fke.utm.my
3
, inam-pd@utm.my
4
, sraghuraman2@live.utm.my
5
Abstract
The performance investigation of two novel resonant elements is presented in this work
for 5G reflectarray antenna design. Two dual resonance elements with wide reflection phase
range have been developed from a square patch element by a novel corner bending tactic. The
reflection loss and reflection phase range performance of the proposed elements have been
compared with conventional square patch element at 26 GHz. The results have shown a
reflection phase swing of 629° and 632° for Bent Width and Bent Length elements respectively.
The broadband features of proposed elements can radically improve the bandwidth
performance of a reflectarray antenna.
Keywords: Reflection loss, Reflection phase, Progressive phase distribution, Surface currents,
Dual resonance
Copyright © 2017 Universitas Ahmad Dahlan. All rights reserved.
1. Introduction
Reflectarray antenna consists of an array of printed microstrip patches on a flat
grounded dielectric substrate illuminated by a feed horn. It is a light weighted, flat and low profile
antenna with beam scanning capabilities [1, 2]. It combines the best features of parabolic and
phased array antennas with least possible drawbacks. Patch element which contributes as a
unit cell of reflectarray plays an important role for its design realization with optimized
characteristics [3-5]. The unit cell patch element is designed to reflect the incident signals
coming from the feed horn into a desired direction with a planar wave front, as shown in Figure
1. The planar wave front is required to achieve high gain with pointed beam characteristics [2].
Here comes the drawback of the reflectarray antenna which restricts it to attain a planar wave
front. It is the narrow bandwidth of its unit cell element with reflection phase errors [6]. The
inability of unit cell element to acquire a full 360° reflection phase swing is the main reason
behind the generation of differential spatial phase delays in the reflected signals. These variable
time delays in reflected signals create non planar wave front and restrict them to attain high
gain. The effect of phase errors is even more challenging to control at higher frequencies such
as millimeter waves due to shorter wavelengths [7]. Subsequently the future fast communication
systems such as 5G are proposed to work at the higher frequencies due to their high data rate
requirements [8, 9]. High data rates require fast switching mechanism [10] which is only
possible to attain at short wavelengths with high frequencies.
Therefore in this work, a novel design aspect of a square patch reflectarray antenna has
been proposed for wide bandwidth operation at K-band frequency range. The proposed
technique is used to form two different patch elements with broadband features at 26 GHz for
5G operation. Simulations of proposed designs have been performed by CST computer model
with proper boundary conditions applied for infinite array approach. Reflection loss, surface
currents and reflection phase range of proposed elements have been studied in details to
comply them with the requirements of 5G communication systems.

 ISSN: 1693-6930
TELKOMNIKA Vol. 15, No. 2, June 2017 : 793 – 798
794
Figure 1. Reflectarray antenna operation principle
2. Design Considerations
Different frequency bands have recently been suggested for 5G communications based
on their capabilities to attain required features [11]. In this work, the frequency band from 24.25
GHz to 27.5 GHz has been selected for design considerations. A resonant frequency of 26 GHz
has been chosen for the designing of unit cell reflectarray. This band of frequency provides
wider wavelengths compared to other proposed bands which is required particularly for less
design complexity.
Figure 2. Schematics of proposed broadband elements along with a square patch element
The conventional square patch element of reflectarray antenna has been taken as a
reference to propose two different broadband elements with a novel configuration. Figure 2
depicts the designs and the process of development of the proposed elements. It can be seen
from Figure 2 that, the proposed novel elements have been created by bending one corner of
the reference element. A bend in width at the top right corner produces Bent Width element with
two different combinations of lengths and widths. Similarly, a bend in length at the same corner
produces Bent Length element with a different combination of lengths and widths. The reference
square patch element has same dimensions for length and width which produce a single
resonant frequency. On the other hand, two different combinations of lengths and widths as in
proposed designs tend to modify the E-Fields and flow of the surface currents. This modification
generates two closely spaced resonant frequencies for proposed unit cell elements with
broadband features. Rogers 5880 substrate with a thickness of 0.256 mm has been selected to
hold the mentioned patch elements due to its optimum loss performance.
3. Results and Discussions
The element designs discussed in previous section have been simulated using
commercially available computer model of CST MWS and results have been analyzed for
performance investigation. As aforementioned, the bending tactic was only performed on the top
right corner of the square element. The effect of the same bending on any other corner of the
square element can also be the same. The reason behind this is that the bending at any other

TELKOMNIKA ISSN: 1693-6930 
Broadband Resonant Elements for 5G Reflectarray Antenna Design (M. Hashim Dahri)
795
corner can also create electrically identical shapes of the patch element as compared to
proposed broadband elements. In this section the effect of the bending on the generation of the
second resonance with extended reflection phase range is thoroughly studied. Then the results
of proposed novel elements with optimized bending value are compared with the square patch
element. Finally the progressive phase distribution performance of proposed broadband
elements as a function of their variable size is presented.
3.1. Development of Broadband Novel Elements
The bending depth “d” as shown in Figure 2 for Bent Width and Bent Length elements
has been varied gradually in order to observe the effect of the generation of a second
resonance. The occurrence of a second resonance for Bent Width element starts when “d”
value reaches at 0.15 mm as shown in Figure 3. It has been observed from Figure 3(a) that, as
the bending depth varied from 0.15 mm to 0.5 mm the separation between the two resonances
increases. Moreover, the reflection loss of second resonance also gradually decreases from
14.35 dB to 4.17 dB with increasing “d”. The generation of second resonance can also create an
extra reflection phase swing as can be seen from Figure 3(b) where more than 600° of reflection
phase swing has been observed.
(a) (b)
Figure 3. Effect of variable bending depth on the performance of Bent Width element
(a) reflection loss (b) reflection phase
(a) (b)
Figure 4. Effect of variable bending depth on the performance of Bent Length
element (a) reflection loss (b) reflection phase
Figure 4 depicts the performance of Bent Length element with respect to a variable
bending depth “d” in length of the element. It can be observed from Figure 4(a) that, the second
resonance starts to generate from bending depth of 0.16 mm. As the “d” increases from 0.16
mm to 1 mm the reflection loss of the second resonance decreases from 14.21 dB to 4.15 dB.

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796
Moreover, the separation between the two resonances is smaller as compared to Bent Width
element. It shows that, the performance of Bent Length element is less sensitive to the bending
depth as compared to Bent Width Element. Similarly, Figure 4 (b) depicts a full reflection phase
swing of more than 600° due the generation of two resonances in Bent Length element. The
occurrence of two resonances in both proposed elements is due to the difference in their L1 and
L2 values, as depicted in Figure 2. For Bent Width element the length L1 is less than L2 which
generates a second resonance at a higher frequency.
Alternatively, a second resonance at a lower frequency for Bent Length element is due
to a longer L1 compared to its L2. Similarly two different widths of proposed broadband
elements are responsible for the change in reflection loss performance of their second
resonances. As the difference between W1 and W2 of proposed elements increases their
reflection loss gradually decreases.
3.2. Optimized Performance of Broadband Novel Elements
The bending depths of proposed broadband elements have been kept constant at
prescribed values in order to find an optimized performance as compared to a conventional
square patch element. The bending depths have been set at 0.35 mm and 0.2 mm for Bent
Width and Bent Length elements respectively. The performance comparison of proposed
broadband elements with a square patch element has been depicted in Figure 5. It can be
clearly observed from Figure 5 that, the reflection loss performance of both broadband elements
at their first resonances is almost similar to that of square patch element. Alternatively, the
reflection phase range performance of both proposed elements is considerably better than that
of square patch element. Table 1 summarizes the comparison of square patch element with
proposed novel elements.
(a) (b)
Figure 5. Performance comparison of proposed broadband elements with square patch
element (a) Bent Width element (b) Bent Length element
Table 1 describes that, proposed elements possess two resonances as compared to a
single resonance of square patch element. Reflection loss performance of Bent Width element
at 26.84 GHz is greater than that of at 25.5 GHz. This is because of a higher concentration of
surface currents at 26.84 GHz as compared to at 25.5 GHz. The similar trend can also be seen
for Bent Length element. Moreover, Bent Width and Bent Length elements attain a full reflection
phase swing of 629° and 632° respectively, as compared to a 273° of square patch element.
This is because of a higher surface current distribution of 2221 A/m and 2429 A/m for Bent
Width and Bent Length elements respectively, as compared to a 932 A/m of square patch
element.

TELKOMNIKA ISSN: 1693-6930 
Broadband Resonant Elements for 5G Reflectarray Antenna Design (M. Hashim Dahri)
797
Table 1. Summary of performance parameters of square patch, Bent Width and Bent Length
elements
Parameter Square Element Bent Width element Bent Length element
Resonant Frequency (GHz) 26 25.5 26.84 25.288 26
Reflection Loss (dB) 0.687 0.86 5.06 10.1 0.787
Max. Surface Currents (A/m) 932 1141 2221 2429 767
Full Phase Swing (°) 273 629 632
3.3. Progressive Phase Distribution
A full reflectarray antenna is made of a number of reflecting elements with a proper
reflection phase distribution in order to reflect the signals with planar wave front. It is called
progressive phase distribution of the elements which can be attained by varying the size of the
elements [1]. Figure 6 shows the progressive phase distribution of proposed broadband
elements with respect to their varying length “L1” at 26 GHz. The overall size of the proposed
elements has been varied with same margins as of their length “L1”. However their bending
depth values have been kept constant. As shown in Figure 6(a), Bent Width element acquired a
progressive phase distribution of 575° when its length is changed from 3.55 mm to 3.77 mm.
Similarly for Bent Length element a change in length from 3.63 mm to 3.79 mm attained a
progressive phase distribution of 530°. This phenomenon also shows that, the reflection phase
of Bent Width element is more sensitive to its dimensions as compared to Bent Length element.
Additionally, the extended progressive phase distribution of proposed elements verifies their
broadband features.
(a) (b)
Figure 6. Progressive phase distribution of proposed broadband elements at 26 GHz (a) Bent
Width element (b) Bent Length element
4. Conclusion
The detailed analysis of development of broadband elements from a conventional
square patch element has been provided. It has been shown that, broadband features can be
attained by bending one corner of the square patch element. The effect of bending depth on the
performance of proposed broadband elements has been thoroughly analyzed. Two different
resonances can be achieved from a single element by applying the proposed technique. The
generation of second resonance is solely responsible for the extension of reflection phase swing
beyond 600°. The verification of results by testing will be performed in near future. The simple
designs of proposed broadband elements can provide ease of fabrication at high frequencies for
5G communication. Moreover, their broadband performance can also be utilized to develop a
5G reflectarray antenna.
Acknowledgements
This project is sponsored by the Ministry of Education Malaysia, Ministry of Science
Technology and Innovation (MOSTI) and Universiti Teknologi Malaysia under Vot 4J211, Vot
03G33 and Vot 4S134.

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798
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