Appl. Phys.

A (2017) 123:48
DOI 10.1007/s00339-016-0694-3

Flexible ultra-wideband antenna incorporated with metamaterial

structures: multiple notches for chipless RFID application
M. E. Jalil1 • M. K. A. Rahim1 • N. A. Samsuri1 • R. Dewan1 • K. Kamardin2

Received: 16 August 2016 / Accepted: 12 December 2016

 Springer-Verlag Berlin Heidelberg 2016

Abstract A coplanar waveguide (CPW) ultra-wideband 1 Introduction

(UWB) antenna incorporated with metamaterial—split ring
resonator structure—that operates from 3.0 to 12.0 GHz is Barcode technology is an optical machine-readable data
proposed for chipless RFID tag. The 30 mm 9 40 mm system. The data are represented by capturing the image
flexible chipless RFID tag is designed on the fleece sub- code for identification activity such as for the purchasable
strate (er = 1.35, thickness = 1 mm and tan d = 0.025). products at the supermarket and asset tracking management
A six-slotted modified complementary split ring resonator commonly located at the store room. However, the limi-
(MCSRR) is introduced into the ultra-wideband antenna to tations of barcode are the reading range, existence of image
produce multiple band notches at 3.0, 4.0, 5.0, 6.0 and obstacle and the orientation sensitivity. Therefore, the radio
7.0 GHz. The frequency shifting technique is introduced frequency (RF) barcode is introduced to replace the con-
for designing a high-capacity chipless RFID tag with ventional barcode which potentially can provide better
compact size. Each MCSRR is able to code in four dif- performance. The chipless RFID barcode is designed and
ferent allocations (00, 01, 10 and 11). To achieve encoding this technique has been growing since the discovery of
of 10-bits data (10,234 number), six MCSRRs are proposed improvement technique for RFID performance.
with three-slotted MCSRR in the radiator and three-slotted Low cost, flexible and light weight are the main criteria
MCSRR in the ground plane. in designing chipless RFID barcode to reduce the fabrica-
tion cost, enhance mobility and provide comfort to the user.
The RF barcode textile based such as fleece, flannel and
& M. K. A. Rahim
denim are recommended for body centric communication
mdkamal@utm.my especially in wearable application. Furthermore, the textile
M. E. Jalil
material is ergonomically and easily conformable to any
ezwanjalil@gmail.com surface [1, 2].
N. A. Samsuri
One of the challenges in designing chipless RFID bar-
asmawati@utm.my code is the high capacity and compact in size. To solve the
R. Dewan
problem, metamaterial structure is proposed which offers
raimidewan@gmail.com numerous potential benefits such as performance
K. Kamardin
enhancement, size miniaturization and multiple frequencies
kamilia@utm.my capability. Metamaterials have been widely used in
designing filters, antennas and absorbers design with
1
Advanced Radio Frequency and Microwave Research Group miniaturization, multiple frequencies and narrow band-
Communication Engineering Department, Faculty of
width benefits [3–5]. In microwave, the metamaterial
Electrical Engineering, Universiti Technologi Malaysia,
81310 Johor Bahru, Johor, Malaysia structure is able to change the permittivity and permeability
2 of a design, either in positive or negative by altering the LC
Computer Systems Engineering Group, Advanced
Informatics School, Universiti Teknologi Malaysia (UTM), design circuit. Split ring resonator is one of the metama-
54100 Kuala Lumpur, Malaysia terial structures that offer high Q factor and is suitable to

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48 Page 2 of 5 M. E. Jalil et al.

produce high band notch. The existence of band notch is to In this paper, the CPW UWB antenna with integrated
enhance the data of RF barcode by maximizing the number slotted modified complementary split ring resonator
of resonators in specific frequency range. (MCSRR) which acts as the encoding element is proposed
to minimize the passive tag size by changing the multiple
1.1 Chipless RFID concept resonators method to the band-notches method. The
antenna design has the capability to produce 10 bits chip-
The block diagram of the proposed RF barcode consists of less RFID with each of the frequency range dependent with
RFID reader and chipless RFID tag is as shown in Fig. 1. the resonating bit and is suitable for the far-field commu-
The concept of chipless RFID system is similar with the nication application. Typically, band notch characteristic is
conventional RFID system. Basically, the RFID reader will widely used for the rejection of unwanted interference of
transmit interrogated signal with a particular magnitude specific frequency band [10].
and phase data to the RF barcode. Then, the chipless tag
with band notch structure encodes the interrogation signal 1.2 Design consideration
into various frequency spectrums in terms of magnitude
and phase and retransmitted back the signal to the reader Figure 2 shows the UWB antenna with multiple split ring
[6]. structure. Three different designs have been implemented
From previous research, Predavovic et al. [7] has started without and with modified complementary split ring res-
to design a passive chipless with 35-bits capacity using two onator (MCSRR).
different polarizations of ultra-wideband (UWB) antenna The proposed design is simulated by using Computer
with separation of 35 number of spiral resonator from 3.1 Simulation Technology (CST) Microwave Studio 2015.
to 7 GHz (UWB frequency range) with dimension of The MCSRR is introduced into the antenna structure to add
88 mm 9 66 mm. Cheung et al. [8] has proposed the 8-bits multiple bands notch by properly adjusting the ring cur-
of chipless RFID which combine two CPW UWB antennas vature and gap. The UWB antenna only (A1), the mono-
and coplanar waveguide resonator using only one side of pole with integrated three-slotted MCSRR at the radiator
the radiating element. Previously, an 8 bits passive chipless (A2) and monopole with integrated three-slotted MCSRR
RFID has been designed using MCSRR structure and at the radiator and (A3) the double two-slotted MCSRR at
transmission line with dimension of 25 mm 9 50 mm for the backside are designed.
near-field communication [9].
All the mentioned types of chipless RFID are based on
the retransmission of passive tag method [7–9]. The tech-
nique sends information signal back to the reader antenna
which involves other antenna as a radiator and multiple
resonator as a data encoder, located in the transmission
line. One way to reduce the chipless RFID size is to con-
vert multiple resonators in the transmission line to the
slotted notch antenna. Therefore, the size of the transmis-
sion line can be minimized with the absence of multiple
resonators.

Fig. 2 Proposed UWB antenna; a first design (A1), second design

Fig. 1 Block diagram of RF barcode [6] (A2), third design (A3) and S11 of the proposed antennas

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Flexible ultra-wideband antenna incorporated with metamaterial structures: multiple notches… Page 3 of 5 48

The S11 performance of the proposed antenna is com-

pared with the reference antenna; a slotted stub based on
previous research [11] in Fig. 3. The reference antenna
consists of a shovel-shaped radiating patch with five
C-shaped slotted structure. Based on Fig. 3, the proposed
slotted MCSR antenna provides narrow notch band com-
pared to the reference antenna. This characteristic allows
the maximization of data capacity using frequency shifting
technique. At the same time, the proposed antenna provides
stable notches frequencies at all peak frequencies without
affecting the adjacent notches due to distance maximizing
between the slots. The slot length of the proposed antenna
is shorter compared with the conventional structure due to
metamaterial behavior.
All antennas have been designed on fleece substrate with
Fig. 4 Illustration of frequency shifting technique for data encoding
relative permittivity of 1.25, loss tangent of 0.0025 (at
2 GHz) and thickness of 1 mm. A 50 X connector is
connected on the upper part of the substrate to excite the
antenna with feed width of 4 mm to obtain suit-
able impedance matching. To implement the three band
notches characteristics for the antenna A2, the three rings
slotted with curvature of 34.95 mm at 4.0 GHz, 23.10 mm
at 6.0 GHz and 16.89 mm at 8.0 GHz are symmetrically
arranged at the center of the radiator. The finalized antenna
has frequency band notches at 4.0, 5.0, 6.0, 7.0 and
8.0 GHz with the addition of slotted rings with curvature of
27.44 and 19.28 mm.
Fig. 5 S11 plot of antenna with different gap of outer ring
1.3 Results and discussion
From previous research, a single ring resonator that
The frequency shifting approach as shown in Fig. 4 is encodes only a single bit has been reported in [7]. How-
introduced to improve the amount of bits generated by a ever, the frequency shifting approach as shown in Fig. 4 is
single-slotted ring resonator. For data encoding, each introduced to improve the number of bits generated by a
notch represents three bits with nine different frequencies single resonator. The length of slot resonator has inverse
conditions. For example, the first notch ring resonator will relationship with resonant frequency. The addition of gap
encode bits 00, 01 and 10 depending on the maximum size reduces the length of resonator and increases the res-
notch frequency, (00 = 4, 01 = 4.2 and 10 = 4.4 GHz) onant frequency.
by varying the gap between the first outer ring at the For example, by varying the gap between the slotted
patch. outer ring of patch from 2.0, 2.5, 3.0 and 3.5 mm, bits of
00, 01, 10 and 11 are encoded. The relation between gap
and resonant frequency is shown in Fig. 5. The gap of 2.0,
2.5, 3.0 and 3.5 mm resonates at four different resonant
frequencies which are 4.1 (00), 4.3 (01), 4.5 (10) and 4.7
(11) GHz. For example, the slotted resonator with gap of
2 mm will produce bit of 0000000000. To improve the
number of bits per slotted notch resonator, the allocation of
resonant frequencies is added in a specific frequency range.
However, the mutual coupling between resonators is to be
considered to avoid the overlapping of resonant frequen-
cies between multiple MCSRRs.
Figure 6 shows the current distribution of CPW UWB
Fig. 3 S11 results of the proposed antenna and conventional notch antenna with integrated MCSRRs. The strong current dis-
antenna (five notch UWB slotted antenna) tribution occurs at the first ring, second ring and third

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48 Page 4 of 5 M. E. Jalil et al.

(a) 4.1 GHz (b) 5.2 GHz

(a) 4 GHz

(c) 6.1 GHz (d) 7.1 GHz

(b) 5 GHz

(e) 8.1 GHz

Fig. 6 Current distribution at five different frequency bands (4.1, 5.2,

6.1, 7.1 and 8.1 GHz)

slotted ring of patch which provides notch bands at 4.1, 6.1

(c) 6 GHz
and 8.1 GHz. The same phenomena occur for the slotted
ground plane which provide band notches at 5.1 and
7.1 GHz.
Figure 7 illustrates the 3-D radiation pattern for 4, 5, 6,
7 and 8 GHz at each of the y–z and x–z planes. Near-
omnidirectional patterns are produced at all the notch band
frequencies. As shown in the figures, the value of direc-
tivity produced is about 3.98 to 6.61 dBi at 3 to 8 GHz.
(d) 7 GHz
2 Conclusion

A novel RF barcode tag using monopole antenna with

modified complementary split ring on fleece substrate that
operates between 3.0 to 12.0 GHz with 10 bits of data has
been designed and analyzed. The concept of modified
complimentary split ring resonator is proposed to minia-
turize the size and reduce the space consumption for (e) 8 GHz
chipless RFID application. The compact, flexible and

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 Flexible ultra-wideband antenna incorporated with metamaterial structures: multiple notches… Page 5 of 5 48

b Fig. 7 Radiation patterns of the proposed antenna at 4.0, 5.0, 6.0, 7.0 material, in 2012 International Symposium on Antennas and
and 8.0 GHz Propagation (ISAP), pp. 30–33 (Nagoya, 2012)
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absorber based on circular ring structure with and without copper
lines. Appl. Phys. A 117(2), 651–656 (2014)
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5. J. Carver, V. Reignault, F. Gadot, Engineering of the metama-
designs will be measured with two reference antennas for terial-based cut-band filter. Appl. Phys. A 117(2), 513–516
radio cross-section (RCS) measurement and S21 insertion (2014)
loss as future work. 6. S. Preradovic, N.C. Karmakar, Design of fully printable planar
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Acknowledgements The authors would like to thank the Ministry of
2009)
Higher Education (MOHE), IETR Lab of University of Rennes 1,
7. S. Preradovic, N.C. Karmaka, Low Cost Chipless RFID Systems,
Research Management Centre (RMC), School of Postgraduate Studies
Multiresonator-Based Chipless RFID (Springer, New York,
(SPS), Communication Engineering Department, Faculty of Electrical
2012), pp. 9–24
Engineering (FKE), and Universiti Teknologi Malaysia (UTM), Johor
8. Y.F. Weng, S.W. Cheung, T.I. Yuk, L. Liu, Design of chipless
Bahru, for the support of the research under Grant Nos. 4L811 and
UWB RFID system using a CPW multi-resonator. IEEE Anten-
05H35. The authors also would like to acknowledge all members of
nas Propag. Mag. 55(1), 13–31 (2013)
Advanced RF and Microwave Research Group (ARFMRG).
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