U-Slot Multiband Inkjet Printed Antenna
1
Paper-Based Inkjet Printed Tri-Band U-Slot Monopole
Antenna for Wireless Applications
Hattan F. Abutarboush, Member, IEEE and Atif Shamim, Member, IEEE

Abstract—
Realization of U-slot tri-band Monopole antenna
on a low cost paper substrate using inkjet printed technology is
presented for the first time. U-shaped slot is optimized to enhance
the bandwidth and to achieve tri-band operation of 1.57, 3.2 and
5 GHz with measured impedance bandwidths of 3.21%, 28.1%
and 36% respectively. The antenna is fabricated through a
metallic nanoparticle ink on a standard commercial paper. Thus
the antenna can be used to cover the GPS, WiMAX, HiperLAN/2
and WLAN. The antenna has a compact size of 12 × 37.3 × 0.44
mm3 leaving enough space for the driving electronics on the
paper substrate. The impedance bandwidth, current
distributions, radiation patterns, gain and efficiency of the
antenna have been studied through computer simulations and
measurements.
Index Terms— small antenna, U-slot antenna, inkjet antenna,
multiband antenna, paper antenna
I. INTRODUCTION
D
ESIGN of compact and low cost antennas to support
several standards simultaneously for wireless devices
has been an interesting research topic in industry and
academia. The antennas in future must support multiband
operations, demonstrate small form factors, provide ease of
integration with RF circuits and, most importantly, are low
cost. These characteristics can be achieved by using cheap
organic substrates such as paper or polymers and by
employing low cost fabrication methods such as inkjet
printing [1].
Inkjet printing process emerged as a low cost fabrication
process for electronics recently [2]. Inkjet printing can be used
on different substrates by depositing almost any material that
can be put into liquid form. Inkjet-printing is a direct-write
technology where the layout of the structure is printed directly
on the paper or the substrate whereas the other fabrication
methods require expensive masks and etching processes.
Inkjet printing on substrates such as paper can be run reel to
reel or roll to roll making the fabrication more cost effective
for mass production as compared to wafer by wafer
processing.
Different inkjet printed antennas have been reported recently
for UWB and RFID applications. For example in [3], an UWB
Manuscript received Aug. 2, 2012
Hattan F. Abutarboush and Atif Shamim are with Electrical Engineering
Program, Physical Sciences and Engineering Division, King Abdullah
University Of Science and Technology (KAUST), P.O. BOX 4700, Thuwal,
Saudi Arabia.
Email: Hattan.Abutarboush@ieee.org
inkjet-printed EBG array antenna is proposed with a 0.1-mmthick copper sheet and dimensions of 150 x120 mm2. Other
different antennas on paper are reported in [1] and [4].
However, they are design for UWB applications. Moreover,
different RFID antennas printed on paper using inkjet
technology have been reported in [5-6] and on Liquid Crystal
Polymer (LCP) substrate in [7]. An inkjet printed frequency
selective surface antenna has been reported in [8]. However,
this antenna is designed to operate at a high frequency band of
7.5 GHz.
The first U-Slot antenna was introduced in 1995 by Huynh
and Lee [9]. Since then, the design has been extensively
studied for different applications. U-Slot technique is known
to improve the impedance bandwidth by introducing air
substrate which increases the overall size of the antenna [1011]. Also, the U-Slot can be used to introduce a band notch in
an UWB antenna [12] or to demonstrate dual- or multiband
characteristics [13-16]. Here, we use the U-Slot technique to
introduce new bands and improve the bandwidth.
In this letter, a compact U-Slots antenna is proposed using
inkjet printing process on paper substrate for multiband
operations. The antenna employs two U-slot shapes to
generate two additional bands at low and high frequency
bands. It is optimized to operate within the Global Positioning
System (GPS), Wireless Local Area Network (WLAN), the
Worldwide Interoperability for Microwave Access (WiMAX)
and HiperLAN/2 applications. The novelties of the design
include i) use of U-slots technique to create two additional
bands without the need to increase the antenna size, ii)
improvement of the 5 GHz bandwidth by using the same Uslots, and iii) realization of the multiband antenna on a low
cost paper substrate using inkjet printed technology for the
first time. The antenna has the advantages of small size, low
profile and simple configuration. The low profile of the
antenna makes it a promising candidate for future compact and
slim wireless devices.
II. DESIGN PROCEDURE AND FABRICATION PROCESS
A. Structure and Dimensions
The structure of the proposed monopole antenna with
microstrip-feed is shown in Fig. 1 which consists of a
rectangular radiator, a 50-Ω microstrip feedline and a ground
plane. The antenna is designed on a paper substrate with a
thickness of 0.44mm, a dielectric constant of 3.2 and a loss
tangent of 0.05. The properties of the paper substrates and the
ink were intensively investigated in [1].
U-Slot Multiband Inkjet Printed Antenna
2
(a)
Fig. 1: Layout of proposed antenna
L
20
W
40
Table I: Key dimensions of proposed antenna in mm
L1
L2
L3
L4
13.6
9.175
2.3
6.5
W1
W2
W3
W4
12
4.9
2.5
1.325
L5
3.7
W5
3
A U-shaped slot is cut on the radiator to create a longer
current path to excite a narrow band for the GPS system and,
at the same time, to achieve two wide bands for WiMAX,
HiperLAN/2 and WLAN systems. The design of the antenna
is optimized using the high-frequency simulation software
(HFSS) with the main dimensions listed in Table 1.
B. Design Steps and Current Distributions
The design procedure can be described using Fig. 2 (a)-(b) as
follows.
Step 1: A monopole antenna with microstrip-fed as shown in
Fig. 2(a) is first designed to operate in a single band at
approximately 3 GHz and optimized in terms of minimizing
the reflection coefficient S11. The result is shown in Fig. 2(b)
and Table II.
Step 2: A large U-shaped slot is cut on the radiator as shown
in Fig. 2(a) to perturb the current path and so to create dualband operation. It can be seen from the result of Fig. 2(b) and
Table II that adding the large U-shaped slot creates a highfrequency band at around 5 GHz.
Step 3: A small U-shaped slot is cut on the radiator as shown
in Fig. 2(a). The result in Fig. 2(b) and Table II shows that
cutting a smaller slot add another band at 1.57 GHz in addition
to the two more frequency bands at around 3.2 and 5 GHz,
with significantly better matching for the 5GHz without
requiring to increase the antenna size. The antenna now has
three frequency bands, one narrow band at 1.57 GHz and two
wide bands as shown in Fig. 2(b) and Table II.
Although the antenna is optimised to operate at 1.57, 3.2 and 5
GHz, other set of frequencies could be achieved by optimising
the sizes of the U-Slots.
The behaviour of the antenna is further studied using current
(b)
Fig. 2: (a) Steps of designing proposed antenna and (b) S11 of the design steps
Step #
#1
Table II: Band generated from each step
Bands Generated
Single band at 3 GHz
#2
Dual-band at 3 and 5 GHz
#3
Proposed
Dual-band at 3 and 1.57 GHz
Tri-Band at 1.57, 3 and 5 GHz
(a)
(b)
(c)
Fig. 3: Simulated current distribution at (a) 1.57, (b) 3.2 and (c) 5 GHz
distribution. The resonant frequencies of 1.57, 3.2 and 5 GHz,
have been used for these simulations. The result on current
distribution in Fig. 3(a) shows that, at 1.57 GHz, a current path
is formed along the edge of the complete small U-Slot and the
right hand arm of the large U-Slot. At the frequency of 3.2
GHz, Fig. 3 (b) show that the current concentrates more at the
edges of the middles gap between the large and the small USlot. At 5 GHz, Fig. 3(c) shows that the current concentrates
more at the bottom edge of the large U- Slot.
U-Slot Multiband Inkjet Printed Antenna
(a)
3
(b)
Fig. 4: Fabricated prototype of antenna (a) Top view and (b) Bottom view
Fig. 5: Simulated and measured results for S11
Table III: Simulated and measured bandiwdth
C. Fabrication Process
The fabricated antenna is shown in Fig. 4. A conductive
silver ink, with about 10nm size nano-particles dispersed in
a hydrocarbon solvent from UT Dots Inc., has been utilized
in this work. The conductivity of the ink achieved to print
the antenna is 1.2 e7 s/m. The ink conductivity improves by
adding more number of layers, but only up to a certain
number. For the inkjet printing process utilized in this
work, this number is limited to 5 layers, after which the
conductivity does not increase significantly.
The printing process starts with mounting the paper on the
printer and specifying the number of layers in the software.
Once the printing is done, the paper is left in the oven with
160 oC for about one hour to sinter (heating of
nanoparticles so that they melt and form a continuous track
on the paper).
The thickness of a single layer of the paper is 0.22 mm. The
radiator was fabricated on one layer whereas the ground plane
was fabricated on another layer. Most of the designs reported
in literature are based on a single layer to avoid the alignment
issues. However, in this work, alignment marks have been
placed on the edges of each layer and then both layers are
accurately glued to form a single layer of thickness 0.44mm2.
III. MEASURED RESULTS
The simulated and measured reflection coefficients S11 of
the antenna is shown in Fig. 5. The simulated and measured
results show good agreement. The small discrepancies can be
attributed to the fabrication and measurement tolerances. It
can be seen that the antenna can operate in three distinct
frequency bands centred at 1.57, 3.2 and 5 GHz. The
simulated and measured impedance bandwidths (S11<-10dB)
for the tri-band are summrised in Table III. These frequency
bands cover the GPS (1.57 GHz) at low frequency, and also
the bands for WiMAX standards of band I (2.6-2.7 GHz),
band II (3.4-3.69 GHz) and band III (5.25-5.85 GHz), and 5-
1.57 GHz
3.2 GHz
5 GHz
Simulated B.W
Measured B.W
3.21%
(1.53–1.58 GHz)
28.8%
(2.64 - 3.53 GHz)
29.1%
(4.42-5.93 GHz)
3.21%
(1.53–1.58 GHz)
28.1%
(2.75–3.65 GHz)
36%
(4.25–6.12 GHz)
GHz WLAN IEEE 802.11 a/n (5.150-5.350 / 5.725–5.825
GHz), and HiperLAN/2 (5.470–5.725 GHz).
The simulated and measured radiation patterns for co- and
cross-polarizations in the E-and H- planes at the frequencies of
1.57, 3.2 and 5 GHz are shown in Fig. 6 (a)–(c), respectively.
The antenna is measured using the antenna measurement
equipment, StarLab, manufactured by Satimo.
It can be seen that the normalized radiation patterns for the Eand H- cuts are quite stable throughout these frequencies
showing a low level of cross polarization. The antenna has a
monopole-shape radiation pattern in the E-plane and an
omnidirectional radiation pattern in the H-plane. A quite high
cross polarization at 5 GHz (E-plane) is observed, which is
due to the contribution of the surface current on the antenna in
the X-direction [17]. The discrepancy between the simulation
and measurements could be due to the effect of connector and
manufacturing tolerance. Moreover, since the size of the
antenna is small, the coupling between the connector and
various parts of the antenna may slightly affect the
performance. The simulated and measured realized gain along
with the S11 is displayed in Fig. 7. The curve of the measured
realized gain follows a similar trend as that of the simulated
realized gain. The measured realized gain is -6 dBi for the
lowest frequency which is expected due to the small size of
the antenna as compared to its size at 3 and 5GHz. The gain
for the 5 GHz band is ranged between 0 and 2 dBi. However,
the measured realized gain is slightly less than 1 dB
discrepancy over the 3.2 band. Considering the small cracks
that were noticed on some part of the radiators, the uneven
surface and the lossy nature of the paper (loss tangent ~0.05),
U-Slot Multiband Inkjet Printed Antenna
E-Cut
(a)
4
H-Cut
Fig. 7: Simulated and measured realized gain and S11 of proposed antenna
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Fig. 6: Simulated and measured co- and cross-polarizations for E- and H- cuts
at (a) 1.57, (b) 3.2 and (c) 5 GHz
[9]
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3.2-GHz and 5-GHz bands, respectively.
[10]
[11]
IV. CONCLUSIONS
The design of an inkjet printed multiband monopole antenna
with a compact size of only 12 × 37.3 × 0.44 mm3 has been
presented. U-shaped slot cut on the main radiator is used to
generate a low frequency band for GPS and two other high
frequency bands with much wider bandwidths for many other
applications. Although the proposed antenna is optimized to
operate at 1.57, 3.2 and 5 GHz, other applications are also
possible to be obtained by changing the structural parameters
of the U-Slot. The specific challenges encountered during this
work are, 1) using multi layers of papers where alignment is of
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soldering) and characterizing these antennas [1]. The small
size, light weight and the cost effectiveness of the proposed
antenna makes it suitable for small and slim wireless devices.
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