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C 2017 Wiley Periodicals, Inc.
V
AN ELECTRICALLY SMALL SICRR
METAMATERIAL-INSPIRED DUAL-BAND
ANTENNA FOR WLAN AND WiMAX
APPLICATIONS
Sameer Kumar Sharma,1 Mahmoud A. Abdalla,2 and
Raghvendra Kumar Chaudhary3
1
Department of Electrical Engineering, Indian Institute of Technology
Kanpur, Kanpur 208016, India; Corresponding author:
sharma.sameer16@gmail.com
2
Department of Electronic Engineering, Military Technical College,
Cairo, Egypt
3
Department of Electronics Engineering Indian School of Mines
Dhanbad, Dhanbad 826004, India
Received 21 August 2016
ABSTRACT: This study presents the design of an electrically small
metamaterial antenna with dual-band characteristics for WLAN and
WiMAX applications with coplanar ground. The proposed antenna consists of stepped-impedance closed ring resonator (SICRR) and a small
rectangular patch which is designed by etching a split ring resonator
(SRR) from a rectangular patch which is turn fed through main feed.
Such metamaterial composite exhibits dual-band behavior with first
band operating at 2.45 GHz with an impedance bandwidth (|S11| < 210
dB) of 8.16% while second band is resonant at 3.37 GHz having an
impedance bandwidth of 23.74% respectively. The proposed antenna is
designed specifically to operate at WLAN (2.5 GHz) and WiMAX
(3.5 GHz) and shows compact nature with a radiating element size of
0.16ko 3 0.097ko 3 0.013ko. Equivalent circuit of proposed antenna
has also been modeled which is in good agreement with the antenna
behavior. The proposed structure shows end fire radiation pattern in Hplane and omni-directional radiation pattern in E-plane at all operating
frequencies with low cross polarization levels. The prototype has been
fabricated and experimentally tested to validate the simulation results
DOI 10.1002/mop
which are in good agreement with the measured results. The antenna is
C 2017 Wiley
suitable for use in Bluetooth, WLAN and WiMAX. V
Periodicals, Inc. Microwave Opt Technol Lett 59:573–578, 2017; View
this article online at wileyonlinelibrary.com. DOI 10.1002/mop.30339
Key words: dual band; electrically small antenna; metamaterials;
WLAN/WiMAX
1. INTRODUCTION
Recent trends indicate that a lot of research is being carried out
in order to miniaturize antennas in wireless applications. These
antennas have low profile and can facilitate easy integration
with complex circuitries. Various microstrip multi band antennas
have been reported recently which can operate at desired wireless standards. These multi-band antennas have been rigorously
investigated by loading slots [1] or shorts [2] or using multiple
resonating elements [3] for achieving multi-band characteristics.
However, their use in small units is mainly restricted by large
size and poor bandwidth as they are of the order of half wavelength [4]. Metamaterials (MTMs) on the other hand have
emerged as a handsome solution to this problem. They are artificially engineered structures which offer unusual characteristics
of negative permittivity and negative permeability and have a
size less than quarter wavelength [5]. Split ring resonator (SRR)
and complimentary split ring resonator (CSRR) provide munegative (MNG) and epsilon-negative (ENG), respectively, and
are essential parts to constitute left handed metamaterial (LHM)
[5,6]. Such MTM inspired antennas have been widely adopted
for designing multi-band antennas and shrinking the antenna
size [7–10]. Unfortunately, bandwidth of these electrically small
antennas is basically limited by the lower bound on quality factor which was studied by Chu and later re-examined by Mc
Lean [11]. As a consequence, MTM based antennas have an
acute problem of narrow bandwidth as they inherently have high
quality factor and thus, radiation efficiency is also on the lower
scale as well gain is negative. Therefore, bandwidth and gain
enhancement of such electrically small MTM antennas based of
TL has been one of the main research subjects from past few
years. An attempt for enhancing the bandwidth is done by
decreasing the shunt capacitance but, the overall size of the
antenna is on the higher end [12,13]. Another bandwidth
enhancement technique has also been presented by the authors
by using a secondary ground plane below the radiating element
and loading an electromagnetic band gap (EBG) structure on the
conventional ground plane of CPW-fed ENG TL based bow-tie
shaped antenna [14]. Stepped-impedance resonators (SIRs) have
also been quite popular in MTM based antennas for their advantages of size reduction, harmonic suppression and low insertion
loss [15,16].
In this article, an electrically small antenna has been
designed to operate at WLAN and WiMAX and offers dualband characteristics. Coplanar ground plane has been used as it
allows size reduction as compared to CPW-fed structures. A
SRR has been etched from rectangular patch to form steppedimpedance complementary ring resonator (SICRR) and a small
patch separated by CSRR. Analysis has been carried out on
SICRR in order to decrease the high inductance of thin line of
the CSRR for tuning the resonance of first band at 2.45 GHz.
Equivalent circuit model has also been proposed and theoretical
expression of resonance frequencies for both bands has been
qualitatively expressed based on distributed values by visualizing the surface current plots. The novelty of the work can be
concluded from the fact that proposed antenna offers a very
compact size is motivated from design equations of ENG
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 59, No. 3, March 2017
573
Figure 1 (a) SRR in SIR configuration (model 1), (b) The SRR in SIR configuration (model 2). [Color figure can be viewed at wileyonlinelibrary.
com]
Figure 2 (a) Geometry of proposed unloaded antenna (b) Geometry of proposed metamterial-inspired CSRR loaded antenna (L 5 40, W 5 12, Wg 5 18,
W1 5 8, Wf 5 2.4, g 5 0.4, L1 5 15, L2 5 5.8, L3 5 3.8, Lp 5 5.6, T1 5 0.4, T2 5 2.5, T3 5 40, Wp 5 5.6, All dimensions are in mm), (c) The simulated
reflection coefficient of the proposed antenna (unloaded and loaded with the CSRR particle). [Color figure can be viewed at wileyonlinelibrary.com]
transmission line and SIRs. Simulation work has been carried
out using Ansys HFSS and prototype antenna has been experimentally tested.
2. ANTENNA DESIGN
In this section, we explain the design procedures for the proposed antenna. The design of the antenna is based on etching
stepped impedance split ring resonator (SISRR) from a rectangular patch. Accordingly, additional resonance of the unloaded
antenna (dual band functionality) has been achieved with small
size. The suggested SISRR geometry is shown in Figure 1(a) as
model (1). In Figure 1(b), the middle strip in the SISRR cell has
been replaced by two identical at top/bottom for later etching.
The configuration of the proposed antenna with unloaded rectangular patch fed by main feed is shown in Figure 2(a). On the
other hand, the proposed antenna where the patch is loaded with
the SICRR is shown in Figure 2 (b). The detailed cell dimensions have been obtained via parametric analysis and fine tuning. The proposed antenna has been designed on FR4 epoxy
substrate (er 54.4, tan d 5 0.02) with thickness 1.6 mm. The
overall size of the antenna is 40 3 12 mm2. The simulated input
reflection coefficients of the loaded/unloaded proposed antennas
are shown in Figure 2(c). It can be concluded that an extra band
is obtained by loading a CSRR on a rectangular patch which
operates at 2.45 GHz.
The equivalent circuit model of proposed antenna based on
epsilon negative (ENG) transmission line is shown in Figure 3.
ENG TL is a modified form of CRLH transmission line where
574
series capacitance is not present and different lumped elements
are realized for its formation. In the model, C1 and C2 are the
inherent shunt capacitances due to asymmetric CPW-feed while
L1 is the inductance offered by the main feed line. L2 and L3 are
the inductors formed by thin strip connecting main feed with
rectangular patch and rectangular patch itself while L4 and L5
are the inductances due to stepped-impedance closed ring resonator (SICRR) respectively. In addition, C3 is capacitance due
to gap between low impedance line of SICRR and inner rectangular patch while C4 is the coupling capacitor arising due to gap
between high impedance line of SICRR and inner element.
The surface current density of proposed antenna is shown in
Figures 4(a) and 4(b) at 2.5 GHz and 3.5 GHz respectively. It
can be seen that at 2.5 GHz, there is a strong current in main
feed line and high impedance line and by qualitative analysis, it
Figure 3 Equivalent circuit model of proposed metamaterial-inspired
antenna based on ENG TL
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 59, No. 3, March 2017
DOI 10.1002/mop
Figure 4 The simulated surface current density of proposed antenna, (a) at 2.5 GHz, (b) at 3.5 GHz. [Color figure can be viewed at wileyonlinelibrary.com]
can be predicted that lumped elements L1, L2, L4, C1, and C2
are responsible for this resonance while effect of others can be
ignored which is well supported by parametric analysis. Thus,
resonant frequency at first band (f1, band) can calculated as
1
f1;band 5
2p
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1
ðC1 丣C2 Þ½L1 1ðL2 jjL4 Þ
(1)
where 丣 is indicative of series combination and jj is indicative
of parallel combination. It can also be inferred that at 3.5 GHz,
current is mainly concentrated in the main feed line and line
connecting inner patch with feed and using the similar analysis
as above, it can analyzed that resonance frequency of second
band (f2, band) can be written as
1
f2;band 5
2p
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1
ðC1 丣C2 Þ½L1 丣L2 (2)
3. ANTENNA PARAMETRIC STUDY
The performance of the antenna can be explained in this section
by parametric study of the SICRR unit cell. Figure 5(a) shows
the variation in input reflection coefficient with change in thickness “T2” and in turn impedance Z2. It can be seen that by
increasing the impedance Z2 by lowering T2, resonant frequency
of first band gets shifted towards the left side with deterioration
in impedance matching while second band is almost unaffected.
Figure 5(b) shows the variation in input reflection coefficient
Figure 5 The simulated input reflection coefficient of proposed antenna (a) with change in thickness (T2), (b) (a) with change in gap “g”. [Color figure
can be viewed at wileyonlinelibrary.com]
DOI 10.1002/mop
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 59, No. 3, March 2017
575
Figure 6 The simulated input reflection coefficient of proposed antenna (a) with change in thickness “T3,” (b) with change in length of inner patch
“T1”. [Color figure can be viewed at wileyonlinelibrary.com]
with change in gap “g” between ground plane and CPW-feed.
In other words, by decreasing “g,” capacitance C1 increases,
thus according to Eqs. (1) and (2), resonant frequencies must
shift towards left. However, it is to be noted that C2 is very
strong as compared to C1 for case the first band while for second band C1 is negligible while C2 is strong. Thus, it can be
analyzed that variation in “g” must have a stronger impact on
second band as compared to first band which can also be interpreted from Figure 5(b). Using this point, bandwidth of second
band (BW2,band) can be easily evaluated in terms of lumped elements and is shown in Eq. (3) where G is the conductance.
Thus, ground plane has a considerable effect on the bandwidth
of second band only. Thus, with increase in g, ground plane size
decreases which results in increment of bandwidth.
sffiffiffiffiffiffiffiffiffiffiffiffiffiffi
L1 丣L2
BW2;band 5G
(3)
C1
Variation in input reflection coefficient with change in feed
width “T3” of proposed antennas is shown in Figure 6(a). It is
seen that with decrease in feed width, resonant frequencies for
both band decreases which matches well with Eqs. (2) and (3)
as L1 and L2 are increased. In Figure 6(b), the variation in input
reflection coefficient of proposed metamaterial with change in
Figure 7 (a) The measured and simulated input reflection coefficient of proposed antenna (b) A Photograph of fabricated prototype. [Color figure can
be viewed at wileyonlinelibrary.com]
576
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 59, No. 3, March 2017
DOI 10.1002/mop
Figure 8 The measured and simulated radiation patterns of proposed metamaterial-inspired antenna (a) E-plane at 2.5 GHz, (b) E-plane at 3.5 GHz,
(c) H-plane at 2.5 GHz, (d) H-plane at 3.5 GHz. [Color figure can be viewed at wileyonlinelibrary.com]
thickness of stepped-impedance closed ring resonator “T1” is
illustrated. It is worth noticing that there is only a slight change
in resonance frequency of first band while second band is almost
unaffected. As, T1 decreases inductance L4 increases and as a
result there is a very small change in resonant frequency. This is
attributed to that fact that with change in T1, capacitance C2 also
changes which tries to compensate the change in L4. Though, the
effect of C2 is quite small but its effect cannot be ignored. Similarly, when length of rectangular patch Lp is increased by keeping
DOI 10.1002/mop
gap between patch and low impedance line of SICRR constant,
L2 is decreased. However, the capacitance C4 becomes quite
prominent in such a case and its effect cannot be ignored and
thus, there is no major change in resonant frequencies.
4. ANTENNA EXPERIMENTAL RESULTS
Figure 7(a) shows the simulated and measured input reflection
coefficient of proposed antenna. It can be seen that proposed
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 59, No. 3, March 2017
577
metamaterial antenna exhibits dual-band characteristics with first
band resonant at 2.45 GHz offering an impedance bandwidth
(|S11| < 210 dB) of 8.16% while second band resonant at
3.37 GHz with an impedance bandwidth of 23.74% which is in
strong agreement with simulated results. However, due to problem in fabrication, thickness T3 is not maintained as 0.4 mm
which is responsible for a slight shift in frequency. The fabricated
antenna shows compact nature and has a radiating element size
of 0.16 ko 3 0.097 ko 3 0.013 ko and is shown in Figure 7(b).
Chu limit [9] is the theoretical limit on bandwidth for electrically
small antennas and is determined by the lower bound on quality
factor. Thus, it is quite useful to compare the measured bandwidth of proposed antenna and theoretical limit which is given in
Eq. (4). Later, Mc Lean re-examined this equation and gave an
accurate version of this Equation [10] which is given by Eq. (5)
Qmin 5
BWmax 5
1
ðkaÞ3
1
1
ka
VSWR21
pffiffiffiffiffiffiffiffiffiffiffiffiffi
Qmin VSWR
(4)
(5)
where Qmin is lower bound on quality factor, k is free space
propagation constant, a is the radius of sphere enclosing the
radiating element, VSWR is voltage standing wave ratio and
BWmax is maximum percentage bandwidth . For proposed antenna, k 5 51.06 rad/m at a center frequency of 2.45 GHz and
a 5 11.66 mm. Thus, ka 5 0.595 <1, which indicates that the
proposed antenna is electrically small. Now, Qmin 5 6.427 and
BWmax 5 11% for VSWR 5 2 which is 1.35 times of measured
bandwidth. Hence, measured bandwidth of proposed antenna is
within the achievable theoretical limits.
Finally, the simulated and measured radiation patterns of
proposed antenna at 2.5 GHz and 3.5 GHz, respectively, are
plotted in Figure 8. It can be seen that proposed metamaterial
antenna exhibits onmi-directional radiation pattern in E-plane at
both the frequencies with low cross-polarization levels. End fire
radiation patterns are observed in H-plane for both 2.5 GHz and
3.5 GHz which is due to the 90 degree phase difference between
CPW-feed and main feed line. The proposed antenna offers a
measured gain of 0.3 dBi with a simulated radiation efficiency
of 68% at 2.45 GHz and a measured gain of 1.1 dBi with a simulated radiation efficiency of 77.3% at 3.37 GHz respectively.
5. CONCLUSION
An electrically small asymmetrical CPW-fed metamaterialinspired antenna with dual-band characteristics has been presented for WLAN and WiMAX applications. The proposed
antenna offer compact nature with an overall antenna size of 0.32
ko 3 0.097 ko 3 0.013 ko and impedance bandwidth of 8.16%
and 23.74% at 2.45 GHz and 3.37 GHz respectively. SIRs were
employed to stabilize the resonant frequency of first band. Equivalent circuit of proposed antenna based on ENG transmission line
was modeled and analyzed. The proposed antenna exhibits omnidirectional radiation patterns in E-plane and end-fire radiation
patterns in H-plane for all operating frequency range. Small size,
low profile and excellent radiation characteristics make it suitable
for deployment in wireless circuitries.
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C 2017 Wiley Periodicals, Inc.
V
A NOVEL DOUBLE BALANCED IMAGEREJECTED MIXER FOR ULTRA-WIDE
BAND COMMUNICATION SYSTEMS
Xin Cao,1 Zongxi Tang,1 and Fei Wang2
1
School of Electronic Engineering, University of Electronic Science
and Technology of China, China; Corresponding author:
798899759@qq.com
2
Institute of Astronautics and Aeronautics, University of Electronic
Science and Technology of China, China
Received 23 August 2016
ABSTRACT: In this article, a novel double balanced image-rejected
mixer is proposed. To increase image-rejection, a novel power divider
based on quarter-wavelength resonators, a pair of radial-stub-loaded
coupled line filters, and a 3 dB RF quadrature microstrip/slot line coupler are employed in our design. The measurement is implemented using
the Rohde & Schwarz four-port vector analyzer. The measured results
show that, the conversion loss is less than 17 dB with the image rejection over 14 dB within the operating band from 3.1 GHz to 10.6 GHz.
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 59, No. 3, March 2017
DOI 10.1002/mop