This document describes a novel ultrawideband (UWB) printed antenna that exhibits dual complementary behavior. It can function as either a frequency notched UWB antenna or a narrowband antenna based on different combinations of split ring resonators (SRRs) and metallic strips loaded on the feed line. Simulation and measurement results on three prototype antenna configurations validate that loading SRRs produces a frequency notch response, while adding metallic strips transforms it into a narrowband response at the SRR resonance frequency. Shorting the SRR splits restores the original UWB response. The antenna provides tunability of the narrowband frequency by varying the SRR dimensions.

1. 974 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 14, 2015
A Novel Ultrawideband (UWB) Printed Antenna
With a Dual Complementary Characteristic
Jawad Y. Siddiqui, Senior Member, IEEE, Chinmoy Saha, Senior Member, IEEE, and
Yahia M. M. Antar, Life Fellow, IEEE
Abstract—A novel design concept for a versatile multi-functional
coplanar waveguide (CPW)-fed ultrawideband (UWB) printed an-
tenna is described in this letter. The antenna also exhibits a dual
complementary characteristic of frequency notched response and
narrowband response invoked by different combinative loading of
a pair of split ring resonators (SRRs) and metallic shunt strips on
the CPW feed line. The antenna restores its UWB response when
the SRRs’ split gaps are shorted. The simulated impedance and
radiation characteristics are validated with measured results ob-
tained using fabricated prototypes to establish the proof of concept.
Index Terms—Circular monopole, split ring resonator (SRR), ul-
trawideband (UWB) antenna.
I. INTRODUCTION
EMERGING needs like software defined radio (SDR) and
cognitive radio (CR) are redefining the design of wire-
less systems. Different multi-functional antennas are integrated
in such systems for efficient communication. Hall et. al. in [1]
have discussed the requirements and limitations of such an-
tennas used in CR and SDR. However, most of the proposed
configurations [2]–[4] involved two antennas with two ports,
each for wideband and narrowband communication, with addi-
tional isolation to avoid coupling. Hence, use of a single antenna
to achieve wideband and narrowband operation will have wide
implications in the growth of such systems.
Planar monopoles with finite ground planes are one of the
most widely used antennas for wideband operation [5]. Re-
cently, in [6], the present authors showed that a frequency notch
can be achieved in an UWB response of the printed monopole,
if the coplanar waveguide (CPW)feed is coupled with a pair
of SRRs. Compact microwave filters using SRRs on CPW has
recently been proposed in [7].
In the present work, a unique design concept is proposed
to demonstrate a complementary characteristic of a frequency
notched ultrawideband antenna to operate as a narrowband
antenna. This interesting phenomenon is achieved by placing
thin metallic shunt strips across the signal line and the ground
planes of the CPW, strategically aligned with the SRRs axes.
Manuscript received November 28, 2014; accepted December 22, 2014. Date
of publication January 01, 2015; date of current version April 21, 2015.
J. Y. Siddiqui is with the Royal Military College of Canada, Kingston, ON,
Canada K7K7B4 and also with the Institute of Radio Physics and Electronics,
University of Calcutta, Kolkata, 700019, India (e-mail: jys.rpe@gmail.com).
C. Saha is with the Department of Avionics, Indian Institute of Space Science
and Technology, Thiruvananthapuram, 695547, India (e-mail: csaha@ieee.org).
Y. M. M. Antar is with the Royal Military College of Canada, Kingston, ON,
Canada K7K7B4 (e-mail: antar-y@rmc.ca).
Color versions of one or more of the figures in this letter are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LAWP.2014.2388272
TABLE I
ILLUSTRATION OF DIFFERENT COMBINATIVE LOADING OF SRRS, CRRS AND
SHUNT STRIPS ON THE CPW FEED OF THE PRINTED CIRCULAR MONOPOLE
ANTENNA AND THEIR DIFFERENT CHARACTERISTIC RESPONSE
This transforms the frequency notched UWB response of the
antenna into a narrowband response exhibiting acceptable gain
and monopole type radiation.
Inductively coupled shunt strips on CPW were used as band-
pass filters in [8]. Similar bandpass filtering was demonstrated
with ‘left handed’ transmission line in [9]. The current work ex-
tends these concepts to a printed antenna and demonstrates the
bandpass and bandstop filtering in the radiator’s impedance and
radiation characteristics. It has also been demonstrated experi-
mentally in the present work that when the split gaps in the SRR
are shorted, thereby forming closed ring resonators (CRRs), and
without the shunt strips, the UWB response of the antenna can
be restored. The different combinative loading of SRRs, CRRs
and shunt wires invoking three operational states of the same
printed monopole antenna is summarized in Table I.
The concept has been experimentally verified in this letter
using three demonstrator antennas with different combinations
of SRRs pairs and metallic shunt strips. The novelty of the pro-
posed design lies in its uncomplicated configuration, scalability
and simplicity to invoke the desired antenna response. The notch
frequency and the narrowband frequency are dependent on the
physical dimension of the SRR geometry and hence are scalable.
It has also been demonstrated that the loading of SRRs has no
adverse effect on the radiation pattern as they do not affect the
radiation aperture directly.
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2. SIDDIQUI et al.: NOVEL ULTRAWIDEBAND PRINTED ANTENNA WITH A DUAL COMPLEMENTARY CHARACTERISTIC 975
Fig. 1. Schematic of a printed circular monopole fed by SRR coupled and shunt
strip shorted CPW (Configuration A): (a) Top view with SRR on bottom met-
allization (b) Side view with SRR separated by from the CPW fed Monopole
(c) Schematic of a CPW transmission line shorted with shunt strips of width
(d) Schematic of a unit cell square SRR.
II. ANTENNA TOPOLOGIES AND DESIGN RATIONALE
Three prototype antennas namely Configuration A, Configu-
ration B and Configuration C, having CPW feed with different
combinations of SRR and CRR loading with and without
metallic shunt strip have been designed and fabricated. Con-
figuration A as shown in Fig. 1(a) comprises a printed circular
monopole antenna of radius, , fed by a shunt strip shorted
CPW and coupled with a pair of SRRs. The CPW feed consists
of ground planes having width and , length and a
signal line of width, and length with symmetric gaps,
, between the ground planes and signal line. The antenna is
printed on a substrate having thickness and dielectric constant
as shown in Fig. 1(b). Fig. 1(c) shows the alignment of the
thin metallic shunt strips of width , shorting the signal line
with the ground planes. Two square shaped split ring resonators
having dimensions ‘ ’ which is half the external side-length
of the SRR, conductor thickness ‘ ’, separation between rings
‘ ’ and split gaps ‘ ’ and ‘ ’ as shown in Fig. 1(d), are
printed on the bottom or back side of the substrate. The center
of the shunt strips is positioned at a distance from
bottom edge of the substrate. For optimal excitation, the SRRs’
axes should be aligned with the centre of the CPW slots and
the shunt strips. A fabricated prototype of Configuration A is
shown in Fig. 2. Configuration B is similar to Configuration
A, but without the shunt strips as was used in [6], where as,
Configuration C is similar to Configuration B loaded with a
pair of closed ring resonators (CRRs) in place of SRRs. The
structural dimensions of the CRRs are similar to SRRs with
shorted split gaps ( ).
The propagating electric field vector in the CPW is polar-
ized along the plane of the SRRs and the magnetic field vector
is along the SRRs’ axes. The fundamental mode of the propa-
gating signal excites the SRRs at a frequency determined by the
Fig. 2. Fabricated prototype of a printed circular monopole fed by SRR coupled
and shunt strip shorted CPW (Configuration A) (a) Top view (b) Bottom view.
SRRs’ dimensions and the constitutive parameters of the host
substrate [9], [6]. The diamagnetic behavior of the SRRs in Con-
figuration B yields a frequency notch in the UWB antenna as
was discussed in [6]. Interestingly, when a metallic shunt strip is
placed on the CPW transmission line strategically aligned with
the SRRs axes, thereby effectively shunting the signal line with
the ground planes, as in Configuration A, the frequency notched
UWB response of the antenna is transformed into a narrow-
band response. Hence, the proposed Configuration A exhibits
a complementary phenomenon vis a vis to the frequency notch
response of the antenna in Configuration B. The position of the
shunt strips should be coincident with the SRRs’ axes and their
combination forms a bandpass filter and yields a sharp narrow
band response corresponding to the resonance frequency of the
SRR. If the SRRs are replaced with CRRs as in Configuration C,
that is with shorted split gaps ( ), the antenna re-
stores its UWB characteristic as has been verified in this work.
The closing of the rings effectively destroys the magnetic reso-
nance of the SRRs and restores transmission for the entire UWB
spectrum [10].
III. RESULTS AND DISCUSSIONS
The three prototypes were fabricated on Taconic sub-
strates having , and thickness
mm. The circular monopole having radius
mm and the CPW feed design having ground plane
length mm, width mm and feed gap
mm were common for all three prototypes. For Config-
uration A, a pair of SRRs having dimensions mm,
mm, mm and split gaps mm,
were printed on the other side of the substrate with their
axes coinciding with the slot lines in the CPW as shown in
Figs. 1 and 2.
The shunt strips having width mm, at
mm, are used to short the signal line of the CPW with
the ground planes. Configuration B was fabricated by removing
the shunt strips ( ) from Configuration A. Configura-
tion C was similar to Configuration B but with shortened split
gaps ( ) of the SRRs. The prototypes were designed
and simulated using a commercial EM Simulator [11] and val-
idated with the measured impedance and radiation characteris-
tics. Fig. 3 shows the comparison between the measured reflec-
tion coefficients of antenna Configuration A and antenna Con-
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3. 976 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 14, 2015
Fig. 3. Measured of the CPW fed Circular Monopole loaded with SRRs
only (Configuration B) and with SRRs and shunt strips (Configuration A). Pa-
rameters for Configuration A: mm, mm, mm,
mm, mm, mm, mm, mm;
SRR parameters: mm, mm, mm,
mm Shunt strip width mm, mm; Parameters for
Configuration B: same as Configuration A, with Parameters for Con-
figuration B: as in Fig. 2 with .
figuration B. For Configuration B, with the CPW fed monopole
antenna coupled only with a pair of SRRs, the response
yields a notch centered at 6.55 GHz which corresponds to the
resonance frequency of the SRR. On the other hand for Con-
figuration A, the introduction of shunt strips yields a pass band
response and a sharp narrowband characteristic is obtained at
6.59 GHz in the measured . The theoretical value of the res-
onance frequency as per the proposed formulation in [6] was
computed at 6.52 GHz. The figure validates the complemen-
tary behavior of antenna Configuration A and Configuration B,
where the notch and the narrowband response corresponds to
almost the same frequencies. Fig. 4 shows the simulated reflec-
tion coefficients of the CPW fed Circular monopole loaded with
SRRs and shunt strips (Configuration A) for variable SRR pa-
rameters. The shift in the narrowband frequency is achieved by
changing the SRR dimensions and without scaling the printed
monopole dimensions. SRRs having different values with
different ring separation, ‘ ’ and split gaps
values were simulated to achieve a wide tuning from 4.8 GHz
to 8.4 GHz. The four encircled plots show the variation in the
reflection coefficient with varying split gap dimension ‘ ’ (
mm, mm and mm) for a fixed set of ,
and . The variation of the narrow band operating frequency
due to the gap variation can be exploited by introducing a phys-
ical device like varactor to achieve practical reconfigurability.
The SRR variables provide significant flexibility only limited
by the width of the signal line to shift the narrowband reso-
nances over 50% of the UWB spectrum. The plot also vali-
dates the simulated result with the measured result for Config-
uration A. Fig. 5 shows the measured and simulated reflection
coefficients of the printed monopole antenna Configuration ,
where the CPW is coupled with CRRs which are basically SRRs
with shorted split gaps ( ). Shorting of the split gaps
effectively converts the split ring resonators into closed ring res-
onators thus nullifying its effect on the transmission line and
therefore restoring the ultra wideband response of the antenna
operating from 2.8 GHz to 11 GHz as seen from the figure. The
plot is also compared with the measured data obtained using a
conventional CPW fed printed circular monopole.
Fig. 4. Simulated of the CPW fed Circular Monopole loaded with SRRs
and shunt strips (Configuration A) for variable SRR parameters and compared
with measured prototype of Configuration A. Parameters as in Fig. 3 with SRR
strip width, mm and shunt strip width, mm.
Fig. 5. Measured and simulated of the CPW fed Circular Monopole loaded
with closed ring resonators (shorted split gaps, ) and without shunt
strips(Configuration C)compared with CPW fed monopole only without SSRs
and shunt wires. Parameters as in Fig. 3.
The measured radiation patterns for the fabricated prototype
of antenna Configuration A is shown in Fig. 6. The plot shows
the co- and cross- polarized beam patterns for the narrowband
SRRs and shunt strip coupled CPW fed planar monopole (Con-
figuration A) in the E ( ) and H( ) planes at 6.59 GHz.
The radiation patterns show good monopole type radiation for
the E-planes with good cross polar discrimination of at least
dB in and good omni directional pattern in the
H( ) plane. The maximum calibrated gain in the E( )
plane as a function of frequency for Configurations A and C are
depicted in Fig. 7. A gain of 3.1 dBi at 6.59 GHz was obtained
for the narrowband antenna (Configuration A) and the gain in
the other frequency range is suppressed to less than zero. This
again is complementary to the gain pattern for the frequency
notched antenna (Configuration B) where the calibrated gain is
well above 1 dBi except at the notch frequency where it drops
to dBi as shown in Fig. 7.
The complementary nature of the antenna configurations A
and B can be explained with more physical insight by observing
the magnitude of the Poynting vector along one of the slots of
feeding-CPW line of the antenna over the entire UWB band as
a function of the distance from the feed position as illustrated in
Fig. 8. As shown in Fig. 8(a), the diamagnetic behavior of the
SRRs at its resonance frequency prohibits propagation at that
frequency whereas the rest of the spectrum is transmitted along
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4. SIDDIQUI et al.: NOVEL ULTRAWIDEBAND PRINTED ANTENNA WITH A DUAL COMPLEMENTARY CHARACTERISTIC 977
Fig. 6. Measured co-polarized and cross polarized radiation patterns for (a)
plane (E-plane), and (b) plane (H-plane) of the narrowband antenna
(Configuration A) resonating at 6.59 GHz. Parameters as in Fig. 3.
Fig. 7. Measured maximum realized calibrated gain characteristic in the (
) plane as a function of frequency of the CPW fed Circular Monopole loaded
with SRRs and shunt strips (Configuration A) and CPW fed Circular Monopole
loaded with SRRs only (Configuration B). Parameters as in Fig. 3.
the slot, giving rise to a notched UWB response. However, with
the positioning of the shunt wire, which acts as an electrical wall
on the transmission line, the filtered energy over a narrow band
is propagated along the line and coupled to the antenna ensuring
a narrow band operation of the antenna. The rest of the energy
is reflected back to the input port as depicted in Fig. 8(b), with
the dashed line indicating the central position of the shunt
wire at a distance mm from the input port.
IV. CONCLUSION
A novel idea to yield three different and complementary oper-
ating states using a simple CPW fed printed monopole antenna
is proposed. It has been demonstrated that a frequency notched
UWB antenna using a pair of SRRs can be transformed into a
narrowband antenna by shorting the signal line with the ground
planes using shunt strips. Simple bond wires or thin conducting
tapes can be used to transform the antenna response. It has also
been demonstrated that closing the gaps in the SRR rings, re-
store the UWB response of the antenna. The concept could be
exploited by embedding proper high-speed solid state or RF
MEMS based switches to achieve reconfigurability in cognitive
radio and MIMO applications.
Fig. 8. Simulated contour plots of the magnitude of the Poynting vectors of the
propagating electromagnetic energy though the longitudinal dimension of one
of the slots as a function of frequency. (a) Antenna Configuration B. Parameters
as in Fig. 3 with . (b) Antenna Configuration A. Parameters as in Fig. 3.
(Plots are in uniform scale).
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