IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS 959
Ultrawideband Antenna With Triple Band-NotchedCharacteristics
Using Closed-Loop Ring Resonators
Mohammad Almalkawi, Student Member, IEEE, and Vijay
Devabhaktuni, Senior Member, IEEE
AbstractThe design of a simple multilayered triple band-notched
ultrawideband (UWB) antenna is presented in thisletter. The
proposed antenna is compact in size, suitable forultrawideband
applications, and exhibits triple narrow frequencyband notches to
suppress the interference of the nearby wirelesscommunication
systems within a UWB frequency range. Thenarrow band notches are
realized by adding closed-loop ringresonators designed to cover the
3.33.7-GHz, 5.155.35-GHz,and 5.7255.825-GHz bands. The center
frequencies of theband notches can be adjusted by varying the ring
resonatorsmean diameters. The designed antenna has a compact
volumeof 33 30 1.524 mm . The antenna is fabricated and
testedproviding broadband impedance matching, appropriate gain,
andstable radiation pattern.
Index TermsClosed-loop ring resonators, multilayered,
tripleband-notched, ultrawideband (UWB) antenna.
I. INTRODUCTION
R ECENTLY, there has been increasing demand in de-signing
ultrawideband (UWB) systems, and more partic-ularly so after the
release of the frequency band 3.110.6 GHzby the Federal
Communications Commission (FCC) [1]. Themain objective of UWB is
the handling of high data ratesin the presence of wireless
communication standards, whichcause electromagnetic (EM)
interference with the UWB sys-tems, such as the Worldwide
Interoperability for MicrowaveAccess (WiMAX) system operating at
3.33.7 GHz andwireless local area network (WLAN) system operating
at5.155.35 and 5.7255.825 GHz. Since antennas are
essentialcomponents for a host system application, it is desirable
todesign UWB antennas that comprise narrow band notcheswithin the
UWB frequency range. The early works on fre-quency band-rejected
UWB antennas were realized by utilizingsmall strip bars [2][4], an
open-loop resonator [5], U-shapedslots [6][8], an -shaped slot [9],
a half-mode substrate inte-grated waveguide cavity [10], and a
pentagonal radiating patchwith two bent slots [11]. In [2][9],
however, the elementswere developed on the same layer within the
antenna radiatoror on the back side of the same layer for
generating single-
Manuscript received August 26, 2011; accepted September 01,
2011. Date ofpublication September 12, 2011; date of current
version October 03, 2011. Thiswork was supported in part by the
EECS Department and the College of Engi-neering of the University
of Toledo, Toledo, OH, under graduate assistantshipsand a startup
grant, respectively.The authors are with the Electrical Engineering
and Computer Science De-
partment, University of Toledo, Toledo, OH 43606 USA (e-mail:
[email protected]).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.2011.2167649
Fig. 1. Structure of the proposed triple band-notched UWB
antenna in threelayers configuration. (a) 2-D double-sided view of
each layer. (b) Top view.(c) Side view.
and/or dual-frequency band-notched antennas. Therefore, dueto
the space limitation, it is difficult to generate multiple
bandnotches. On the other hand, in [10] and [11], the designs
havecomplicated structures leading to increased fabrication
costs,antenna size, and difficulty in the integration with
microwaveintegrated circuits.The objective of this letter is to
present a simple and com-
pact realization with stable radiation performance of a
tripleband-notched planar antenna suitable for UWB applications.
Itwill be shown that the proposed antenna in Fig. 1 possessesthe
desirable feature of compactness while achieving an accept-able
impedance bandwidth performance. Closed-loop ring res-onators have
been utilized because of their narrow bandwidth,compact size, and
low radiation loss [12] essential to ensuringrelatively
omnidirectional far-field radiation pattern (which is
1536-1225/$26.00 2011 IEEE
960 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
originally due to the actual rectangular slot patch
monopoleantenna).The organization of this letter is as follows.
Section II de-
scribes the configuration of the proposed antenna. Section
IIIpresents measured and simulated results, while conclusions
aregiven in Section IV.
II. ANTENNA CONFIGURATIONThe monopole UWB antenna illustrated in
Fig. 1, top side of
layer 3, is realized using a rectangular slot patch with a 50-
mi-crostrip feed line. Triple-frequency band notches are achievedby
vertically aligning three ring resonators (with their
centersaligned along an axis) on multilayered planes. Here, each
ringis responsible for creating a frequency band notch.The antenna
is printed on three layers of Rogers substrate
(RO4003) with a dielectric constant of 3.55 and a loss tangentof
0.0027. The thicknesses of the layers have been arbitrarily
se-lected, and each layer has a thickness of 0.508 mm as
illustratedin Fig. 1(c). The antenna is connected to a 50- SMA
connectorbetween the feed line on the top side of layer 3 and the
groundplane on the bottom side of layer 1.Full-wave EM simulations
are performed using ANSYS-
HFSS [13], leading to the following optimal dimensions for
theproposed antenna: mm, mm, mm,
mm, mm, mm, mm,mm, mm, mm, mm,mm, mm, mm, mm,mm, mm.
In this design, the fundamental stopband center
frequencycorresponding to each ring is approximately given by
(1a)
Therefore
(1b)
where is the mean diameter of the ring, is the guided
wave-length, is the speed of light in free space, and is the
ef-fective relative dielectric constant. The arrangement of the
ringresonators could be either above and/or below the actual
an-tenna radiator. Each ring in the structure resonates at
differentresonant frequencies by varying the mean diameter. Rings
onthe top and bottom side of layer 1 are responsible for
generatingthe rejection bands for upper WLAN and WiMAX
standards,respectively, while the ring on top of layer 2 is
responsible forgenerating the rejection band for the lower WLAN
standard.
III. EXPERIMENTAL RESULTS AND DISCUSSIONSIn this section,
parametric studies have been carried out using
ANSYS-HFSS for providing a better understanding of the an-tenna
operation. Moreover, measured impedance bandwidthand radiation
pattern are discussed. For convenience, resultsin Figs. 2 and 3
have been obtained using one ring resonatorlocated on the top side
of layer 2, with the other resonatorsremoved.Fig. 2 shows the
variation of the VSWR with frequency for
different mean diameters of the ring resonator. Increasing
the
Fig. 2. Simulated VSWR versus frequency by varying mean diameter
of thering resonator located on the top side of layer 2.
Fig. 3. Simulated VSWR versus frequency by varying the axial
position alongthe -direction and adjusting both width andmean
diameter of the ring resonatorlocated on the top side of layer
2.
Fig. 4. Measured and simulated VSWR performance of the proposed
antenna.
TABLE ICALCULATED AND OPTIMIZED RING RESONATORS
PARAMETERSCORRESPONDING TO THE REJECTED CENTER FREQUENCY
AND THE REQUIRED BANDWIDTH
mean diameter of the ring resonator leads to negative shift
inthe resonant frequency.
962 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
Fig. 6. Measured and simulated gains of the proposed antenna
versus fre-quency.
Fig. 7. Photograph of the fabricated antenna. (a) Top view. (b)
Bottom view.
the measured radiation patterns of the proposed antenna along-,
-, and -planes at 4, 7, and 9 GHz, respectively. The-plane (i.e.,
-plane) patterns are almost omnidirectional forthe three
frequencies, in a manner similar to the conventionaldipole antenna.
On the other hand, the -plane (i.e., -plane)patterns are relatively
similar to those of a monopole.Fig. 6 shows themeasured and
simulated antenna gains, while
Fig. 7 shows a photograph of the fabricated antenna. The gainwas
measured at the broadside direction as shown in Fig. 6,where two
identical antennas are separated by a distance of0.98 m. The
transmission coefficient was measured after afull two-ports
calibration was carried out to a Rhode & SchwarzZVB20 vector
network analyzer (VNA) and used to calculatethe antenna gain using
the following formula [15]:
(2)
where , are respectively the transmitter and receiver gainand
are equal in this case. , are the transmitted and re-ceived powers,
and is free-space wavelength in meters.It is observed that the
average gain of the proposed antenna is
about 24.5 dB over the entire operating band, exhibiting
gen-eral flat gain performance. As well, it is clearly evident that
atthe notch bands, the antenna gain drops sharply.
IV. CONCLUSION
A compact and simple multilayered triple band-notchedUWB antenna
for WiMAX and lower/upper WLAN appli-cations has been proposed. The
overall antenna volume is
33 30 1.524 mm . The antenna radiator design comprisesa
rectangular slot patch fed with a 50- microstrip line.Triple
band-notched frequencies are realized by adding threeclosed-loop
ring resonators sharing the same vertical axial andimplemented on
multiple layers. Having the ring resonatorssharing the same
vertical axis led to straightforward fabrication.The antenna has
been fabricated and measured for the purposeof validating our
design. The performance of the proposedantenna exhibits a good
impedance matching and radiationperformance.It is therefore
possible to conclude that the presented antenna
will prove advantageous inmodernmultilayeredmicrowave cir-cuits
such as microwave monolithic integrated circuits (MMIC)or
low-temperature co-fired ceramic (LTCC) technologies.
ACKNOWLEDGMENT
The authors would like to express their gratitude toDr. M. Alam,
Chair of the EECS Department, Universityof Toledo, Toledo, OH.
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