notched band uwb antenna

1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 61, NO. 8, AUGUST 2013 3961
A Compact Notched Band UWB Slot Antenna With
Sharp Selectivity and Controllable Bandwidth
Qing-Xin Chu, Senior Member, IEEE, Chun-Xu Mao, and He Zhu
Abstract—A compact ultra-wideband (UWB) slot antenna with
band-notched characteristics is proposed. A stepped slot is adopted
as a radiator to realize UWB impedance matching and reduce the
antenna size. By slitting an open-ended quarter-wavelength split
slot on the back of the feed and a short-ended half-wavelength
split-ring slot near the stepped slot, a second-order notched band
of 5.15–5.85 GHz is achieved. Compared with the traditional band-
notched antenna, the selectivity of the notched band is greatly im-
proved and size of the antenna is reduced at the same time. The
volume of the antenna is only .
Besides, the bandwidth can be easily controlled by adjusting the
lengths of the two slots respectively. Good agreement is achieved
between simulated and measured results, which show that the pro-
posed antenna has nice impedance matching and radiation pattern
characteristics.
Index Terms—Bandwidth controllability, compact size, roll-off
criterion (ROC), second-order notched band, stepped slot, UWB
antenna.
I. INTRODUCTION
SINCE the Federal Communication Commission (FCC) first
approved rules of 3.1–10.6 GHz for the commercial use
of ultra-wideband (UWB) communication in 2002 [1], the re-
search on UWB communication has achieved an unprecedented
rapid development. Based on the non-carrier wave communi-
cation technique, UWB communication has attracted more and
more people’s attention for its inherent advantages, such as high
data rate, low power consumption and low cost. UWB commu-
nication is likely to become the next generation of short distance
communication.
However, some wireless communication systems are also op-
erating in the UWB range, such as wireless local area network
(WLAN), operating at 5.15–5.825 GHz. It is necessary to elimi-
nate the frequency interference between these wireless commu-
nication systems and UWB system. As the RF front-end part and
important component, UWB antennas with notched bands have
become a research hotspot in recent year. Various band-notched
antennas were proposed in the past several years [2]–[22]. The
methods of realizing notched band usually include etching var-
ious shape slots on the radiator or on the ground [2]–[14], adding
folded parasitic strips or resonators in the vicinity of the radiator
Manuscript received April 26, 2012; revised February 28, 2013; accepted
May 01, 2013. Date of publication May 03, 2013; date of current version July
31, 2013. This work was supported in part by National Nature Science Founda-
tion of China under Grant 61171029.
The authors are with School of Electronic and Information Engineering,
South China University of Technology, Guangzhou, Guangdong 510640, China
(e-mail: qxchu@scut.edu.cn; mao.chunxu@mail.scut.edu.cn).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TAP.2013.2261575
or the feed line [13]–[22]. However, the notched band is usually
generated by using only one resonator and can not offer a sharp
selectivity to meet the requirements of practical applications in
most band-notch UWB antennas. On the other hand, bandwidth
of the notched band is another important parameter in the de-
sign of a band-notched UWB antenna. In [21], the bandwidth
could be adjusted by tuning the widths of the metal plates or the
depths of the insets so as to change the loading capacitance and
inductance of the folded strip. In [22], the bandwidth was con-
trolled by adjusting the coupling between the loaded resonators
on the radiator.
In this paper, a very compact UWB slot antenna with im-
proved band-notched selectivity is proposed. A stepped slot an-
tenna fed by a 50 Ohm micro strip line is adopted to realize
impedance matching characteristics in a wide frequency band
and reduce the size of the antenna. The antenna size is only
. By slitting an open-ended quarter-
wavelength slot and a short-ended half-wavelength ring slot on
the ground near the stepped slot, a second-order notched band
of 5.15–5.85 GHz is achieved. Compared with traditional first-
order notched band, the bandwidth and selectivity of the notched
band is improved. Moreover, the bandwidth of the notched band
can be easily controlled by adjusting the lengths of the slots.
Simulated and measured results demonstrate that the proposed
antenna has a great band-notched characteristic and is suitable
for portable UWB equipment.
II. THE PROPOSED ANTENNAS
A. Slot UWB Antenna
The proposed UWB slot antenna without notched band is
shown in Fig. 1(a) (refer to Antenna-I). It is a stepped slot an-
tenna fed by a 50 Ohm micro strip line on the back. The antenna
is fabricated on FR4_epoxy substrate with dielectric constant
of 4.4 and has the size of . The
stepped slot is adopted to realize multiple matching-points (3.5,
5.5 and 9 GHz, as is depicted in Fig. 1) in the UWB and these
matching-points can be adjusted by tuning the parameters of the
slot and the position of the feed line. By adjusting the stepped
slot, the antenna can achieve a wide impedance matching char-
acteristic (3.2 GHz to above 10.6 GHz). Compared with the
UWB antenna proposed in [8], which has impedance matching
bandwidth of 3.8 to 10.6 GHz, the impedance matching charac-
teristic in the low-frequency is improved. Besides, the overall
size of the antenna is reduced. High Frequency Structure Sim-
ulation (HFSS) software is used for designing and optimizing
process and the final parameters refer to Table I. Fig. 2 shows
the simulated and measured of the Antenna-I. The mea-
sured result has a good agreement with the simulated one.
0018-926X/$31.00 © 2013 IEEE
Authorized licensed use limited to: Birla Institute of Technology & Science. Downloaded on April 27,2020 at 13:59:43 UTC from IEEE Xplore. Restrictions apply.

2. 3962 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 61, NO. 8, AUGUST 2013
Fig. 1. Proposed antennas: (a) Antenna-I, UWB slot antenna without notched
band (b) Antenna-II, UWB slot antenna with notched band.
TABLE I
PARAMETERS OF PROPOSED ANTENNAS (UNIT: mm)
Fig. 2 Simulated and measured of Antenna-I.
B. Implementation of Notched Band
Based on the Antenna-I, an UWB antenna with notched band
of 5.15–5.85 GHz is achieved (refer to Antenna-II) by slitting
an open-ended slot and a short-ended split-ring slot on the an-
tenna as shown in Fig. 1(b). The length of the open-ended slot is
Fig. 3 Simulated and measured of the Antenna-II.
about a quarter-wavelength of the frequency (5.35 GHz), which
is little lower than the center frequency of the notched band,
and the length of the split-ring slot is about a half-wavelength
of the frequency (5.7 GHz), which is little higher than the center
frequency of the notched band. The lengths of the slots can be
calculated approximately by
(1)
(2)
where, is the effective dielectric constant, is the speed
of the light in free space and the and are the resonant
frequencies of open-ended slot and the short-ended split-ring
slot respectively [8]. To cover the WLAN band, in this design,
and are initialized as 5.35 and 5.65 GHz. The simulated
of the Antenna-II is depicted in Fig. 3. It can be observed
that a notched band of 5.15–5.85 GHz with improved selectivity
is obtained. The optimized parameters obtained in Ansoft HFSS
are also shown in the Table I.
Fig. 4 shows the photograph of the Antenna-I and the An-
tenna-II. Both of two antennas are fabricated and measured
using Agilent R3770 vector network analyzer. The measured
of Antenna-II is also depicted in Fig. 3, which shows that
the measured result agrees reasonably well with the simulated
one. The discrepancy between the simulated and measured
results may be caused by the influence of SMA connector and
environment of measurement. It can be observed that a notched
band of 5.15–5.9 GHz is achieved and two transmission poles
are produced at the both sides of the notched band, which
ensure that the notched band with great frequency selectivity.
In order to further understand the mechanism of the notched
band, the current distribution at 5.35 and 5.65 GHz are shown
in Fig. 5. As is depicted in Fig. 5(a), the current mainly flows
along the open-ended slot at 5.35 GHz, while at 5.65 GHz the
current mainly flows along the split-ring slot and open-ended
slot. As a consequence, a notched band of 5.15–5.85 GHz can
be achieved.
The simulated and measured radiation patterns of the An-
tenna-II at 3.5, 6.5 and 9.5 GHz are normalized and plotted in
Authorized licensed use limited to: Birla Institute of Technology & Science. Downloaded on April 27,2020 at 13:59:43 UTC from IEEE Xplore. Restrictions apply.

3. CHU et al.: COMPACT NOTCHED BAND UWB SLOT ANTENNA WITH SHARP SELECTIVITY AND CONTROLLABLE BANDWIDTH 3963
Fig. 4. Photograph of the Antenna-I and the Antenna-II.
Fig. 5. Current distribution of the Antenna-II at different frequencies: (a) 5.35
GHz, (b) 5.65 GHz.
Fig. 6. It is observed that the antenna exhibits quasi omni-direc-
tional pattern in the H-plane (xz plane) and dipole-like pattern
in the E-plane (xy plane). It should be noticed that the radiation
patterns in E-plane become imbalanced as frequency increases.
It is observed the maximum gain of the antenna is different
between the simulated and measured results, which is caused
by the tolerance fabrication and measurement error. The imbal-
anced radiation pattern is attributed to the imbalance of current
distribution at the high frequency.
The simulated and measured antenna gains (in the direction
of negative x-axis) of the Antenna-II are shown in Fig. 7. The
Antenna-II keeps a stable gain in the frequency range of UWB,
but sharply decreases to about 4 dBi at the notched band. The
decrease above 9.5 GHz is probably caused by the deteriora-
tion of the radiation characteristics. Fig. 8 shows the simulated
radiation efficiencies of the Antenna-I and Antenna-II. It is ob-
served that the two antenna exhibits stable and high radiation
Fig. 6. Radiation patterns of the Antenna-II: (a) 3.5 GHz, (b) 6.5 GHz, (c) 9.5
GHz.
Fig. 7. Simulated and measured antenna gains of Antenna-II in the negative
direction.
efficiency (about 90 percent) in the UWB band. But for the An-
tenna-II, the radiation efficiency sharply decreases to about 10
percent at the notched band, which demonstrates that the An-
tenna-II has a good band-notched characteristic.
Authorized licensed use limited to: Birla Institute of Technology & Science. Downloaded on April 27,2020 at 13:59:43 UTC from IEEE Xplore. Restrictions apply.

4. 3964 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 61, NO. 8, AUGUST 2013
Fig. 8. Simulated radiation efficiency of Antenna-I and Antenna-II.
Fig. 9. Antennas for comparison: (a) Antenna-IIa, with a open-ended slot, (b)
Antenna-IIb, with a short-ended split-ring slot, (c) Antenna-II.
III. STUDY OF BAND-NOTCHED CHARACTERISTICS
A. Selectivity of the Notched Band
The selectivity of the notched band is a crucial parameter in
the band-notched UWB antenna design, which should be taken
into consideration in the practical applications. A UWB antenna
with great band-notched selectivity can improve the communi-
cation quality. To evaluate the selectivity of the notched band, a
criterion of roll-off criterion (ROC) is defined, which is the ratio
of the bandwidth of 3 dB to the bandwidth of 10 dB, namely
(3)
where, and are 3 dB and 10 dB band-
width of the notched band, respectively. Fig. 9 shows the three
antennas for studying the relationship between the performance
of the notched band and order of the resonator: (a) Antenna-IIa,
with only an open-ended quarter-wavelength slot; (b) Antenna-
IIb, with only a short-ended half-wavelength ring slot; (c) An-
tenna-II.
Fig. 10 shows the simulated of the three antennas for
comparison. It can be observed that compared with Antenna-II,
the notched bands of Antenna-IIa and Antenna-IIb have a poor
selectivity and bandwidth. For Antenna-II, the two notched
bands produced by the two slot resonators are coupled together
Fig. 10. comparison of the three band-notched antennas.
to shape a single notched band with second-order characteris-
tics, and two transmission poles are produced at the both sides
of the notched band. As a result, a notched band with great
frequency selectivity is achieved. Referred to (3), the ROC
of the Antenna-II can be figured out as 0.65. However, in [8]
and [23], the ROCs of the first-order notched bands are only
about 0.3 and 0.45. Thus, the selectivity and bandwidth of the
second-order notched band are improved greatly compared with
the first-order notched band as expected. In addition, the in
the notched band keeps stable about 2 dB, resulting in most
of the signals in the notched band can be reflected. Therefore, it
can be concluded that the performance of the notched band can
be greatly improved by employing a second-order resonator.
B. Bandwidth Controllability
The bandwidth of notched band is another important param-
eter in the design of band-notched UWB antenna. The control-
lable bandwidth of notched band can meet the requirements of
various wireless communication systems. However, little atten-
tion has been paid to the study of bandwidth controllability. In
this paper, the bandwidth controllability will be taken into con-
sideration.
In the proposed antenna, the notched band is formed by the
open-ended slot and the short-ended split-ring slot which func-
tion as resonators. Therefore, the bandwidth of the notched band
could be controlled by the resonant frequencies of the slots and
coupling between them. Figs. 11 and 12 exhibit the bandwidths
of the notched bands vary with different lengths of the open-
ended slot and the short-ended split-ring slot respectively. It
can be seen that the bandwidth of the notched band broadens
when the open-ended slot increases and the short-ended split-
ring slot decreases, vice versa. Moreover, the selectivity of the
notched band keeps almost unchanged when the bandwidth of
the notched band changes. Fig. 13 illustrates the bandwidth of
the notched band varies with the distance between the open-
ended slot and the short-ended split-ring slot, which reflect the
effect on the bandwidth of coupling between the two resonators.
It can be found that the bandwidth of the notched band increases
as decreases, i.e. the distance becomes large between the
slot resonators.
Authorized licensed use limited to: Birla Institute of Technology & Science. Downloaded on April 27,2020 at 13:59:43 UTC from IEEE Xplore. Restrictions apply.

5. CHU et al.: COMPACT NOTCHED BAND UWB SLOT ANTENNA WITH SHARP SELECTIVITY AND CONTROLLABLE BANDWIDTH 3965
Fig. 11. Bandwidth of the notched band vary with .
Fig. 12. Bandwidth of the notched band vary with .
Fig. 13. Bandwidth of the notched band vary with .
IV. CONCLUSION
In this paper, a very compact UWB slot antenna and a
UWB antenna with improved band-notched characteristics
have been proposed. A bent stepped slot is used to realize a
wide impedance matching bandwidth and reduce the overall
size of the antenna simultaneously. A notched band to cover
the WLAN has been achieved by etching an open-ended
quarter-wavelength slot on the back of the feed line and a
short-ended half-wavelength split-ring slot near the stepped
slot. The selectivity and the bandwidth controllability of the
notched band have also been explored. Simulated and measured
results show that the compact band-notched UWB slot antenna
has great frequency selectivity and bandwidth controllability,
which demonstrate that the proposed antennas are suitable for
portable UWB systems.
REFERENCES
[1] Federal Communications Commission, First Report and Order, Revi-
sion of Part 15 of the Commission’s Rule Regarding Ultra-Wideband
Transmission System FCC 02-48 Apr. 22, 2002.
[2] Y. C. Lin and K. J. Hung, “Compact ultra-wideband rectangular
aperture antenna and band-notched designs,” IEEE Trans. Antennas
Propag., vol. 54, no. 11, pp. 3075–3081, Nov. 2006.
[3] Y. J. Cho, K. H. Kim, D. H. Choi, S. S. Lee, and S. O. Park, “A minia-
ture UWB planar monopole antenna with 5-GHz band-rejection filter
and the time-domain characteristics,” IEEE Trans. Antennas Propag.,
vol. 54, no. 5, pp. 1453–1460, May 2006.
[4] J. Kim, C. S. Cho, and J. W. Lee, “5.2 GHz notched ultra-wideband an-
tenna using slot-type SRR,” Electron. Lett., vol. 42, no. 6, pp. 315–316,
Mar. 2006.
[5] Q. X. Chu and Y. Y. Yang, “A compact ultra wideband antenna with
3.4/5.5 GHz dual band-notched characteristics,” IEEE Trans. Antennas
Propag., vol. 56, no. 12, pp. 3637–3644, Dec. 2008.
[6] Y. Zhang, W. Hong, C. Yu, Z. Q. Kuai, Y. D. Don, and J. Y. Zhou,
“Planar ultra wideband antennas with multiple notched bands based on
etched slots on the patch and/or split ring resonators on the feed line,”
IEEE Trans. Antennas Propag., vol. 56, no. 9, pp. 3063–3068, Sep.
2008.
[7] Y. D. Dong, W. Hong, Q. K. Zhen, and J. X. Chen, “Analysis of planar
ultra wideband antennas with on-ground slot band-notched structures,”
IEEE Trans. Antennas Propag., vol. 57, no. 7, pp. 1886–1893, Jul.
2009.
[8] Z. A. Zheng, Q. X. Chu, and Z. H. Tu, “Compact band-rejected ultra
wideband slot antennas inserting with and resonators,” IEEE
Trans. Antennas Propag., vol. 59, no. 2, pp. 390–397, Feb. 2011.
[9] L. H. Ye and Q. X. Chu, “Improved band notched UWB slot antenna,”
Electron. Lett., vol. 45, no. 25, pp. 1890–1897, Dec. 2009.
[10] W. J. Lui, C. H. Cheng, and H. B. Zhu, “Improved frequency notched
ultra wideband slot antenna using square ring resonator,” IEEE Trans.
Antennas Propag., vol. 55, no. 9, pp. 2445–2450, Sep. 2008.
[11] S. Mohammadi, J. Nourinia, C. Ghobadi, and M. Majidzadeh, “Com-
pact CPW-fed rotated square-shaped patch slot antenna with band-
notched function for UWB applications,” Electron. Lett., vol. 47, no.
24, pp. 1307–1308, Nov. 2011.
[12] Z. L. Zhou, L. Li, and J. S. Hong, “Compact UWB printed monopole
antenna with dual narrow band notches for WiMAX/WLAN bands,”
Electron. Lett., vol. 47, no. 20, pp. 1111–1112, Sep. 2011.
[13] R. Zaker, C. Ghohadi, and J. Nourinia, “Bandwidth enhancement of
novel compact single and dual band-notched printed monopole antenna
with a pair of L-shaped slots,” IEEE Trans. Antennas Propag., vol. 57,
no. 12, pp. 3978–3983, Dec. 2009.
[14] Q. X. Chu and T. G. Huang, “Compact UWB antenna with sharp band-
notched characteristics for lower WLAN band,” Electron. Lett., vol. 47,
no. 15, pp. 838–839, Jul. 2011.
[15] K. H. Kim, Y. J. Cho, S. H. Hwang, and S. O. Park, “Band-notched
UWB planar monopole antenna with two parasitic patches,” Electron.
Lett., vol. 41, no. 14, pp. 783–785, Jul. 2005.
[16] S. J. Wu, C. H. Kang, K. H. Chen, and J. H. Tarng, “Study of an ultra
wideband monopole antenna with a band-notched open-looped res-
onator,” IEEE Trans. Antennas Propag., vol. 58, no. 6, pp. 1890–1897,
Jun. 2010.
[17] K. S. Ryu and A. A. Kishk, “UWB antenna with single or dual band-
notches for lower WLAN band and upper WLAN band,” IEEE Trans.
Antennas Propag., vol. 57, no. 12, pp. 3942–3950, Dec. 2010.
[18] J. R. Kelly, P. S. Hall, and P. Gardner, “Band-notched UWB antenna in-
corporating a micro strip open-loop resonator,” IEEE Trans. Antennas
Propag., vol. 59, no. 8, pp. 3045–3048, Aug. 2010.
[19] L. Li, Z. L. Zhou, and J. S. Hong, “Compact UWB antenna with four
band-notches for UWB applications,” Electron. Lett., vol. 47, no. 22,
pp. 1211–1212, Oct. 2011.
Authorized licensed use limited to: Birla Institute of Technology & Science. Downloaded on April 27,2020 at 13:59:43 UTC from IEEE Xplore. Restrictions apply.

6. 3966 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 61, NO. 8, AUGUST 2013
[20] K. G. Thomas and M. Sreenivasan, “Simple ultra wideband planar
rectangular printed antenna with band dispensation,” IEEE Trans. An-
tennas Propag., vol. 58, no. 1, pp. 27–34, Jan. 2010.
[21] T. G. Ma, R. C. Hua, and C. F. Chou, “Design of a multiresonator
loaded band-rejected ultra wideband planar monopole antenna with
controllable notched bandwidth,” IEEE Trans. Antennas Propag., vol.
56, no. 9, pp. 2875–2883, Sep. 2008.
[22] T. G. Ma and J. W. Tsai, “Band-rejected ultra wideband planar
monopole antenna with high frequency selectivity and controllable
bandwidth using inductively coupled resonator pairs,” IEEE Trans.
Antennas Propag., vol. 58, no. 8, pp. 2747–2752, Aug. 2010.
[23] S. Barbarino and F. Consoli, “UWB circular slot antenna provided with
an inverted-L notch filter for the 5 GHz WLAN band,” Prog. Electro-
magn. Res., vol. 104, pp. 1–13, 2010.
Qing-Xin Chu (M’99–SM’11) received the B.S,
M.E., and Ph.D. degrees in electronic engineering
from Xidian University, Xi’an, Shaanxi, China, in
1982, 1987, and 1994, respectively.
He is currently a Full Professor with the School
of Electronic and Information Engineering, South
China University of Technology, Guangzhou,
Guangdong, China. He is also the Director of the
Research Institute of Antennas and RF Techniques,
South China University of Technology. From Jan-
uary 1982 to January 2004, he was with the School
of Electronic Engineering, Xidian University. From 1997 to 2004, he was a
Professor and later the Vice-Dean with the School of Electronic Engineering,
Xidian University. From July 1995 to September 1998 and July to October
2002, he was a Research Associate and Visiting Professor with the Department
of Electronic Engineering, Chinese University of Hong Kong, respectively.
From February to May 2001 and December 2002 to March 2003, he was a
Research Fellow and Visiting Professor with the Department of Electronic
Engineering, City University of Hong Kong, respectively. From July to October
2004, he visited the School of Electrical and Electronic Engineering, Nanyang
Technological University, Singapore. From January to March 2005, he visited
the Department of Electrical and Electronic Engineering, Okayama University.
From June to July 2008, he was also a Visiting Professor with the Ecole
Polytechnique de I’Universite de Nantes, Nantes, France. He has authored or
coauthored over 300 papers in journals and conferences. His current research
interests include antennas in mobile communication, microwave filters, spatial
power-combining array, and numerical techniques in electromagnetics.
Prof. Chu is a Senior Member of the China Electronic Institute (CEI). He
was the recipient of the Tan Chin Tuan Exchange Fellowship Award, a Japan
Society for Promotion of Science (JSPS) Fellowship, the 2002 and 2008 Top-
Class Science Award of the Education Ministry of China, and the 2003 First-
Class Educational Award of Shaanxi Province.
Chun-Xu Mao was born in Hezhou, Guangxi
Province, China. He received the B. Eng. Degree in
communication engineering from Guilin University
of Electronic and Technology, Guilin, China, in
2010, and is currently working toward the M. E.
degree at South China University of Technology,
Guangzhou.
His research interests include the design and anal-
ysis of UWB antennas.
He Zhu was born in Jinan, Shandong, China. He re-
ceived the B.S. degree in electronic science and tech-
nology from South China University of Technology,
Guangzhou, China, in 2011, and is currently working
toward the M.E. degree at South China University of
Technology, Guangzhou.
His research interests include the design and anal-
ysis of UWB components.
Authorized licensed use limited to: Birla Institute of Technology & Science. Downloaded on April 27,2020 at 13:59:43 UTC from IEEE Xplore. Restrictions apply.