Design of a Compact UWB Planar Antenna with Band-Notch Characterization

Abstract

A compact ultra-wideband (UWB) antenna with band-notch characteristic of size 28 mm times 29 mm is proposed. This antenna is designed to cover the Federal Communication Commission (FCC) bandwidth for UWB applications (3.1-10.6 GHz) and have a notch- filtering at the IEEE 802.1 Ia frequency band (5.15-5.825 GHz). This notch-filter effect is obtained by introducing a resonant U-shaped slot at this frequency. The design parameters and the performance of the proposed antenna are analyzed by using different techniques to assure the validity of the simulated results. Comparison between measurements and simulation is also presented.

Full text

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Design of a Compact UWB Planar Antenna with Band-Notch
Characterization

Hany M. Zamel*, Ahmed M. Attiya* and Essam A. Hashish**
* Electronics Research Institute – Microwave Engineering Dept.
** Faculty of Engineering – Cairo University
e-mail: Hany_Mahmoud@eri.sci.eg

Abstract


28
Commission (FCC) bandwidth for UWB applications (3.1–10.6 GHz) and have a notch-
filtering at the IEEE 802.11a frequency band (5.15–5.825 GHz). This notch-filter effect is
obtained by introducing a resonant U-shaped slot at this frequency. The design parameters
and the performance of the proposed antenna are analyzed by using different techniques to
assure the validity of the simulated results. Comparison between measurements and
simulation is also presented

Key words :Ultra-wideband (UWB) antenna; band-notched UWB antenna; transient analysis.


I. Introduction

Recently, UWB communication systems operating in the frequency range from 3.1 to 10.6 GHz has
been released by the Federal Communication Commission (FCC) [1]. UWB communication antennas require
low standing wave ratio (SWR<2), constant phase center, constant group delay and constant gain over entire
operating frequency band [2]. In addition to these requirements, it is also required to use antennas of small size
to reduce the total size and weight of the communication equipments. Printed monopole antennas can be
considered as a good candidate for UWB applications [3] due to their light weight, simple structure and ease of
mass production. However, existing Wireless Local Area Network (WLAN) and IEEE 802.11a systems
operating in the frequency band (5.150 – 5.875 GHz) can cause interference with UWB systems. Therefore, a
band stop filter in this band would be required to reduce the inference between UWB systems and these systems.
To avoid adding new circuits to the communication system, band-notching technique can be applied directly to
various UWB planar antennas by loading the UWB antenna with a resonant slot at the center frequency of the
stop band. Different configurations of this slot are introduced for this purpose such as U-shape, V-shape and I-
shape [4] -[9] These configurations are based on adding the slot on the radiating patch. However, Su and Wong,
[10], introduced another technique by adding these slots on the ground plane of the antenna structure.

In this paper, a new compact UWB patch antenna with a band-notching is presented. The band-
notching is obtained by embedding nearly half-wavelength inverted U-shaped slot in the radiating patch. Low et
al. [11] introduced two wide slots and partial ground plane to increase the bandwidth of the antenna. In the
present design, these two wide slots, that are used to increase the operating bandwidth, are replaced by a strip of
smaller width at the top of the antenna structure. Then a narrow slot of U-shape is added to the patch to
introduce the band-notching effect. The design parameters for achieving optimal performance are investigated
by using the transmission-line model [12]. Section II presents the details of the antenna structure and the design
procedure. Full wave analysis of the proposed antenna in frequency domain is obtained by using ANSOFT
HFSS ® which is based on finite element analysis. On the other hand, pulse radiation characteristics of the
proposed antenna are obtained directly in time domain by using XFDTD ® which is based on finite difference
time domain. Comparison between the different numerical techniques and experimental results are presented in
Section III.
A compact ultra-wideband (UWB) antenna with band-notch characteristic of size
mmmm 29
×
is proposed. This antenna is designed to cover the Federal Communication
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II. Antenna Structure and Design

Figure 1 shows the geometry of the proposed antenna, with an inverted U-slot on the radiating patch
.The patch has the form of a rectangle with a step at its upper end. Tapered section is used to connect the
rectangular patch to the feed line. This tapering is used to improve the matching of the antenna over the
operating bandwidth. A partial ground plane having the length of the feeding line is used on the other side of the
substrate. The total size of the antenna is
mmmm 29 28
×
r ε = 4.7 is used.
The resonant length of a microstrip patch can be obtained by using simple relations of the effective
relative dielectric constant as a function of the substrate parameters and the operating frequency [12]. However,
in the present case, the patch does not have a ground plane on the other side of the substrate as shown in Fig.1.
Thus, it would be required to modify the equation of the effective dielectric constant in this case. It would be
assumed that this equation has the same form of the corresponding equation of the microstrip structure with a
different multiplication coefficient for the term
Wh/
as follows [12]
1
+=
reff
ε
. An FR4 substrate of thickness h =1.574 mm and
2/1
1
2
1
2
−



+
−+
W
h
A
rr
εε
(1)
where A is the new multiplication coefficient. The remaining equations used to design a patch antenna are
assumed to be the same as follows:
c
W
1
2
+
2
=
r
f
ε
(2)
(3)
reff
eff
f
c
L
ε
2
=

(4)
LLL
eff
∆−=
2
(5)
hL5 .0
=∆


where c is the speed of light in free space, L and W are the length and the width of the resonant patch antenna
respectively. By simulating different patches with different substrate parameters, it could be possible to obtain
the appropriate value of the multiplication coefficient A. It is found that the value of this coefficient that
optimally fits the simulated results would be 11.25.
In the present design, the operating frequency f is assumed to be the center frequency of the UWB
range at 5.7 GHz. For this operating frequency and substrate parameters which are discussed before, the
dimensions of the patch would be W =15.6mm and L =13mm. These dimensions represent the starting point
for the present design of the UWB shown in Fig. 1.
Two modifications are introduced on this patch to improve its operating bandwidth. The first one is to
taper the patch near the feeding microstrip line. The second modification is to remove two notches on the upper
corners of the patch. However, due to the tapering effect of that part connected to the microstrip line, the
dimensions of the patch should be modified to be matched with the line such that the length L is changed to be
13.5mm and the width W is changed to be 15mm. Using these dimensions with tapering length
are found to be quite adequate to introduce an UWB patch antenna that can be tuned to operate in the frequency
range from 3.80 to 12.0 GHz as it is shown in the results at the following sections.
To obtain the band rejection characteristic, an inverted U-slot is inserted in the radiating patch as
shown in Fig.1. The total slot length
slot
L
is found to be approximately 0.45
wlwL
2
−+=
λ
is the slot wavelength at the center frequency of the rejected band. This slight difference from
half wavelength can be explained due to the fringing effect of the field at the ends of the slot. The effective
wavelength of the slot is given by [13]
λλ
=
mm5 . 1
2=
L

eff
λ
of the slot as follows
sloteffssssslot
w
_21
45. 0
λ=−
(6)
where
sloteff _
sloteffsloteff_0_
/ ε
(7)

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where
slot eff _
ε
is the effective dielectric constant of the narrow slot structure
2
1
_
+
=
r
sloteff
ε
ε
(8)
This slot corresponds to a nearly half-wavelength resonator at the center frequency of the required stop-band.
This resonator would introduce high reflection at its resonance frequency which corresponds to the operation of
a band-rejection filtering effect. Thus, as a first order of approximation, the required slot length to obtain the
notch frequency is given by:
sloteff notch
slot
f
c
L
_
45
ε
. 0
=
(9)
This value is used as a starting point for optimizing the slot length to obtain exactly the required band-rejection.
To add another degree of freedom in the design of the U-slot, it is assumed that its arms have different width
with respect to its base as shown in Fig. 1. Thus, the optimization parameters in this case would be the four
parameters (
2
,,
ssss
wwlw
). It is found that the slot length has a greater impact on the band-rejection than the
slot width. Therefore, the two parameters
rejection.


III. Results and Discussions

Frequency domain simulation of the proposed antenna is obtained by using High Frequency Structure
Simulation (ANSOFT HFSS) ®, which is based on finite element technique for electromagnetic boundary value
problem. The simulations have shown that the performance of the proposed antenna is critically dependent on
the tapering length
standing wave ratio (VSWR) of the proposed antenna without slot is shown in Fig. 2. This figure shows that the
bandwidth of the simulated patch antenna is in the frequency range from 3.7 to 13.65 GHz, which covers the
bandwidth of the FCC definition for UWB indoor communication systems.
After adding the inverted U-slot inside the patch, most current flows back to the feeding microstrip line
and degrade radiation in the frequency band from 5 GHz to 6 GHz. Figure 3 shows a comparison between the
measured and simulated voltage standing wave ratio (VSWR) with the inverted U-slot. It can be noted that this
antenna has a band-notching effect in the frequency range from 5.1 to 6.2 GHz. Figure 4 shows how this slot
length can be used to design other stop-bands.
Figure 5 shows the max antenna gain at
0
=θ
without the slot. The result shows that the two antennas have good and very similar antenna gains, except that
the slotted antenna has a sharp antenna gain decrease in the notched frequency band 5.35 to 6.2 GHz.
The time domain response of the patch antenna is another important criterion to determine the
performance of the UWB antenna. UWB antenna should be able to transmit the UWB pulse with minimum
ringing effect since this ringing effect would reduce the channel capacity. To show the efficiency of the
proposed antenna for producing sharp pulsed signal, the response due to a Gaussian pulse is studied. The input
Gaussian pulse is defined as
)(tV
=
where σ is a factor which is inversely proportional to the spectral bandwidth of such Gaussian pulse. In the
present case the value of σ is assumed to 50ps which corresponds to a
Figure 6 shows the radiated field in the E-plane (y-z plane) of the proposed antenna without the notch
filter slot at different angles. of θ These results show that the radiated field is nearly the second derivative of
the input signal. It can be noticed the high fidelity of this antenna such that the shape of the radiated pulse is
slightly dependent on the direction of propagation. It can also be noted that the radiated pulse in this case has a
negligible ringing effect which makes this antenna quite suitable for UWB systems. Figure 7 shows the same
results for the patch with the notch filter slot. It can be noticed that the main pulse is nearly same in the two
cases. However, the notch filter slot introduce more ringing effect in this case.
Thus, it can be concluded that a compromise between the ringing effect and the interference with
exciting narrow band systems represents a main challenge in designing an antenna for UWB applications.
1,
s w and sl are the most significant factors to design the required band
2 L , cut region on the upper patch and the length of the ground plane
1L . The voltage
from 3 to 15 GHz for the proposed antenna with and
2
)/(
σ
t
e
−
(10)
dB10
−
bandwidth of nearly 12 GHz.
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IV Conclusions

A new band-notched UWB patch antenna has been proposed and implemented. The frequency-notch
function is obtained by adding a U-shape slot in the radiating patch. By adjusting the length of the slot, the
proposed antenna shows appropriate UWB performance and band notching suitable to avoid interference with
WLAN and IEEE 802.11a. This antenna provides low VSWR in the frequency band from 3.80 to 12.0 GHz with
a band-notching effect at the frequency band from 5.1 to 6.2 GHz. This antenna has also good pulse response at
the far field region. Numerical and experimental results show that this antenna could be a good candidate for
impulse UWB applications.


References

[1] New Public Safety Applications and Broadband Internet Access Among Uses Envisioned by FCC
Authorization of Ultra-Wideband Technology-FCC News Release 2002.
[2] X.H.Wu, Z.N. Chen, M.Y.W. Chia, "Note on Antenna Design in UWB Wireless Communication Systems"
IEEE Conference on Ultra Wideband Systems and Technologies, pp. 503-507, 16-19 Nov 2003.
[3]Seong-Youp Suh, Warren L. Stutzman, and William A. Davis,"A New Ultrawideband Printed Monopole
Antenna: The Planar Inverted Cone Antenna (PICA)", IEEE Transactions on Antennas and Propagation , Vol.
52,No.5, pp. 1361 – 1364, May 2004
[4] S.W. Su, K.L. Wong, and C.L. Tang, "Band-notched ultra-wideband planar-monopole antenna", Microwave
Opt Technol Lett., Vol. 44,pp. 217–219, 2005.
[5] K.L. Wong, Y.W. Chi, C.M. Su, and F.S. Chang,"Band-notched ultra-wideband circular-disk monopole
antenna with an arc-shaped slot", Microwave Opt Technol Lett., Vol. 45, pp. 188–191, 2005.
[6] Y. Kim and D.H. Kwon,"CPW-fed planar ultra wideband antenna having a frequency band notch function",
Electron Lett., Vol. 40, pp. 403–405, 2004.
[7] Y. Kim and D.H. Kwon,"Planar ultra wide band slot antenna with frequency band notch function" IEEE
Antennas Propagat Soc. Int. Symp., Monterey, CA, pp. 1788–1791, 2004.
[8] H. Yoon, H. Kim, K. Chang, Y.J. Yoon, and Y.H. Kim,"A study on the UWB antenna with band-rejection
characteristic", IEEE Antennas Propagation Soc. Int. Symp., Monterey, CA, pp. 1784–1787, 2004.
[9] I.J. Yoon, H. Kim, H.K. Yoon, Y.J. Yoon, and Y.H. Kim,"Ultra-wideband tapered slot antenna with band
cutoff characteristic", Electron Lett., Vol. 41, pp. 629–630, 2005.
[10] Saou-Wen and Kin-Lu Wong,"Printed band-notched Ultra-Wideband quasi-dipole antenna", Microwave
Opt. Technol. Lett., Vol. 48, pp. 418–420, 2006.
[11] Z. N. Low, J. H. Cheong and C. L. Law, "Low-cost PCB Antenna for UWB Application", IEEE Antennas
and Wireless Propagation Letters, Vol. 4,pp. 237-239, 2005.
[12] C. Balanis, Antenna Theory; Analysis and Design, second edition, Wiley and Sons, New York, 1982.
[13] K. C. Gupta, Ramesh Garg, Inder Bahl and Prakash Bhartia , Microstrip Lines and Slotlines , second
edition., Artech house, 1996.

















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Fig. 1 Geometry of the proposed antenna

2 L = 1.5mm,
=0.5 mm ,
=
p
L
1L = 11.5mm,
1 s w =1mm,
3 L = 1.5mm,
4 L = 1.5mm, d = 6.5mm,
mm,
28
=
p
W
mm,
5 . 7
mm.
s w =9mm, sl =3.5mm
mm,
15
=
W
,
2s w
1 w = 3mm;
29
=
5 . 13
=
L
mm and
dl


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Fig. 2 VSWR of the patch antenna without a slot




Fig. 3 Measured and simulated voltage standing wave ratio (VSWR) of the slotted-patch antenna. The total
length of the slot
slot
L
= 3.5 mm

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Fig. 4 Band-notching effect as a function of the slot length
slot
L
.




Fig. 5 Antenna gain of the proposed antenna with and without the slot.

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Fig. 6 Electric field time domain response of the printed monopole antenna without the notch filter slot at
o
90φ =
and for different values of θ



Fig. 7 Electric field time domain response of the printed monopole antenna with the notch filter slot at
and for different values of θ

o
90φ =

E_theta phi=90 theta=0
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
E_theta phi=90 theta=30
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
E_theta phi=90 theta=60
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
E_theta phi=90 theta=90
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
0
30
60
90
y
z
E_theta phi=90 theta=0
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
E_theta phi=90 theta=30
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
E_theta phi=90 theta=60
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
E_theta phi=90 theta=90
-0.2
-0.1
0.0
0.1
0.2
0.3
0.E+002.E-094.E-09
90
60
30
0
y
z
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