Low-cost small-size tapered slot antenna for lower band UWB applications

Abstract

A low-cost small-size tapered slot antenna (TSA) is investigated in view of ultra-wideband (UWB) applications. First, the bandwidth of the antenna is studied for the lower UWB band: 3.1-4.85 GHz. Secondly, the design is made as small as possible. Thirdly, the pulse distortion of a modulated Gaussian pulse in the lower UWB band, between 3.5 and 4.5 GHz, is investigated based on the measured S21-parameter. The low distortion observed indicates that this TSA is suitable for applications in the lower UWB band.

Full text

Low-cost small-size tapered slot antenna
for lower band UWB applications
J.R. Verbiest and G.A.E. Vandenbosch
A low-cost small-size tapered slot antenna (TSA) is investigated in
view of ultra-wideband (UWB) applications. First, the bandwidth of
the antenna is studied for the lower UWB band: 3.1–4.85 GHz.
Secondly, the design is made as small as possible. Thirdly, the pulse
distortion of a modulated Gaussian pulse in the lower UWB band,
between 3.5 and 4.5 GHz, is investigated based on the measured
S
21
-parameter. The low distortion observed indicates that this TSA is
suitable for applications in the lower UWB band.
Introduction: In the last few years ultra-wideband (UWB) has
received much attention in the wireless world. It has many (potential)
applications, both low data rate (LDR) and high data rate (HDR), such
as home networking, home electronics, wireless area networks (WAN)
etc. [1]. In this Letter, a dedicated antenna design based on the tapered
slot antenna (TSA) is investigated, to our knowledge for the first time,
and its suitability in the lower UWB band is clearly shown.
Design process: As antenna topology the TSA is chosen. It consists
of a tapered slot etched in the metallisation on top of a dielectric
layer. It is an end-fire antenna, with larger bandwidth than a typical
broadside antenna [2], and is mainly used in millimetre-wave appli-
cations. Our design is based on the classic TSA and fed by a
microstrip line. The design is made as small as possible using
a high dielectric substrate material. This topology was selected and
a design process was started with CST Microwave Studio [3], aiming
atsmallsizeandabandwidth(S
11
10 dB) between 3.1 and
4.85 GHz, the lower band of UWB used by direct sequence UWB
(DS-UWB) applications.
Fig. 1 shows the antenna topology obtained after the design process
followed. It has a maximum dimension of 29.75 23.00 1.27 mm
(w l h
s
). It is fabricated on a Roger RO3210 substrate material with
a dielectric constant e of 10.2 0.50 at 10 GHz. We assume no losses
and a constant permittivity with frequency. All metal parts are simulated
as perfect electric conductors (PECs) with thickness t
metal
¼0.017 mm.
The dimensions are l
feed
¼21.375 mm, w
feed
¼0.5 mm, l
1
¼2.5 mm,
w
1
¼1.4 mm, l
2
¼1 mm, w
2
¼0.5 mm, l
3
¼9 mm, D
1
¼9 mm,
D
2
¼5 mm, D
3
¼6.5 mm. The slot varies according to x ¼ay
b
with
a ¼F=l
b
, b ¼2.9 and F ¼10.
ay
b
z
x
h
s
w
feed
l
1
l
2
l
3
I
feed
w
2
w
1
y
x
w
Δ
1
Δ
3
Δ
2
l
Fig. 1 TSA antenna topology
Simulation and measu rements results: Fig. 2 shows the simulated and
measured return loss against frequency. The simulated S
11
is situated
below 7 dB between 3.01 and 5.69 GHz, the measured one between
3.07 and 5.76 GHz. The simulated S
11
is situated below 10 dB
between 3.18 and 5.62 GHz, the measured one between 3.06 and
5.67 GHz. We observe that the bandwidth lies in the lower UWB band
with good agreement between simulations and measurements.
–50
2.0 2.5 3.0 3.5 4.54.0 5.0 5.5 6.0
simulated
measured
–45
–40
–35
–30
–25
–20
–15
–10
–7
–5
0
frequency, GHz
S
11
, dB
Fig. 2 Si mulated and measured return l oss against frequency normalised
to 50 O
Pulse distortion: A very crucial aspect in UWB communications is
pulse distortion. This is studied in this Letter as follows. First, the
impulse response between two TSAs is measured. The distance d
between the antennas is 600 mm (measured from centre to centre).
The measurements are performed in a typical lab multipath environ-
ment. Secondly, using these results and a simple UWB communica-
tion system (Fig. 3),implementedintheAdvancedDesignSystem
(ADS)ofAgilent[4], the distortion of a modulated Gaussian pulse,
with a spectrum between 3.5 and 4.5 GHz, is studied. Fig. 4 shows the
measured magnitude and the variation of the phase of S
21
,which
represent the impulse response, H( f ), of the antenna system. It is
common knowledge that, in a case where the transfer function is flat
and the phase is linear, the transmitted signal has very little distortion.
We indeed observe a relative flat magnitude and a linear phase.
Gaussian
pulse
g
t
(t )
g
r
(t )
G
r
(f )
output
G
t
(f )
s(t
)
S(f
)
S
21
= H(f )
f
c
f
c
d
Fig. 3 Simple UWB communication setup
–2500
2.0 2.5 3.0 3.5
4.0 4.5
5.0 5.5 6.0
–2000
–1500
–1000
–500
0
frequency, GHz
°
–65
–60
–50
–55
–45
–40
–35
–30
S
21
, dB
a
b
Fig. 4 Measured magnitude and phase of S
21
against frequency normal-
ise d to 50 O
a Magnitude
b Phase
Fig. 5 shows the transmitted Gaussian pulse, g
t
(t), and its spectrum
G
t
( f ). It is modulated on a carrier, f
c
¼4 GHz. In this way a UWB
pulse, s(t), is obtained with a spectrum, S( f ). In the receiver we
ELECTRONICS LETTERS 8th June 2006 Vol. 42 No. 12

demodulate the pulse and pass it through a lowpass filter. In this way the
received Gaussian pulse, g
r
(t), is obtained. We observe that the received
pulse has little distortion in this multipath environment. Based on these
observations we can conclude that the antennas introduce very little
distortion.
0
0
3.0
3.5
4.0
4.5
5.0
0.2
frequency, GHz
frequency, GHz
frequency, GHz
0.4
0.6
0.8
1.0
5
10 15
time, ns
–10
0
–1.0
0.5
–0.5
0
0
0.5
1.0
1.0
10
20
g
r
(t ), mV
G
r
(f ), dBm
S(f
), dBm
G
t
(f ), dBm
s(t
), V
g
r
(t ), V
–200
–200
–150
–100
–50
0
0
–200
–150
–100
–50
0
0.2
0.4 0.6
0.8
1.0
–140
–80
–30
Fig. 5 Gaussian pulse at transmitter, g
t
(t), and its spectrum, G
t
(f) (top
diagrams); modulated Gaussian pulse, s(t), and its spectrum S( f ) (middle
diagrams); received Gaussian pulse, g
r
(t), and its spectrum G
r
( f ) (bottom
diagrams)
Conclusions: A TSA has been investigated with a view to UWB
applications. We observe a good matching (S
11
10 dB) in the
lower UWB band. The pulse distortion of a modulated Gaussian pulse
between 3.5 and 4.5 GHz has been investigated, and found to be
small. We conclude that the designed TSA is a suitable low-cost
small-sized UWB antenna for application in the lower UWB band
between 3.1 and 4.85 GHz, a band for use in DS-UWB.
Acknowledgment: Research financed by a PhD grant of the Institute
for Promotion through Science and Technology in Flanders (IWT
Vlaanderen).
# The Institution of Engineering and Technology 2006
28 April 2 006
Electroni cs Lett ers online no: 20061333
doi: 10.1049/el:20061333
J.R. Verbiest and G.A.E. Vandenbosch (KULe uven ESAT-TELEMIC,
Kasteelpark Arenberg 10, 3001 Leuven, Belgium)
E-mail: joeri.verbiest@esat.kuleuven.be
References
1 Allen, B., Brown, T., Schwieger, K., Zimmerman, E., Malik, W.,
Edwards, D., Ouvry, L., and Oppermann, I.: ‘Ultra wideband:
applications, technology and future perspectives’. Int. Workshop on
Convergent Technologies (IWCT), 2005
2 Yngvesson, K.S., Korzeniowski, T.L., Kim, Y.-S., Kollberg, E.L., and
Johnsson, J.F.: ‘The tapered slot antenna – a new integrated element for
millimeter-wave applications’, IEEE Trans. Microw. Theory Tech., 1989,
37, pp. 365–374
3 CST Microwave Studio, [Online]. http://www.cst.de
4 Advanced Design System, [Online]. http://eesoft.tm.agilent.com
ELECTRONICS LETTERS 8th June 2006 Vol. 42 No. 12