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Small-size planar triangular monopole
antenna for UWB WBAN applications
J.R. Verbiest and G.A.E. Vandenbosch
A novel topology, based on the PTMA, is investigated in view of
UWB WBAN applications. It is shown that adding carefully placed
slots in the antenna offers a lot of advantages. The study presented
treats all aspects that are important. First, the specifications in the
frequency domain are met for the lower UWB band. Secondly, the
design is made such that a small size is obtained. Thirdly, and very
important, the presence of the human body is investigated. Finally,
the pulse distortion in the frequency band 4–7 GHz is investigated
and found to be low. The main conclusion is that this PTMA type is a
very good topology for UWB applications in combination with
human bodies.
Introduction: In the last years ultra -wideband (UWB) te chnology ha s
received much attention in the wir eless world. It is especially suited
for short-range, high-data-rate communication because of the
imposed restrictions on the transmit power. It has already been
shown that UWB technology promises to be a good candidate for
applications in wireles s body area networks (WBAN ) [1].Inthis
Letter, a specific design based on t he planar triangular monopole
antenna (PTMA), to our knowledge for the first time, is investigated
and its suitability for UWB WBAN communication is shown.
w
ptma
w
t
w
m
x
z
y
l
ptma
w
w
c
I
m
I
a
I
feed
I
c
I
gr
I
w
feed
h
g
w
a
Fig. 1 Antenna topology
Design process: In [2, 3 ] a PTMA, based on the Tab monopole [4],is
presented for UWB communication. In [5] a simi lar topology is
presented, however, with coplanar feeding (CPW). The basic topology
as in [2, 3] was selected and a design process was starte d with CST
Microwave Studio [6], aiming at smal l size and large bandwidth, and
using a microstrip feeding approach. To achieve a good VSWR an
innovative topology was conceived, to our knowledge for the first
time, by addin g two sl ots in the ante nna str u cture compared to [2, 3],
one in the radiating element, and one in the g round plane. Fig. 1
shows the final antenna, which has maximum dimensions of 25
28.5 1.27 mm (w l h). All metal parts are simulated as a
perfectly electric conductor (PEC) with a thicknes s t
metal
¼0.017 mm.
The final dimensions are: w
ptma
¼18.76 mm, l
ptma
¼28 mm, w
a
¼
1 mm, l
a
¼18 mm, w
feed
¼2 mm, l
feed
¼8 mm, w
m
¼3 mm, l
m
¼
4 mm, w
t
¼4 mm, w
c
¼4 mm, l
c
¼8mm,andl
gr
¼8 mm. The combi-
nation of the two slots gives a simulated VSWR of less than 2 between
3.25 and 7.55 GHz. This i s shown in Fig. 2,wherethesimulated
VSWR is given for four cases. When no slots are used good
matching is only obtained at two resonance frequencie s: 2.94 and
6.5 GHz. When a slot in the ground plane is added we obtain a
better matching between 2.55 and 7.87 GHz (VSWR < 3.5).
The combination of both slots gives a good matching (VSWR < 2)
between 3.25 and 7.55 GHz. Fig. 3 shows the radiation pattern at
5.5 GHz, which is similar t o that of a monopole-like antenna.
2
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
3
456
789
frequency, GHz
VSWR
w
c
= 0, w
a
= 0
w
c
= 4, w
a
= 1
w
c
= 0, w
a
= 1
w
c
= 4, w
a
= 0
Fig. 2 Simulated VSWR
s no slots
*
slot in ground plane and radiated element
slot only in radiated element
u slot only in ground plane
270
300
330
0
30
0.5
1
60
90
120
150
180
210
240
(+x)
(+y )(+x)(+y )
270
300
330
0
30
0.5
1
60
90
120
150
180
210
240
(+z)
270
300
330
0
30
0.5
1
60
90
120
150
180
210
240
(+z)
Θ, deg Θ, degΦ, deg
Θ
=
90°
Φ
=
0°
Φ
=
90°
Fig. 3 Radiation pattern at 5.5 GHz
Measurements: The antenna was fabri cated on a Rogers RO3210
substrate material with a dielectric constant of 10.2 0.50 at 10 GHz.
The measurements show a VSWR better than 2 for a band between
3.5 and 7.55 GHz, which yields very good ag reemen t wi th t he
calculated results.
2
1
1.5
2
2.5
3
3.5
4
4.5
5
3
456
789
frequency, GHz
VSWR
measured no tissue
measured tissue
simulated no tissue
simulated tissue
Fig. 4 Simulated and measured VSWR with and without biological tissue
Presence of biological tissue: Since the applicat ions in mind involve
the presence of the human body, it is mandatory to study the effect of
the presence of biological tissue. In this Letter, a si mplified model is
used. The antenna is placed on top of a three-layer tissue, dry
skin (e ¼35.36, s ¼3.46 [7], t
dry skin
¼2 mm, r ¼1200 kg=m
3
[8]),
ELECTRONICS LETTERS 11th May 2006 Vol. 42 No. 10
fat (e ¼4.98, s ¼0.27 [7], t
fat
¼ 5 mm, r ¼1000 k g=m
3
[8]), muscle
(e ¼48.88 , s ¼4.61 [7], r ¼1000 kg=m
3
, t
muscle
¼1), with dimen-
sions 60 60 mm in t he x–y-plane. The distance between the bottom
of the antenna and the dry skin layer is 1.5 mm. Fig. 4 shows the
difference in VSWR, both simulated and measured. We obser ve a
small increase in bandwidth, but the matching becomes worse . These
results are very promising.
Pulse distortion: A last but crucial aspect for UWB applications is
the distortion in the time domain of a wideband pulse between two
PTMAs on a human body. This has also been studied using the
simplified tissue model. The distance between the antennas is
200 mm. A wideband pulse, duration 2 ns, pulse shape p (t) [9],is
applied. It has a spectral content P( f )between4and7GHz(Fig. 5).
The output pulse O
with tissue
is compared to the output pulse O
no tissue
.
We observe larger pulse duration in t he presence of tissue (p ulse
duration becomes 2.5 ns), which means that use of this antenna on the
body yields a lower bit rate. The pulse distortion is investigated in the
frequency domain, by studying the pha se of S
21
. No distor tion means
that the phase of S
21
shows linear behaviour, which means that the
derivative wit h frequency is a constant. In the absence of tissue this
derivative is found to be practically a constant: 3.89
. On the human
body there is a variation of the der ivative. It reaches values between
4.58 and 2.77
in the fre quency band targeted. In other words if the
antenna is used in free space there is less distortion and the influence
of the antenna on the pulse is s mall. On t he human body the distortion
becomes larger (46% phase variation compared with free space). It is
important to e mphasise that between 6 and 7 GHz (the region where
VSWR
with tissue
< 2) the variation is smaller (8% phase variation
compared with free space) and the transfer function, S
21
is rela tive
flat. This means t hat this PTMA topology is most suited for use as
UWB antenna between 6 and 7 GHz.
max = max{diff|S
21
[deg]|
with tissue
}
min = max{diff|S
21
[deg]|
with tissue
}
mean = mean{diff|S
21
[deg]|
no tissue
}
diff|S
21
[deg]|=|S
21
[deg](n + 1) – S
21
[deg](n)|
6 to 7 GHz
max
– min
mean
4.58
– 2.77
3.89
100 [%]
=46%
no tissue
with tissue
O
with tissue
, V(×10
4
)
O
n
o
tiss
u
e
, V
with tissue
no tissue
channel
H(f ) = S
21
port 1 port 2
200 mm
0
3
4
5
500 1000
n, MHz
1500 2000 2500 3000
Idiff (S
21
,
deg)I
S
21
,
deg
S
21
,
dB
frequency, GHzfrequency, GHz
4 4.5 5 5.5 6 6.5 7
frequency, GHz
4
–80
–60
–40
–20
4.5 5 5.5 6 6.5 7
-100
0
100
012 34
–2
–2
0
4
0
0.5
1
567
P(t)
p(t), V
ns
012 34
ns
–0.04
–0.02
0
0.02
0.04
0
–1
0
1
0.5 1
ns
1.5 2
Fig. 5 Wideband pulse, p(t), spectral content P(f) of p(t), impulse response
S
21
of channel, phase difference, diff jS
21
[deg]j, and output pulse O
no tissue
and O
with ti ssue
Conclusions: A novel small size PTMA topology has been described.
Wideband behaviour is obtained by adding slots in the antenna
structure. The an tenna has a relative good matching, also in the
presence of the huma n body, and UWB pulse communication on
the human body is pos sible with this antenna .
Acknowledgment: Research financed by a PhD grant of the Institute
for P romotion through Science and Technology in Flanders (IWT
Vlaanderen).
# The Institution of Engineering and Technology 2006
7February2006
Electroni cs Letters online no: 20060377
doi: 10.1049/el:2 0060 377
J.R. Verbiest and G.A .E. Vandenbosch (KULeuven ESAT-TELEMIC,
Kasteelpark Arenberg 1 0, 3001 Leuven, Belgium)
E-mail: joeri.verbiest@esat.kuleuven.be
References
1 Klemm, M., Kovcs, I.Z., Pedersen, G.F., and Tro¨ster, G.: ‘Novel small-
size directional antenna for UWB WBAN=WPAN applications’, IEEE
Trans. Antennas Propag., 2005, 53, (12), pp. 3884–3896
2 Lin, C.C., Kuo, Y.C., and Chuang, H.R.: ‘A planar triangular monopole
antenna for UWB communication’, IEEE Microw. Wirel. Compon. Lett.,
2005, 15, (10), pp. 624–626
3 Chuang, H.R., Lin, C.C., and Kan, Y.C.: ‘A printed UWB triangular
monopole antenna’, Microw. J., 2006, 49,
4 Johnson, J.M., and Rahmat-Samii, Y.: ‘The Tab monopole’, IEEE Trans.
Antennas Propag., 1997, 45, (1), pp. 187–188
5 Chung, W., and Kao, P.-C.: ‘CPW-fed triangular monopole antenna for
ultra-wideband operation’, Microw. Opt. Technol. Lett., 2005, 47,
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6 CST Microwave Studio [online]. Available: http://www.cst.de
7 Internet resource for the calculation of the dielectric properties of the
body tissues in the frequency range 10 Hz–100 GHz [online] http://
niremf.ifac.cnr.it/tissprop/
8 Gowrishankar, T.R., Stewart, D.A., Martin, G.T., and Weaver, C.:
‘Transport lattice models of heat transport in skin with spatially
heterogeneous temperature-dependent perfusion’, Biomed. Eng. Online,
2004, 3,p.42
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pulse design algorithm’, IEEE Commun. Lett., 2003, 7, (5), pp. 219–221
ELECTRONICS LETTERS 11th May 2006 Vol. 42 No. 10
