World Journal of Engineering and Technology, 2013, 1, 17-22
http://dx.doi.org/10.4236/wjet.2013.12003 Published Online August 2013 (http://www.scirp.org/journal/wjet)
Design and Simulation by HFSS of a Slim UWB PIFA
Antenna
Abdelhakim Elouadih1, Ahmed Oulad-Said2, Moha Mrabet Hassani1
1Department of Physics, Semlalia University of Sciences (FSSM), Marrakesh, Morocco; 2Department of Electrical and Telecommu-
nications Engineering, Royal Air Academy (ERA), Marrakesh, Morocco.
Received April 7th, 2013; revised May 16th, 2013; accepted July 5th, 2013
Copyright © 2013 Abdelhakim Elouadih et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
This paper describes the design and simulation by High Frequency Structure Simulator (HFSS) of a probe-fed Planar
Inverted-F Antenna (PIFA) for the Ultra Wide Band (UWB) personal area networks. The slim antenna presents a height
of 2 mm and a bandwidth of more than 766 MHz. This bandwidth was improved by etching a U-slot in the antenna
patch. The bandwidth offered then by the antenna is 839 MHz around the resonant frequency of 9 GHz. The improve-
ment of bandwidth was accompanied by decreasing in gain and radiation efficiency. The simulation allowed the char-
acterization of the designed antenna and the computing of different antenna parameters like S11 parameter, resonant
frequency, bandwidth, radiation efficiency, gain and diagram pattern. The results are very interesting and respect the
Federal Communications Commission (FCC) requirements.
Keywords: PIFA; HFSS; UWB
1. Introduction
UWB is a communication method used in wireless net-
working to achieve high bandwidth connections with low
power utilization. Originally designed for commercial
radar systems, UWB technology has potential applica-
tions in consumer electronics and Wireless Personal Area
Networks (PAN). Ultra-wide band wireless radios send
short signal pulses over a broad spectrum. The wide sig-
nal allows UWB to commonly support high wireless data
rates of 480 Mbps up to 1.6 Gbps at distances up to a few
meters. It’s the next generation Bluetooth [1]. The use of
such technology is increasing and it requires antennas
that should have broad working bands. For this, the au-
thor tried by this paper to design an antenna for UWB
use that should respect the requirements of the American
telecommunications regulator FCC. The designed an-
tenna can be mounted on very slim mobile or handset
devices giving the antenna thickness equal to 2 mm.
2. UWB Requirements
Before Ultra-wideband refers to radio technology with a
bandwidth exceeding the lesser of 500 MHz or 20% of
the arithmetic center frequency (called also fractional
bandwidth) according to FCC. The FCC authorized the
unlicensed use of UWB in the frequency range from 3.1
to 10.6 GHz. The FCC power spectral density emission
limit for UWB transmitters is −41.3 dBm/MHz. However,
the emission limit for UWB emitters may be significantly
lower (as low as −75 dBm/MHz) in other segments of the
spectrum [2].
3. Antenna Description
The designed antenna has a PIFA configuration. The
PIFA consists in general of a ground plane, a top plate
element, a feed wire attached between the ground plane
and the top plate, and a shorting wire or strip that is con-
nected between the ground plane and the top plate. The
antenna is fed at the base of the feed wire at the point
where the wire connects to the ground plane. The PIFA is
an attractive antenna for wireless systems where the
space volume of the antenna for wireless systems where
the space volume of the antenna is quite limited. It re-
quires simple manufacturing, since the radiator must only
be printed. The addition of a shorting strip allows good
impedance match to be achieved with a top plate that is
typically less than λ/4 long. The resulting PIFA is more
compact than a conventional half-wavelength probe-fed
patch antenna [3]. As shown in Figures 1 to 3, the

Design and Simulation by HFSS of a Slim UWB PIFA Antenna 18
designed antenna has a rectangular radiating patch which
the length L is equal to 30 mm and the width W equal to
40 mm. The patch is placed at a height h equal to 2 mm
from the ground plan. The ground plan has the same di-
mensions as the antenna. The patch is matched to the
ground plan via a rectangular shorting plate which the
width Ws is equal to 1 mm and has the same height h.
The shorting post of usual PIFA types is a good method
for reducing the antenna size, but results in narrow im-
pedance bandwidth. It is placed in the (yz) plan at a dis-
tance D equal to 19.5 mm from the edge center. The
feeding point is situated at a distance p equal to 1 mm
from the rear edge of the patch. The patch is fed by a 50
Ω wire, a semi-rigid coax with centre conductor that ex-
tends beyond the end of the outer conductor is used to
form the PIFA feed wire. The outer conductor of the
coax is soldered to the edge of a small hole drilled in the
ground plane at the feed point. The volume between the
radiating plate and the ground plan is filled by the FR4_
epoxy substrate S (εr = 4.4, tgδ = 0.02).
4. Reflection Coefficient
As given by the HFSS simulator (It uses the finite ele-
ment model FEM) and shown in Figure 4, the designed
antenna presents (along the UWB spectrum band from
3.1 to 10.6 GHz) 2 peaks. The first one is around 7 GHz,
the second is around 8.8 GHz. For more precision, a re-
finement sweep is done around the second peak. The
result is presented in Figure 5. We can see a −10 dB
bandwidth of 766 MHz (from 8545 to 9311 MHz). It’s a
width greater than the 500 MHz required by the FCC and
it is compliant to work in FCC band 11 and 12 of the
group 4 of UWB allocated bands.
5. Bandwith Improvement
Even the found bandwidth respects FCC requirements,
the author tried to increase the bandwidth of this antenna
without increasing the volume or the height to respect a
slim shape. For this, a U-slot was etched on the antenna
patch around the feeding point. The Figure 6 and Table
1 give its position and dimensions. The simulation result
is shown by Figure 7.
We can also see both peaks. We can notify that the S11
of the first peak is reduced to better values. But the in-
teresting improvement is for the second band. The new
Figure 1. Perspective view of the antenna.
Figure 2. Top view of the antenna.
Figure 3. Side view of the antenna.
3100 Freq [MHz]
S
11
[db]
4600 610076009100 10600
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
7200 MHz
8842 MHz
Figure 4. S11 (frequency) in the UWB band.

Design and Simulation by HFSS of a Slim UWB PIFA Antenna 19
Fr
eq
[
MHz
]
S
11
[dB]
-25.00
-20.00
-15.00
-10.00
8545 8698 8851 90059158 9311
Figure 5. S11 according to frequency in the 8.8 GHz band.
Figure 6. The slot dimensions.
Table 1. The slot dimensions values.
J1 10 mm J4 8 mm
J2 4 mm J5 1 mm
J3 3 mm J6 1 mm
−10 dB bandwidth as shown in Figure 7 is equal to 839
MHz (from 8534 to 9373 MHz). The band increased by
73 MHz (10%). The fractional bandwidth increased from
0.08 to 0.09.
6. Simulation Results
6.1. The VSWR in the 8.8 GHz Band
The Figure 8 shows a VSWR min equal to 1.16. The
maximum is 1.93. The whole band presents then a 1.66:1
VSWR bandwidth. The VSWR values are then very in-
teresting.
6.2. The Antenna Parameters
The Figure 9 summarizes the mean antenna parameters
for the selected band as peak directivity, peak gain and
radiation efficiency. The antenna presents good values
for these parameters especially the gain and the radiation
efficiency. We can see from the figure that the value of
gain (9.79 dBi), directivity (11.25%) are so high as well
as the radiation efficiency (87%).
6.3. Radiation Pattern
The Figures 10 and 11 present respectively the 2D radia-
tion pattern (for the maximum total field) and the 3D
radiation pattern. As the pattern shape is concerned. The
antenna has no privileged antenna direction even if the
field intensity is weak in around phi = ±9˚. The maxi-
mum field is for theta = 30˚. The field maximum inten-
sity becomes greater around phi = ±180˚. The total field
intensity reaches 23.94 V/m. The 3D radiation pattern
shows no secondary lobes and practically no rear radia-
tion .that is interesting to prevent human use from radi-
ating high frequencies waves.
7. Discussion
A slim UWB PIFA antenna is then designed with very
compliant values of the bandwidth, the gain, the radiation
efficiency with a thickness equal to 2 mm. The band-
width was broaden and increased by 10%. This im-
provement couldn’t be done without influencing other
antenna parameters as gain and radiation efficiency. If
we compare the new values of antenna parameters after
etching slot to whom found before slotting the patch as
shown in Figure 12, the gain and directivity lost respec-
tively 0.7 dBi and 0.3 dBi. The radiation efficiency de-
creases from 100% to 87%. Beside this decrease of pa-
rameters, the requirements are yet respected and we have
margin to improve more and more bandwidth viewing a

Design and Simulation by HFSS of a Slim UWB PIFA Antenna 20
Freq [MHz]
S
11
[dB]
-25.00
-20.00
-15.00
-10.00
8534 8702 8870 9037 9205 9373
Figure 7. S11 according to frequency in the 8.8 GHz band (with slotted patch).
Freq [MHz]
VSWR
1.00
8534
8702 8870 90379205 9373
1.40
1.60
1.80
2.00
1.20
Figure 8. VSWR according to frequency in the 8.8 GHz band.
Figure 9. The antenna parameters as given by simulation.

Design and Simulation by HFSS of a Slim UWB PIFA Antenna 21
6.14
24.0 24.0
-150
-90
-60
0
30
60
90
120
150
-180
18.05
22.02
10.11
14.08
-30
4.2
-120
Figure 10. 2D radiation pattern for E-Field (for theta = 30˚).
rETotal [Y]
2.3946e + 001
2.2467e + 001
2.0987e + 001
1.8028e + 001
1.9507e + 001
1.6548e + 001
1.5068e + 001
1.3588e + 001
1.2109e + 001
1.0629e + 001
9.1494e + 000
7.6697e + 000
6.1900e + 000
4.7103e + 000
3.2306e + 000
1.7509e + 000
2.7122e - 001
Z
Theta
Ph1 Y
Figure 11. The 3D radiation pattern.

Design and Simulation by HFSS of a Slim UWB PIFA Antenna 22
Figure 12. The antenna parameters before slotting the patch.
this interest of our application. In comparison with
precedent works [4-12] that have the same goal design-
ing UWB for different band groups, the designed antenna
presents a bandwidth litter but a very high gain and ra-
diation efficiency.
8. Conclusion
In this paper, a slim antenna was designed for the UWB
application with a band of 839 MHz around 8.8 GHz.
The antenna parameters are very compliant for this ap-
plication. The bandwidth was improved with a tolerable
degradation in some of antenna parameters. The designed
antenna presents very significant values of gain and ra-
diation efficiency and could be a very compliant solution
for the applications that need gain and directivity such
locating and tracking application (anti-collision vehicle
radar or imaging radar). The most important application
of the ultarwideband is the data transmission using
spread spectrum allowing high data speed without inter-
fering with conventional narrowband and carrier wave
used in the same frequency band. The designed antenna
can be used in different applications and it is then a suc-
ceeded trade-off that respects the FCC UWB require-
ments.
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