Ultra Wideband Part 13 pptx

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Ultra Wideband 354
Fig. 10. Comparison between Simulated and Measured VSWR Curves of the CPW-fed PMEM
Antenna
The previous proposed PMEM antenna can also fed by coplanar waveguide (CPW), in view
of UWB applications. Figure 9 illustrates the conﬁguration of the proposed CPW
−fed PMEM
antenna (Abed, 2008) with the optimal parameters, where an FR4 substrate with relative per-
mittivity of 4.32 and thickness of 1.58mm is used.
The CPW
−fed PMEM antenna with the optimal geometrical parameters was fabricated. Mea-
sured and simulated VSWR (Voltage Standing Wave Ratio) are shown in ﬁgure 10. The mea-
sured bandwidth deﬁned by VSWR
≤ 2 of the proposed antenna with a feed gap of 0.3mm is
from 3GHz to 11.3GHz, which covers the entire UWB band.
The far
−ﬁeld (2D) radiation patterns for the proposed CPW−PMEM antenna are also car-
ried out at three frequencies. Figures
(11.a) and (11.b) show the radiation pattern at azimuthal
and elevation planes, respectively. As it can be seen from the ﬁgures, omnidirectional patterns
can be observed for the H
−plane. These patterns are comparable to those reported for a con-
ventional dipole antenna. It is very important to note that at the higher frequency there is an
obvious deviation from the omnidirectional shape in the H
−plane radiation patterns. Also,
the E
−plane patterns have large back lobes at low frequency and with increasing frequency
they become smaller, splitting into many minor ones. For the antenna gain, it is found that
the proposed microstrip
−fed PMEM antenna has a simulated maximum gain which varies
between 0.18 dBi and 3.61 dBi within the UWB band.

By comparison with the microstrip
−fed PMEM antenna, the CPW−fed PMEM antenna
presents a less gain inside the UWB band with a peak gain of 2.98 dBi at the frequency 5.6
GHz.
-40
-30
-20
-10
0˚
30˚
60˚
90˚
120˚
150˚
180˚
210˚
240˚
270˚
300˚
330˚
-40
-30
-20
-10
Azimuthal pattern (H-plane)
f=3.7 GHz
f=5.7 GHz
f=9.7 GHz
(a)
-40

-30
-20
-10
0
0˚
30˚
60˚
90˚
120˚
150˚
180˚
210˚
240˚
270˚
300˚
330˚
-40
-30
-20
-10
0
f=3.7 GHz
f=5.7 GHz
f=9.7 GHz
Elevation pattern (E-plane)
(b)
Fig. 11. Radiation Pattern of the CPW-fed PMEM Antenna. (a) Azimuthal Pattern (H-plane), (b)
Elevation Pattern (E-plane)
Design and characterization of microstrip UWB antennas 355
Fig. 10. Comparison between Simulated and Measured VSWR Curves of the CPW-fed PMEM

Antenna
The previous proposed PMEM antenna can also fed by coplanar waveguide (CPW), in view
of UWB applications. Figure 9 illustrates the conﬁguration of the proposed CPW
−fed PMEM
antenna (Abed, 2008) with the optimal parameters, where an FR4 substrate with relative per-
mittivity of 4.32 and thickness of 1.58mm is used.
The CPW
−fed PMEM antenna with the optimal geometrical parameters was fabricated. Mea-
sured and simulated VSWR (Voltage Standing Wave Ratio) are shown in ﬁgure 10. The mea-
sured bandwidth deﬁned by VSWR
≤ 2 of the proposed antenna with a feed gap of 0.3mm is
from 3GHz to 11.3GHz, which covers the entire UWB band.
The far
−ﬁeld (2D) radiation patterns for the proposed CPW−PMEM antenna are also car-
ried out at three frequencies. Figures
(11.a) and (11.b) show the radiation pattern at azimuthal
and elevation planes, respectively. As it can be seen from the ﬁgures, omnidirectional patterns
can be observed for the H
−plane. These patterns are comparable to those reported for a con-
ventional dipole antenna. It is very important to note that at the higher frequency there is an
obvious deviation from the omnidirectional shape in the H
−plane radiation patterns. Also,
the E
−plane patterns have large back lobes at low frequency and with increasing frequency
they become smaller, splitting into many minor ones. For the antenna gain, it is found that
the proposed microstrip
−fed PMEM antenna has a simulated maximum gain which varies
between 0.18 dBi and 3.61 dBi within the UWB band.
By comparison with the microstrip
−fed PMEM antenna, the CPW−fed PMEM antenna

presents a less gain inside the UWB band with a peak gain of 2.98 dBi at the frequency 5.6
GHz.
-40
-30
-20
-10
0˚
30˚
60˚
90˚
120˚
150˚
180˚
210˚
240˚
270˚
300˚
330˚
-40
-30
-20
-10
Azimuthal pattern (H-plane)
f=3.7 GHz
f=5.7 GHz
f=9.7 GHz
(a)
-40
-30
-20

-10
0
0˚
30˚
60˚
90˚
120˚
150˚
180˚
210˚
240˚
270˚
300˚
330˚
-40
-30
-20
-10
0
f=3.7 GHz
f=5.7 GHz
f=9.7 GHz
Elevation pattern (E-plane)
(b)
Fig. 11. Radiation Pattern of the CPW-fed PMEM Antenna. (a) Azimuthal Pattern (H-plane), (b)
Elevation Pattern (E-plane)
Ultra Wideband 356
3. Microstrip Slot UWB Antennas
Various printed slot antenna conﬁgurations such as rectangle (Jang, 2000), (Chiou, 2003),
(Chen, 2003) and (Liu, 2004), triangle (Chen, 2004) and (Chen, 2003), circle (Soliman, 1999) and

(Sze, 2006), arc
−shape (Chen, 2005), annular−ring (Chen, 2000) and others are proposed for
narrowband and wideband application. In (Lee, 2002), a round corner rectangular wide slot
antenna which is etched on a substrate with dimension of
(68 ×50)mm, the measure −10dB
bandwidth can achieve 6.17GHz (2.08GHz to 8.25GHz). In (Chen, 2003), a CPW square slot
antenna feed with a widened tuning stub can yield a wide impedance bandwidth of 60%. The
antenna has a dimension of
(72 ×72)mm and its gain ranges from 3.75dBi to 4.88dBi within
the operational band. It is shown that the achieved bandwidths of these antennas cannot cover
the whole FCC deﬁned UWB frequency band from 3.1 GHz to 10.6GHz. However, only a few
microstrip / CPW
−fed slot antennas with features suitable for UWB applications have been
demonstrated in the literature. In (Chair, 2004), a CPW
−fed rectangular slot antenna with a
U
−shaped tuning stub can provide a bandwidth of 110% with gain varying from 1.9dBi to
5.1dBi. Nevertheless, the antenna size is big
(100 × 100)mm. The same for (Angelopoulos,
2006), where a microstrip
−fed circular slot can operate over the entire UWB band, but with
a slot diameter of 65.2 mm. In (Denidni, 2006) and (Sorbello, 2005) UWB circular /elliptical
CPW
−fed slot and microstrip−fed antennas designs targeting the 3.1 − 10.6GHz band. The
antennas are comprised of elliptical or circular stubs that excite similar
−shaped slot aper-
tures. The same slots shapes were excited by a U
−shaped tuning stub in (Liang, 2006), where
an empirical formula is introduced to approximately determine the lower edge of the
−10dB

operating bandwidth. Others UWB slots antenna are proposed in (Sadat, 2007) and (Cheng,
2007). In this section, the microstrip
−fed PSICS antenna conﬁguration is investigated for
UWB communications.
Stepped Inverted Cone Slot Antennas
The conﬁguration of the proposed printed stepped inverted cone slot (PSICS) antenna is
shown in ﬁgure 12. The proposed antenna with different feeding stubs is designed to cover
the entire UWB band. The PSICS antenna consists of stepped inverted
−cone shaped stub on
the top side of
(50 ×52)mm(FR4, ε
r
= 4.32, loss tang of 0.017 and H = 1.59 mm in thickness)
fed by 50
−Ohms microstrip−line of width W
f
= 3mm. The ground plane with the inverted
stepped cone slot is printed on the bottom side.
A parametric study of the proposed PSICS UWB antenna on the main parameters of the
stepped inverted
−cone slot in the ground plane and the feeding stub structure are optimized
by using an electromagnetic simulator based on the Method of Moment (MoM).
The effect of the parameters R
s
, L
s1
, L
s2
, W
s1

, W
s2
and W
s3
which deﬁne the inverted−cone
shaped slot was carried out. The good frequency bandwidth (2.21GHz
− 11.5GHz) was found
for a radius R
s
= 20mm and the optimal values of the parameters L
s1
, L
s2
, W
s1
, W
s2
and W
s3
.
These values are presented in the table below.
Parameter L
s1
L
s2
W
s1
W
s2
W

s3
Optimal value (mm) 2 6 4.5 3.5 21.5
Table 1. Optimal Values of the Stepped Inverted-Cone Slot Parameters
Fig. 12. Geometry of the Microstrip-fed PSICS UWB Antenna
The tuning stub of the PSICS antenna has the same shape as the slot. It is also, deﬁned by the
radius R
t
and the parameters L
t1
, L
t1
, W
t1
, W
t2
and W
t3
, as shown in ﬁgure13.
Fig. 13. The Parameters of the Stepped Inverted-Cone Stub
The optimal feed tuning stub radius is found to be at R
t
= 10mm, with an extremely band-
width range from 2.21GHz to 11.5 GHz. Also, it seems that when the value of the parame-
ters L
t1
, L
t2
and L
t3
decrease, the ﬁrst resonance shift to the low frequency but the antenna

bandwidth decrease. The optimal values of the stepped
−inverted cone stub parameters are
presented in the table 2.
Design and characterization of microstrip UWB antennas 357
3. Microstrip Slot UWB Antennas
Various printed slot antenna conﬁgurations such as rectangle (Jang, 2000), (Chiou, 2003),
(Chen, 2003) and (Liu, 2004), triangle (Chen, 2004) and (Chen, 2003), circle (Soliman, 1999) and
(Sze, 2006), arc
−shape (Chen, 2005), annular−ring (Chen, 2000) and others are proposed for
narrowband and wideband application. In (Lee, 2002), a round corner rectangular wide slot
antenna which is etched on a substrate with dimension of
(68 ×50)mm, the measure −10dB
bandwidth can achieve 6.17GHz (2.08GHz to 8.25GHz). In (Chen, 2003), a CPW square slot
antenna feed with a widened tuning stub can yield a wide impedance bandwidth of 60%. The
antenna has a dimension of
(72 ×72)mm and its gain ranges from 3.75dBi to 4.88dBi within
the operational band. It is shown that the achieved bandwidths of these antennas cannot cover
the whole FCC deﬁned UWB frequency band from 3.1 GHz to 10.6GHz. However, only a few
microstrip / CPW
−fed slot antennas with features suitable for UWB applications have been
demonstrated in the literature. In (Chair, 2004), a CPW
−fed rectangular slot antenna with a
U
−shaped tuning stub can provide a bandwidth of 110% with gain varying from 1.9dBi to
5.1dBi. Nevertheless, the antenna size is big
(100 × 100)mm. The same for (Angelopoulos,
2006), where a microstrip
−fed circular slot can operate over the entire UWB band, but with
a slot diameter of 65.2 mm. In (Denidni, 2006) and (Sorbello, 2005) UWB circular /elliptical
CPW

−fed slot and microstrip−fed antennas designs targeting the 3.1 − 10.6GHz band. The
antennas are comprised of elliptical or circular stubs that excite similar
−shaped slot aper-
tures. The same slots shapes were excited by a U
−shaped tuning stub in (Liang, 2006), where
an empirical formula is introduced to approximately determine the lower edge of the
−10dB
operating bandwidth. Others UWB slots antenna are proposed in (Sadat, 2007) and (Cheng,
2007). In this section, the microstrip
−fed PSICS antenna conﬁguration is investigated for
UWB communications.
Stepped Inverted Cone Slot Antennas
The conﬁguration of the proposed printed stepped inverted cone slot (PSICS) antenna is
shown in ﬁgure 12. The proposed antenna with different feeding stubs is designed to cover
the entire UWB band. The PSICS antenna consists of stepped inverted
−cone shaped stub on
the top side of
(50 ×52)mm(FR4, ε
r
= 4.32, loss tang of 0.017 and H = 1.59 mm in thickness)
fed by 50
−Ohms microstrip−line of width W
f
= 3mm. The ground plane with the inverted
stepped cone slot is printed on the bottom side.
A parametric study of the proposed PSICS UWB antenna on the main parameters of the
stepped inverted
−cone slot in the ground plane and the feeding stub structure are optimized
by using an electromagnetic simulator based on the Method of Moment (MoM).
The effect of the parameters R

s
, L
s1
, L
s2
, W
s1
, W
s2
and W
s3
which deﬁne the inverted−cone
shaped slot was carried out. The good frequency bandwidth (2.21GHz
− 11.5GHz) was found
for a radius R
s
= 20mm and the optimal values of the parameters L
s1
, L
s2
, W
s1
, W
s2
and W
s3
.
These values are presented in the table below.
Parameter L
s1

L
s2
W
s1
W
s2
W
s3
Optimal value (mm) 2 6 4.5 3.5 21.5
Table 1. Optimal Values of the Stepped Inverted-Cone Slot Parameters
Fig. 12. Geometry of the Microstrip-fed PSICS UWB Antenna
The tuning stub of the PSICS antenna has the same shape as the slot. It is also, deﬁned by the
radius R
t
and the parameters L
t1
, L
t1
, W
t1
, W
t2
and W
t3
, as shown in ﬁgure13.
Fig. 13. The Parameters of the Stepped Inverted-Cone Stub
The optimal feed tuning stub radius is found to be at R
t
= 10mm, with an extremely band-
width range from 2.21GHz to 11.5 GHz. Also, it seems that when the value of the parame-

ters L
t1
, L
t2
and L
t3
decrease, the ﬁrst resonance shift to the low frequency but the antenna
bandwidth decrease. The optimal values of the stepped
−inverted cone stub parameters are
presented in the table 2.
Ultra Wideband 358
Parameter L
t1
L
t2
W
t1
W
t2
W
t3
Optimal value (mm) 2 4.5 6 3 4
Table 2. Optimal Values of the Stepped Inverted-Cone Stub Parameters
In order to optimize the coupling between the microstrip
−line and the stepped inverted−cone
slot. The stepped inverted
−cone stub was compared with two different stubs as shown in ﬁg-
ure 14. The ﬁrst one is an inverted-cone and the second stub has a circular shape.
Fig. 14. Different Stub Shapes Studied for the Microstrip-fed PSICS UWB Antenna
The return loss of the microstrip

−fed PSICS antenna was simulated for the three proposed
stubs. Figure 15 illustrates a comparison between simulated return loss curves.
It shown that all the proposed antenna stubs have similar return loss curves, with an ex-
Fig. 15. Return Loss Curves of the Microstrip-fed PSICS Antenna for Different Stubs
tremely
−10dB bandwidth which can covers the FCC UWB band. It is notice that the stepped
inverted-cone slot increase signiﬁcantly the possibility of the antenna feeding.
(a)
(
b)
(
c)
Fig. 16. Photographs of Realized Microstrip-fed PSICS Antennas. (a) with Stepped Inverted-Cone
Stub, (b) with Inverted-Cone Stub, (c) with Circular Stub
Three prototypes of the microstrip
−fed PSICS antenna with three different stubs in optimal
design, was fabricated and tested. Figures
(16.a), (16.b) and (16.c) present photos of PSICS
antenna with stepped inverted
−cone stub, inverted−cone stub and circular stub, respectively.
The return losses were measured by using vectorial network analyzer. Figures
(17.a), (17.b)
and (17.c) illustrate a comparison between simulated and measured return loss curves of
the PSICS antenna with stepped inverted-cone stub, inverted-cone stub and circular stub,
respectively. Generally speaking, as illustrated in ﬁgure
(17.a), the measured return loss curve
agrees with the simulated one in most range of the low frequencies band.
Design and characterization of microstrip UWB antennas 359
Parameter L
t1

L
t2
W
t1
W
t2
W
t3
Optimal value (mm) 2 4.5 6 3 4
Table 2. Optimal Values of the Stepped Inverted-Cone Stub Parameters
In order to optimize the coupling between the microstrip
−line and the stepped inverted−cone
slot. The stepped inverted
−cone stub was compared with two different stubs as shown in ﬁg-
ure 14. The ﬁrst one is an inverted-cone and the second stub has a circular shape.
Fig. 14. Different Stub Shapes Studied for the Microstrip-fed PSICS UWB Antenna
The return loss of the microstrip
−fed PSICS antenna was simulated for the three proposed
stubs. Figure 15 illustrates a comparison between simulated return loss curves.
It shown that all the proposed antenna stubs have similar return loss curves, with an ex-
Fig. 15. Return Loss Curves of the Microstrip-fed PSICS Antenna for Different Stubs
tremely
−10dB bandwidth which can covers the FCC UWB band. It is notice that the stepped
inverted-cone slot increase signiﬁcantly the possibility of the antenna feeding.
(a)
(b)
(c)
Fig. 16. Photographs of Realized Microstrip-fed PSICS Antennas. (a) with Stepped Inverted-Cone
Stub, (b) with Inverted-Cone Stub, (c) with Circular Stub
Three prototypes of the microstrip

−fed PSICS antenna with three different stubs in optimal
design, was fabricated and tested. Figures
(16.a), (16.b) and (16.c) present photos of PSICS
antenna with stepped inverted
−cone stub, inverted−cone stub and circular stub, respectively.
The return losses were measured by using vectorial network analyzer. Figures
(17.a), (17.b)
and (17.c) illustrate a comparison between simulated and measured return loss curves of
the PSICS antenna with stepped inverted-cone stub, inverted-cone stub and circular stub,
respectively. Generally speaking, as illustrated in ﬁgure
(17.a), the measured return loss curve
agrees with the simulated one in most range of the low frequencies band.
Ultra Wideband 360
(a)
(b)
(c)
Fig. 17. Comparison between Simulated and Measured Return loss Curves of the Microstrip-
fed PSICS UWB Antennas. (a) with Stepped Inverted-Cone Stub, (b) with Inverted-Cone Stub, (c)
with Circular Stub
The
−10dB bandwidth covers an extremely wide frequency range in both simulation and
measurement. In ﬁgure
(17.b), the UWB characteristic of the microstrip−fed PSICS antenna
with a circular stub is conﬁrmed in the measurement. It is shown that there is a good agree-
ment between simulated and measured lower edge frequencies. However, there is signiﬁcant
difference between simulated and measured high edge frequencies.
The far
−ﬁeld radiation patterns of the PSICS antennas were also simulated at three frequen-
cies. Figure 18 shows the radiation pattern of PSICS antenna with the inverted
−cone stub at

azimuthal and elevation planes. It is very important to note that the PSICS antenna with the
different feeding structures can provide similar radiation patterns. As can be seen from the
ﬁgure, omnidirectional patterns can be observed for the H
−plane.
Design and characterization of microstrip UWB antennas 361
(a)
(
b)
(c)
Fig. 17. Comparison between Simulated and Measured Return loss Curves of the Microstrip-
fed PSICS UWB Antennas. (a) with Stepped Inverted-Cone Stub, (b) with Inverted-Cone Stub, (c)
with Circular Stub
The
−10dB bandwidth covers an extremely wide frequency range in both simulation and
measurement. In ﬁgure
(17.b), the UWB characteristic of the microstrip−fed PSICS antenna
with a circular stub is conﬁrmed in the measurement. It is shown that there is a good agree-
ment between simulated and measured lower edge frequencies. However, there is signiﬁcant
difference between simulated and measured high edge frequencies.
The far
−ﬁeld radiation patterns of the PSICS antennas were also simulated at three frequen-
cies. Figure 18 shows the radiation pattern of PSICS antenna with the inverted
−cone stub at
azimuthal and elevation planes. It is very important to note that the PSICS antenna with the
different feeding structures can provide similar radiation patterns. As can be seen from the
ﬁgure, omnidirectional patterns can be observed for the H
−plane.
Ultra Wideband 362
(a)
(b)

Fig. 18. Radiation Pattern of the Microstrip-fed PSICS Antenna with Steped-Inverted Cone
Stub. (a) Azimuthal Pattern (H-plane), (b) Elevation Pattern (E-plane)
4. Microstrip Frequency Notched UWB Antennas
UWB technology is becoming an attractive solution for wireless communications, particu-
larly for short and medium-range applications. UWB systems operate over extremely wide
frequency bands (wider than 500MHz), according to the FCC regulations, the unlicensed us-
age of UWB systems for the indoor communications has been allocated to the spectrum from
3.1 to 10.6GHz. Within this UWB band, various narrowband technologies also operate with
much higher power levels, as illustrated in ﬁgure 19. It is clear, that there is frequency-band
sharing between the FCC’s UWB band and the IEEE 802.11a.
(5.15 − 5.825GHz) frequency
band and the wireless local area networks bands: HiperLAN (5.150 −5.350GHz) and WLAN
(5.725 −5.825GHz). Therefore, it may be necessary to have a notch for this band in order to
avoid interferences. Recently, various suppression techniques have been developed for UWB
communications to improve the performance, the capacity and the range. Some techniques
are used at the receiver stage, including notch ﬁltering (Choi et al, 1997), linear and nonlin-
ear predictive techniques (Rusch, 1994), (Rusch, 1995), (Proakis, 1995), (Carlemalm, 2002) and
(Azmi, 2002), adaptive methods (Lim et al., 1996) and (Fathallah et al., 1996), MMSE detectors
(Poor, 1997) and (Buzzi, 1996), and transform domain techniques (Buzzi et al., 1996), (Medley,
1997), (Weaver, 2003) and (Kasparis, 1991). Another approach for interference suppression is
used at the antenna. Based on this approach various frequency-notched UWB antennas have
been developed by inserting difﬁdent slot shapes (Chen, 2006), (Hong, 2007), (Yan, 2007),
(Yuan, 2008) and (Wang, 2008).
Fig. 19. The Coexistence of the UWB System and the Others Narrowband Systems
The advantage of this approach is that the stop-band ﬁlter (slot) is integrated directly in the an-
tenna structure, and this is very important for communication devices which become smaller
and more compact. In this section, we present the ability to achieve frequency notching char-
acteristics in the previous proposed PMEM antenna by using the U
−slot technique. The ge-
ometry of the notched-band PMEM antenna is shown in ﬁgure 20. The U

−shaped slot intro-
duced in the patch radiator is designed to notch the WLAN band.
Design and characterization of microstrip UWB antennas 363
(a)
(
b)
Fig. 18. Radiation Pattern of the Microstrip-fed PSICS Antenna with Steped-Inverted Cone
Stub. (a) Azimuthal Pattern (H-plane), (b) Elevation Pattern (E-plane)
4. Microstrip Frequency Notched UWB Antennas
UWB technology is becoming an attractive solution for wireless communications, particu-
larly for short and medium-range applications. UWB systems operate over extremely wide
frequency bands (wider than 500MHz), according to the FCC regulations, the unlicensed us-
age of UWB systems for the indoor communications has been allocated to the spectrum from
3.1 to 10.6GHz. Within this UWB band, various narrowband technologies also operate with
much higher power levels, as illustrated in ﬁgure 19. It is clear, that there is frequency-band
sharing between the FCC’s UWB band and the IEEE 802.11a.
(5.15 − 5.825GHz) frequency
band and the wireless local area networks bands: HiperLAN (5.150 −5.350GHz) and WLAN
(5.725 −5.825GHz). Therefore, it may be necessary to have a notch for this band in order to
avoid interferences. Recently, various suppression techniques have been developed for UWB
communications to improve the performance, the capacity and the range. Some techniques
are used at the receiver stage, including notch ﬁltering (Choi et al, 1997), linear and nonlin-
ear predictive techniques (Rusch, 1994), (Rusch, 1995), (Proakis, 1995), (Carlemalm, 2002) and
(Azmi, 2002), adaptive methods (Lim et al., 1996) and (Fathallah et al., 1996), MMSE detectors
(Poor, 1997) and (Buzzi, 1996), and transform domain techniques (Buzzi et al., 1996), (Medley,
1997), (Weaver, 2003) and (Kasparis, 1991). Another approach for interference suppression is
used at the antenna. Based on this approach various frequency-notched UWB antennas have
been developed by inserting difﬁdent slot shapes (Chen, 2006), (Hong, 2007), (Yan, 2007),
(Yuan, 2008) and (Wang, 2008).
Fig. 19. The Coexistence of the UWB System and the Others Narrowband Systems

The advantage of this approach is that the stop-band ﬁlter (slot) is integrated directly in the an-
tenna structure, and this is very important for communication devices which become smaller
and more compact. In this section, we present the ability to achieve frequency notching char-
acteristics in the previous proposed PMEM antenna by using the U
−slot technique. The ge-
ometry of the notched-band PMEM antenna is shown in ﬁgure 20. The U
−shaped slot intro-
duced in the patch radiator is designed to notch the WLAN band.
Ultra Wideband 364
Fig. 20. Geometry of the Notched-Band Microstrip-fed PMEM UWB Antenna
The optimal values (in mm) of the patch radiator and the ground plane are presented in the
table 3.
Parameter L
t1
L
t2
W
t1
W
t2
W
t3
Optimal value (mm) 2 4.5 6 3 4
Table 3. Optimal Values of the U-Shape Slot
Band-notch function study
The inﬂuence of the parameters L
1
, L
2
, W

1
, and W
2
of the U-shaped slot introduced in the
patch radiator are studied. To see the inﬂuences on the performance of the antenna an EM
simulator is used. It is seen that by embedding the U
−slot on the radiation patch, band-
notched characteristic is obtained.
Figure
(21.a), shows the VSWR of the antenna with different L
1
of the slot location as the
length L
2
are ﬁxed at 0.75mm. It is seen that when L
1
is between 4.1mm and 4.3mm , the
antenna has a band-notch function at the WLAN band.
Figure
(21.b) shows the VSWR of the antenna for different values of L
2
. It is seen that the
length of the slot determines the frequency range of the notched band. As L
2
increases, the
notched band shifts toward the higher frequency. It is found that by adjusting the length of
slot to be about 0.75mm a notched frequency band of about 5.6
−5.95GHz is obtained.
Figures
(22.a) and (22.b) show the VSWR of the antenna with different slot widths W

1
and
W
2
, respectively. It is seen that when W
1
is smaller than 2mm, the antenna has a band-notch
function at the WLAN band.
(a)
(
b)
Fig. 21. VSWR versus U-Shape Slot Parameters. (a) The Effect of L1, (b) The Effect of L2
Design and characterization of microstrip UWB antennas 365
Fig. 20. Geometry of the Notched-Band Microstrip-fed PMEM UWB Antenna
The optimal values (in mm) of the patch radiator and the ground plane are presented in the
table 3.
Parameter L
t1
L
t2
W
t1
W
t2
W
t3
Optimal value (mm) 2 4.5 6 3 4
Table 3. Optimal Values of the U-Shape Slot
Band-notch function study
The inﬂuence of the parameters L

1
, L
2
, W
1
, and W
2
of the U-shaped slot introduced in the
patch radiator are studied. To see the inﬂuences on the performance of the antenna an EM
simulator is used. It is seen that by embedding the U
−slot on the radiation patch, band-
notched characteristic is obtained.
Figure
(21.a), shows the VSWR of the antenna with different L
1
of the slot location as the
length L
2
are ﬁxed at 0.75mm. It is seen that when L
1
is between 4.1mm and 4.3mm , the
antenna has a band-notch function at the WLAN band.
Figure
(21.b) shows the VSWR of the antenna for different values of L
2
. It is seen that the
length of the slot determines the frequency range of the notched band. As L
2
increases, the
notched band shifts toward the higher frequency. It is found that by adjusting the length of

slot to be about 0.75mm a notched frequency band of about 5.6
−5.95GHz is obtained.
Figures
(22.a) and (22.b) show the VSWR of the antenna with different slot widths W
1
and
W
2
, respectively. It is seen that when W
1
is smaller than 2mm, the antenna has a band-notch
function at the WLAN band.
(a)
(b)
Fig. 21. VSWR versus U-Shape Slot Parameters. (a) The Effect of L1, (b) The Effect of L2
Ultra Wideband 366
(a)
2 3 4 5 6 7 8 9 10 11 12
1
2
3
4
5
6
7
8
9
10
11
12

VSWR
Frequency [GHz]
W2=6mm
W2=5.5mm
W2=5mm
W2=4.5mm
W2=4mm
(b)
Fig. 22. VSWR versus U-Shape Slot Parameters. (a) The Effect of W1, (b) The Effect of W2
A prototype of the microstrip-fed notched-band PMEM antenna with optimal design, was
fabricated as shown in ﬁgure 10. A comparison between simulated return loss and measured
return loss obtained by using a VNA is shown in ﬁgure 24.
(a) (b)
Fig. 23. Photographs of Realized Notched-Band PMEM UWB Antenna. (a) Top Side, (b) Back
Side
Fig. 24. Comparison between Simulated and Measured VSWR Curves of the Notched-Band
Microstrip-fed PMEM UWB Antenna
Design and characterization of microstrip UWB antennas 367
(a)
2 3 4 5 6 7 8 9 10 11 12
1
2
3
4
5
6
7
8
9
10

11
12
VSWR
Frequency [GHz]
W2=6mm
W2=5.5mm
W2=5mm
W2=4.5mm
W2=4mm
(b)
Fig. 22. VSWR versus U-Shape Slot Parameters. (a) The Effect of W1, (b) The Effect of W2
A prototype of the microstrip-fed notched-band PMEM antenna with optimal design, was
fabricated as shown in ﬁgure 10. A comparison between simulated return loss and measured
return loss obtained by using a VNA is shown in ﬁgure 24.
(a) (b)
Fig. 23. Photographs of Realized Notched-Band PMEM UWB Antenna. (a) Top Side, (b) Back
Side
Fig. 24. Comparison between Simulated and Measured VSWR Curves of the Notched-Band
Microstrip-fed PMEM UWB Antenna
Ultra Wideband 368
It is shown that there is a good agreement between simulated and measured VSWR curves
at the most range. However, after the frequency 10.4GHz the measured VSWR will be
greater than 2, where the simulated one remains less than 2. In other words a frequency-
notch function at WLAN band is investigated. This characteristic is very attractive for UWB
applications.
5. Acknowledgement
The authors acknowledge Dr. Attrouz, B. chief of Microwave and radar laboratory at Military
Polytechnic School (EMP) in Algeria for his help in antenna prototypes realization/measurement
and his very useful discussions and motivation.
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Design and characterization of microstrip UWB antennas 369
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at the most range. However, after the frequency 10.4GHz the measured VSWR will be
greater than 2, where the simulated one remains less than 2. In other words a frequency-
notch function at WLAN band is investigated. This characteristic is very attractive for UWB
applications.
5. Acknowledgement
The authors acknowledge Dr. Attrouz, B. chief of Microwave and radar laboratory at Military
Polytechnic School (EMP) in Algeria for his help in antenna prototypes realization/measurement
and his very useful discussions and motivation.
6. References

Kasparis, T. (1991). Frequency independent sinusoidal suppression using median ﬁlters. IEEE
Int. Conf. Acoustics, Speech, Signal Processing (ICASSP), pp. 612-615,Toronto, April,
1991
Kimouche, H.; Abed, D. & Atrouz, B. (2009). Investigation on Microstrip-fed Modiﬁed Ellipti-
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ence on Antennas and Propagation (EuCAP), pp. 1450 - 1454, Berlin, Germany, March
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Kobayashi, H. sasamori, T. Tobana, T. and Abe, K. (2007). A Study on Miniaturization of
Printed Disc Monopole Antenna for UWB Applications Using Notched Ground
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Lee, H L., Lee, H J., Yook, J. -G. and Park, H. K. (2002). Broadband Planar Antenna having
Round Corner Rectangular Wide Slot. Antennas and Propagation Society Interna-
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Liang, P.Li. and Chen,X. (2006). Study of Printed Elliptical/Circular Slot Antennas for Ultraw-
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UWB antennas: design and modeling 371
UWB antennas: design and modeling

Yvan Duroc and Ali-Imran Najam
X

UWB antennas: design and modeling

Yvan Duroc and Ali-Imran Najam
Grenoble Institute of Technology
France

1. Introduction
1.1 Brief history of antennas and their evolution
The antenna is an essential part of any wireless system as it is the component providing
transition between a guided wave and a free-space wave. According to the IEEE standard
definitions of terms for antennas (IEEE, 1993), an antenna is defined as a means for radiating
or receiving radio waves. During the period 1885-1900, some pioneers invented the antennas
and the wireless systems. The wire antennas were inaugurated in 1842 by the inventor of
telegraphy, Joseph Henry who had also discovered electromagnetic waves and had even
formulated the idea that light waves were of this type. About forty years later, the antennas
and the first wireless systems emerged. In 1885, Edison patented a communication system
using vertical, top-loaded and grounded antennas. In 1887, Hertz launched, processed and
received radio using a balanced or dipole antenna as a transmitter and a one-turn loop
containing a spark gap as a receiver. The invention of antenna is credited to Popov who
proposed a device capable of detecting electromagnetic waves in the atmosphere and
introduced the concept of antenna in 1895. The initial concepts of phase arrays were
proposed in 1889. Several advances in antennas were patented in 1897 by Lodge and these
contributions yielded matching, tuning, and addition of the word “impedance” to the
language. Finally, the first most significant application was the telegraph of Marconi
patented in 1900.
Many decades after these early investigations, the antenna has drawn a lot of attention over
the years and has remained a subject of numerous challenges. Although dipole and loop

antennas are still widely used for various radio systems, yet the antennas have been evolved
remarkably with respect to both their topologies and usages. Research conducted on
antennas is driven by several factors. The first factor deals with the increase of the
bandwidth and shift of operational frequency to the higher bands. With the ever-increasing
need for mobile communication and the emergence of many systems, it has become
important to design broadband antennas to cover a wide frequency range. Modern wireless
applications require the processing of more and more data in different forms, higher data
rates, higher capacity and multi-standard abilities. There are numerous well-known
methods to increase the bandwidth of antennas including designs with log-periodic profile,
travelling-wave topologies, increase of the substrate thickness and the use of a low dielectric
substrate, various impedance matching and feeding techniques, multiple resonators and slot
antenna geometry (Walter, 1990; Agrawal et al., 1997; Amman & Chen, 2003a; Islam, 2009).
16
Ultra Wideband 372

The second factor deals with field pattern and the ways to control it. One method is to use a
multitude of identical radiating elements to form an array. The elementary antennas are fed
from a single source through a network of transmission line and/or waveguides. In such
systems, the shape of the radiation pattern is governed by the field pattern of the elementary
antenna (which is chosen to be as simple as possible), the power distribution among the
elements and geometric details of their arrangement. Many examples are available in the
literature (Chang, 1997). Even if the arrays were initially designed for high power purposes
using bulk antennas, but their developments in planar and integrated forms using
microstrip patches are more attractive (Munson, 1974). The third factor deals with isotropic
behavior, i.e., the ability of antennas to radiate equally in all directions. Indeed in the context
of wireless sensor networks, radio frequency identification or millimetre-length
communications, the random and time-varying orientations of the devices with respect to
each other cause strong variations of the transmitted signal due to the radiation anisotropy
and polarization mismatches of antennas. Ad-hoc sensor networks for human motion
capture systems based on wearable sensors as well as the localization of mobile objects are

typical upcoming applications requiring quite constant received power whatever be the
orientations of devices relative to each other (Puccinelli & Haenggi, 2005). Directions of
departure and arrival of a beam can totally change while in use and fall into antenna
radiating null. Polarization mismatches can also cause fading of the transmitted power. It is
therefore difficult to maintain the quality of service. Isotropic antenna is a hypothetical
idealized device that does not exist in reality (Mathis, 1951). A close approximation can be a
stack of two pairs of crossed dipole antennas driven in quadrature. When space has to be
covered in all directions, smart antennas with pattern and polarization agility are required.
However, for many applications, generalizations of adaptive smart antenna are still far
away due to their high cost or power consumption or because of size and integration issues.
Consequently, there is a need for small antennas with optimized radiation pattern and
polarization to provide wide coverage. One method to obtain quasi-isotropy behavior is to
associate several elementary antennas in complementary way in terms of fields and
polarization. The concept of spatial coverage factor as well as its application to a quasi-
isotropic antenna has been introduced (Huchard et al., 2005). According to wireless
applications and the associated devices, the type of antennas can be very different. For
example, the main requirements for an antenna of a cellular mobile radio phone will be
small type, low profile and broad/multi bandwidth.
Last but not least, in modern wireless communication systems, complex signal processing
techniques and digital routines are considered in order to build a device which is flexible
enough to run every possible waveform without any restrictions on carrier frequency,
bandwidth, modulation format, date rate, etc. This is the philosophy of future radio systems
such as Software Defined Radio (SDR) and cognitive radio firstly introduced by Mitola
(Mitola, 1995; Mitola and Maguire, 1999). In this context, the antenna becomes not only one
of the most important parts in a wireless system but it is also flexible and “intelligent”
enough to perform processing function that can be realized by any other device. The
antennas are becoming increasingly linked to other components (e.g., system-on-chip) and
to other subject areas (such as digital signal processing or propagation channels). To
accurately integrate the antenna performance into the design of the overall wireless system,
specific models compatible with standard languages are highly desired. Such modeling

allows the right design and optimization of wireless RF front-ends including antennas.

1.2 Ultra Wideband technology
Ultra Wideband (UWB) is an emerging technology for future short-range wireless
communications with high data rates as well as radar and geolocation (Yang & Giannakis,
2004). Indeed, the use of large bandwidths offers multiple benefits including high date rates,
robustness to propagation fading, accurate ranging and geolocation, superior obstacle
penetration, resistance to jamming, interference rejection, and coexistence with narrow
bandwidth systems. It should be noted that the first UWB signals were generated in
experiments by Hertz who radiated sparks via wideband loaded dipoles. However, this
type of communication was abandoned at that time due to non-availability of resources to
recover the wideband energy effectively. Later during the 1960s and 1970s, impulse radio
technologies were being used to develop radar, sensing, military communications and niche
applications. A landmark patent in UWB communications was submitted by Ross in 1973.
However, it was in 1989 that the term “Ultra Wideband” appeared in a publication of
department of defense in the United States (U.S.) and the first patent with the exact phrase
“UWB antenna” was filed on behalf of Hughes in 1993. Thus, interest in UWB was revived
in the 1990s thanks to the improvements in digital signal processing and notably the
investigation on Impulse Radio (IR) by Win and Scholtz (Win & Scholtz, 1998). Finally, it
was in 2002 when the interest for UWB systems was greatly magnified by the decision of the
United States frequency regulating body, the Federal Communications Commission (FCC),
who released a report approving the use of UWB devices operating in several unlicensed
frequency bands [0-960 MHz], [3.1-10.6 GHz], and [22-29 GHz]. Since then, regulations were
defined through notably emission spectral masks around the world,. In Europe, the
Electronic Communications Committee (ECC) has proposed its most recent proposal in
April 2009. In contrast to the FCC’s single emission mask level over the entire UWB band,
this report proposed two sub-bands with the low band ranging from 3.1 GHz to 4.8 GHz
(authorized until 2011 with mitigation techniques included to ensure coexistence) and the
high band from 6 GHz to 8.5 GHz. The upper bound for Effective Isotropic Radiation Power
(EIRP) is common and has been set out to be - 41.3 dBm/MHz. Even if the authorized

frequency bands are different according to the world regions, the definition of UWB is
universal. UWB describes wireless physical layer technology which uses a bandwidth of at
least 500 MHz or a bandwidth which is at least 20% of the central frequency in use. Two
approaches have been developed for UWB systems: pulsed operation and multiple narrow
bands. Among these techniques, the original approach is based on IR concept. Impulse
Radio refers to the use of a series of very short duration pulses, which are modulated in
position or/and amplitude. As signals are carrier-less, i.e., only baseband signals exist;
therefore no intermediate frequency processing is needed. Alternative schemes are Multi-
Band Orthogonal Frequency Division Multiplexing (MB-OFDM) and Multi-Carrier Code
Division Multiple Access (MC-CDMA).
To guarantee the coexistence of UWB with other communication standards, the authorized
transmitted power is always very low which limits the development of UWB
communication systems with very high data rates and/or the coverage of larger distances.
The association of Multiple Input Multiple Output (MIMO) systems (which exploit rich
scattering environments by the use of multiple antennas) with UWB technology is more and
more studied. It seems to be a very potential approach for enhancing capacity, increasing
range, raising link reliability and improving interference cancellation (Siriwongpairat et al.,
2004; Yang & Giannakis, 2004; Kaiser et al., 2006). Recent works have also shown the
UWB antennas: design and modeling 373

The second factor deals with field pattern and the ways to control it. One method is to use a
multitude of identical radiating elements to form an array. The elementary antennas are fed
from a single source through a network of transmission line and/or waveguides. In such
systems, the shape of the radiation pattern is governed by the field pattern of the elementary
antenna (which is chosen to be as simple as possible), the power distribution among the
elements and geometric details of their arrangement. Many examples are available in the
literature (Chang, 1997). Even if the arrays were initially designed for high power purposes
using bulk antennas, but their developments in planar and integrated forms using
microstrip patches are more attractive (Munson, 1974). The third factor deals with isotropic
behavior, i.e., the ability of antennas to radiate equally in all directions. Indeed in the context

of wireless sensor networks, radio frequency identification or millimetre-length
communications, the random and time-varying orientations of the devices with respect to
each other cause strong variations of the transmitted signal due to the radiation anisotropy
and polarization mismatches of antennas. Ad-hoc sensor networks for human motion
capture systems based on wearable sensors as well as the localization of mobile objects are
typical upcoming applications requiring quite constant received power whatever be the
orientations of devices relative to each other (Puccinelli & Haenggi, 2005). Directions of
departure and arrival of a beam can totally change while in use and fall into antenna
radiating null. Polarization mismatches can also cause fading of the transmitted power. It is
therefore difficult to maintain the quality of service. Isotropic antenna is a hypothetical
idealized device that does not exist in reality (Mathis, 1951). A close approximation can be a
stack of two pairs of crossed dipole antennas driven in quadrature. When space has to be
covered in all directions, smart antennas with pattern and polarization agility are required.
However, for many applications, generalizations of adaptive smart antenna are still far
away due to their high cost or power consumption or because of size and integration issues.
Consequently, there is a need for small antennas with optimized radiation pattern and
polarization to provide wide coverage. One method to obtain quasi-isotropy behavior is to
associate several elementary antennas in complementary way in terms of fields and
polarization. The concept of spatial coverage factor as well as its application to a quasi-
isotropic antenna has been introduced (Huchard et al., 2005). According to wireless
applications and the associated devices, the type of antennas can be very different. For
example, the main requirements for an antenna of a cellular mobile radio phone will be
small type, low profile and broad/multi bandwidth.
Last but not least, in modern wireless communication systems, complex signal processing
techniques and digital routines are considered in order to build a device which is flexible
enough to run every possible waveform without any restrictions on carrier frequency,
bandwidth, modulation format, date rate, etc. This is the philosophy of future radio systems
such as Software Defined Radio (SDR) and cognitive radio firstly introduced by Mitola
(Mitola, 1995; Mitola and Maguire, 1999). In this context, the antenna becomes not only one
of the most important parts in a wireless system but it is also flexible and “intelligent”

enough to perform processing function that can be realized by any other device. The
antennas are becoming increasingly linked to other components (e.g., system-on-chip) and
to other subject areas (such as digital signal processing or propagation channels). To
accurately integrate the antenna performance into the design of the overall wireless system,
specific models compatible with standard languages are highly desired. Such modeling
allows the right design and optimization of wireless RF front-ends including antennas.

1.2 Ultra Wideband technology
Ultra Wideband (UWB) is an emerging technology for future short-range wireless
communications with high data rates as well as radar and geolocation (Yang & Giannakis,
2004). Indeed, the use of large bandwidths offers multiple benefits including high date rates,
robustness to propagation fading, accurate ranging and geolocation, superior obstacle
penetration, resistance to jamming, interference rejection, and coexistence with narrow
bandwidth systems. It should be noted that the first UWB signals were generated in
experiments by Hertz who radiated sparks via wideband loaded dipoles. However, this
type of communication was abandoned at that time due to non-availability of resources to
recover the wideband energy effectively. Later during the 1960s and 1970s, impulse radio
technologies were being used to develop radar, sensing, military communications and niche
applications. A landmark patent in UWB communications was submitted by Ross in 1973.
However, it was in 1989 that the term “Ultra Wideband” appeared in a publication of
department of defense in the United States (U.S.) and the first patent with the exact phrase
“UWB antenna” was filed on behalf of Hughes in 1993. Thus, interest in UWB was revived
in the 1990s thanks to the improvements in digital signal processing and notably the
investigation on Impulse Radio (IR) by Win and Scholtz (Win & Scholtz, 1998). Finally, it
was in 2002 when the interest for UWB systems was greatly magnified by the decision of the
United States frequency regulating body, the Federal Communications Commission (FCC),
who released a report approving the use of UWB devices operating in several unlicensed
frequency bands [0-960 MHz], [3.1-10.6 GHz], and [22-29 GHz]. Since then, regulations were
defined through notably emission spectral masks around the world,. In Europe, the
Electronic Communications Committee (ECC) has proposed its most recent proposal in

April 2009. In contrast to the FCC’s single emission mask level over the entire UWB band,
this report proposed two sub-bands with the low band ranging from 3.1 GHz to 4.8 GHz
(authorized until 2011 with mitigation techniques included to ensure coexistence) and the
high band from 6 GHz to 8.5 GHz. The upper bound for Effective Isotropic Radiation Power
(EIRP) is common and has been set out to be - 41.3 dBm/MHz. Even if the authorized
frequency bands are different according to the world regions, the definition of UWB is
universal. UWB describes wireless physical layer technology which uses a bandwidth of at
least 500 MHz or a bandwidth which is at least 20% of the central frequency in use. Two
approaches have been developed for UWB systems: pulsed operation and multiple narrow
bands. Among these techniques, the original approach is based on IR concept. Impulse
Radio refers to the use of a series of very short duration pulses, which are modulated in
position or/and amplitude. As signals are carrier-less, i.e., only baseband signals exist;
therefore no intermediate frequency processing is needed. Alternative schemes are Multi-
Band Orthogonal Frequency Division Multiplexing (MB-OFDM) and Multi-Carrier Code
Division Multiple Access (MC-CDMA).
To guarantee the coexistence of UWB with other communication standards, the authorized
transmitted power is always very low which limits the development of UWB
communication systems with very high data rates and/or the coverage of larger distances.
The association of Multiple Input Multiple Output (MIMO) systems (which exploit rich
scattering environments by the use of multiple antennas) with UWB technology is more and
more studied. It seems to be a very potential approach for enhancing capacity, increasing
range, raising link reliability and improving interference cancellation (Siriwongpairat et al.,
2004; Yang & Giannakis, 2004; Kaiser et al., 2006). Recent works have also shown the
Ultra Wideband 374

prospects of using the UWB technology into the next generation RFID (Radio Frequency
Identification) systems. Indeed, promises have been highlighted in order to achieve larger
operating range, accurate localization, robustness to interference and more security in
multiple access systems (Zou et al., 2007; Hu et al., 2007; Dardari & D’Errico, 2008). Further,
when the wireless systems that are potential candidates for cognitive radio are considered,

UWB seems to be one of the tempting choices because it has an inherent potential to fulfill
some of the key requirements of cognitive radio (Manteuffel et al.; 2009). These
requirements include no spurious interference to licensed systems, adjustable pulse shape,
bandwidth and transmitted power, support of various throughputs, provision of adaptive
multiple access, and security of information. However, it is not claimed that a cognitive
wireless system using only the UWB technology can handle all the requirements of an ideal
cognitive radio. Advances in reconfigurability of RF front-ends, particularly reconfigurable
(multiple) antennas, afford a new “hardware” dimension for optimizing the performance of
wireless communication systems (Sayeed & Raghavan, 2007).
The prospects of UWB are always growing, however, the future wireless systems using
UWB technology involve many new challenges, especially, related to the design and
modeling of UWB antennas. Section 2 presents an overview of different categories of UWB
(single and multiple) antennas emphasizing their main properties. Section 3 focuses on the
approaches for the characterization and modeling of UWB antennas. Conclusions and
perspectives are presented in the last section.

2. Design of Ultra Wideband Antennas
2.1 UWB antenna properties
An antenna is a device that converts a signal transmitted from a source to a transmission
line into electromagnetic waves to be broadcasted into free space and vice versa. An antenna
is usually required to optimize or concentrate the radiation energy in some directions and to
suppress it in the others at certain frequencies. A good design of the antenna can relax
system requirements and improve overall system performance. In practice, to describe the
performance of an antenna, there are several commonly used antenna parameters, such as
impedance bandwidth, radiation pattern, directivity, gain, input impedance, and so on.
Particularly, a UWB antenna is defined as an antenna having a fractional bandwidth greater
than 0.2 and a minimum bandwidth of 500 MHz.

MHz500ffand2.0
ff

ff
2BW
LH
LH
LH




(1)

where f
L
and f
H
are the frequencies defining the antenna’s operational band. For example, an
IR-UWB system, which would comply with the emission mask and operate within the 3.1-
10.6 GHz frequency range allocated in U.S, needs an antenna achieving almost a decade of
impedance bandwidth spanning 7.5 GHz.
However, UWB antennas are firstly antennas! As a consequence, UWB antennas try to
achieve the same goals, and are subjected to the same physical constraints (e.g., low cost,
small size, integration capability, etc.) and the same electrical constraints (e.g., impedance
matching, radiation pattern, directivity, efficiency, polarization, etc.) as in the case of
narrowband antennas. Further, due to the large bandwidth, the electrical parameters

become frequency dependent complicating the design and analysis. In addition to the
conventional characterization parameters, some specific parameters must be examined in
order to take into account the distortion effects, notably, critical for IR applications. These
specific parameters include group delay, phase response and impulse response. The
radiation pattern is desired to be constant within the overall operating frequency in order to

guarantee the pulse properties to be same in any direction. The group delay is given by the
derivative of the unwrapped phase of an antenna. If the phase is linear throughout the
frequency range, the group delay will be constant for the frequency range. This is an
important characteristic because it helps to indicate how well a UWB pulse will be
transmitted and to what degree it may be distorted or dispersed.
The specifications of the antenna design will be a trade-off of these parameters taking into
account not only the expected application but also the technique of transmission (multiple
narrow bands or pulsed operation) to be used. Some parameters have to be declared more
important than others. Two types of requirements can be distinguished. The physical
constraints arise when one strives to develop antennas of small size, low profile and low
cost (materials, maintenance and fabrication), and with embeddable capability. The
electrical constraints arise while designing antennas with wideband impedance bandwidth
covering all sub-bands (for MB-OFDM) or the bandwidth where most of the energy of the
source pulse is concentrated (for IR), steady directional or omni-directional radiation
patterns, constant gain at directions of interest, constant desired polarization, high radiation
efficiency and linear phase response (for IR).

2.2 UWB antenna characteristics
In 2003, a history of UWB antennas is presented by H.G. Schantz who emphasizes the
relevant past works on UWB antennas and their important wide variety (Schantz, 2003):
“Ultra-Wideband has its roots in the original spark-gap transmitters that pioneered radio technology.
This history is well known and has been well documented in both professional histories and in
popular treatments. The development of UWB antennas has not been subjected to similar scrutiny.
As a consequence, designs have been forgotten and then re-discovered by later investigators”.
Thus, in the recent years, a lot of UWB antenna designs have been reported and presented in
the academic literature (Schantz, 2005; Wiesbeck & Adamiuk, 2007; Chang, 2008) and in
some patents (Akdagli et al., 2008). The main challenge to design a UWB antenna comes
from the coverage of large bandwidth because the matching and energy transmission
require to be verified for the entire bandwidth. However, the traditional trade-offs such as
size vs. efficiency and size vs. bandwidth (Chu-Harrington limit) still influence the

characteristics and performance of antennas.
UWB antennas may be categorized into different types according to their radiating
characteristics: frequency independent antennas, multi-resonant antennas, travelling wave
antennas and small element antennas.

2.2.1 Frequency independent antennas
Frequency independent antennas, such as biconical, spiral, conical spiral and log periodic
antennas are classic broadband and UWB antennas. They can offer real constant impedances
and consistent pattern properties over a frequency bandwidth greater than 10:1. There are
two principles for achieving frequency independent characteristics.
UWB antennas: design and modeling 375

prospects of using the UWB technology into the next generation RFID (Radio Frequency
Identification) systems. Indeed, promises have been highlighted in order to achieve larger
operating range, accurate localization, robustness to interference and more security in
multiple access systems (Zou et al., 2007; Hu et al., 2007; Dardari & D’Errico, 2008). Further,
when the wireless systems that are potential candidates for cognitive radio are considered,
UWB seems to be one of the tempting choices because it has an inherent potential to fulfill
some of the key requirements of cognitive radio (Manteuffel et al.; 2009). These
requirements include no spurious interference to licensed systems, adjustable pulse shape,
bandwidth and transmitted power, support of various throughputs, provision of adaptive
multiple access, and security of information. However, it is not claimed that a cognitive
wireless system using only the UWB technology can handle all the requirements of an ideal
cognitive radio. Advances in reconfigurability of RF front-ends, particularly reconfigurable
(multiple) antennas, afford a new “hardware” dimension for optimizing the performance of
wireless communication systems (Sayeed & Raghavan, 2007).
The prospects of UWB are always growing, however, the future wireless systems using
UWB technology involve many new challenges, especially, related to the design and
modeling of UWB antennas. Section 2 presents an overview of different categories of UWB
(single and multiple) antennas emphasizing their main properties. Section 3 focuses on the

approaches for the characterization and modeling of UWB antennas. Conclusions and
perspectives are presented in the last section.

2. Design of Ultra Wideband Antennas
2.1 UWB antenna properties
An antenna is a device that converts a signal transmitted from a source to a transmission
line into electromagnetic waves to be broadcasted into free space and vice versa. An antenna
is usually required to optimize or concentrate the radiation energy in some directions and to
suppress it in the others at certain frequencies. A good design of the antenna can relax
system requirements and improve overall system performance. In practice, to describe the
performance of an antenna, there are several commonly used antenna parameters, such as
impedance bandwidth, radiation pattern, directivity, gain, input impedance, and so on.
Particularly, a UWB antenna is defined as an antenna having a fractional bandwidth greater
than 0.2 and a minimum bandwidth of 500 MHz.

MHz500ffand2.0
ff
ff
2BW
LH
LH
LH




(1)

where f
L

and f
H
are the frequencies defining the antenna’s operational band. For example, an
IR-UWB system, which would comply with the emission mask and operate within the 3.1-
10.6 GHz frequency range allocated in U.S, needs an antenna achieving almost a decade of
impedance bandwidth spanning 7.5 GHz.
However, UWB antennas are firstly antennas! As a consequence, UWB antennas try to
achieve the same goals, and are subjected to the same physical constraints (e.g., low cost,
small size, integration capability, etc.) and the same electrical constraints (e.g., impedance
matching, radiation pattern, directivity, efficiency, polarization, etc.) as in the case of
narrowband antennas. Further, due to the large bandwidth, the electrical parameters

become frequency dependent complicating the design and analysis. In addition to the
conventional characterization parameters, some specific parameters must be examined in
order to take into account the distortion effects, notably, critical for IR applications. These
specific parameters include group delay, phase response and impulse response. The
radiation pattern is desired to be constant within the overall operating frequency in order to
guarantee the pulse properties to be same in any direction. The group delay is given by the
derivative of the unwrapped phase of an antenna. If the phase is linear throughout the
frequency range, the group delay will be constant for the frequency range. This is an
important characteristic because it helps to indicate how well a UWB pulse will be
transmitted and to what degree it may be distorted or dispersed.
The specifications of the antenna design will be a trade-off of these parameters taking into
account not only the expected application but also the technique of transmission (multiple
narrow bands or pulsed operation) to be used. Some parameters have to be declared more
important than others. Two types of requirements can be distinguished. The physical
constraints arise when one strives to develop antennas of small size, low profile and low
cost (materials, maintenance and fabrication), and with embeddable capability. The
electrical constraints arise while designing antennas with wideband impedance bandwidth
covering all sub-bands (for MB-OFDM) or the bandwidth where most of the energy of the

source pulse is concentrated (for IR), steady directional or omni-directional radiation
patterns, constant gain at directions of interest, constant desired polarization, high radiation
efficiency and linear phase response (for IR).

2.2 UWB antenna characteristics
In 2003, a history of UWB antennas is presented by H.G. Schantz who emphasizes the
relevant past works on UWB antennas and their important wide variety (Schantz, 2003):
“Ultra-Wideband has its roots in the original spark-gap transmitters that pioneered radio technology.
This history is well known and has been well documented in both professional histories and in
popular treatments. The development of UWB antennas has not been subjected to similar scrutiny.
As a consequence, designs have been forgotten and then re-discovered by later investigators”.
Thus, in the recent years, a lot of UWB antenna designs have been reported and presented in
the academic literature (Schantz, 2005; Wiesbeck & Adamiuk, 2007; Chang, 2008) and in
some patents (Akdagli et al., 2008). The main challenge to design a UWB antenna comes
from the coverage of large bandwidth because the matching and energy transmission
require to be verified for the entire bandwidth. However, the traditional trade-offs such as
size vs. efficiency and size vs. bandwidth (Chu-Harrington limit) still influence the
characteristics and performance of antennas.
UWB antennas may be categorized into different types according to their radiating
characteristics: frequency independent antennas, multi-resonant antennas, travelling wave
antennas and small element antennas.

2.2.1 Frequency independent antennas
Frequency independent antennas, such as biconical, spiral, conical spiral and log periodic
antennas are classic broadband and UWB antennas. They can offer real constant impedances
and consistent pattern properties over a frequency bandwidth greater than 10:1. There are
two principles for achieving frequency independent characteristics.
Ultra Wideband 376

The first one was introduced by Rumsey in the 1950s. Rumsey’s principle suggests that the

pattern properties of an antenna will be frequency independent if the antenna shape is
specified only in terms of angles. Infinite biconical and spiral antennas are good examples
whose shapes are completely described by angles. For the log periodic antennas, the entire
shape is not solely specified by angles rather it is also dependent on the length from the
origin to any point on the structure. However, the log periodic antennas can still exhibit
frequency independent characteristics. Fig. 1 illustrates the geometry of spiral, log periodic
and conical spiral antennas.
The second principle accounting for frequency independent characteristics is self-
complementarities, which was introduced by Mushiake in the 1940s derived from the
Babinet’s principle in optics. Mushiake discovered that the product of input impedances of a
planar electric current antenna (plate) and its corresponding “magnetic current” antenna
was the real constant 
2
/4, where  is the intrinsic impedance. Hence, if an antenna is its
own complement, the frequency independent impedance behavior is obtained. In Fig. 1 (a),
if the lengths W and S are the same, i.e., the metal and the air regions of the antenna are
equal; the spiral antenna is self-complementary. Fig. 1 (d) shows the geometry of a
logarithmic spiral antenna.
Although the frequency independent antennas can operate over an extremely wide
frequency range, they still have some limitations. Firstly, to satisfy Rumsey's requirement,
the antenna configuration needs to be infinite in principle but, in practice, it is usually
truncated in size. This requirement makes the frequency independent antennas quite large
in terms of wavelength. Secondly, the frequency independent antennas tend to be dispersive
because they radiate different frequency components from different parts of the antenna,
i.e., the smaller-scale part contributes higher frequencies while the large-scale part accounts
for lower frequencies. Consequently, the received signal suffers from severe ringing effects
and distortions. Due to this drawback, the frequency independent antennas can be used
only when the waveform dispersion may be tolerated.

(a) (b)

(c) (d)
Fig. 1. (a) Spiral antenna; (b) Log periodic antenna (SAS 510-7 from A.H. Systems Inc);
(c) Conical spiral antenna; (d) Logarithmic spiral antenna.

2.2.2 Multi-resonant antennas
Multi-resonant antennas are composed of an arrangement of multiple narrowband radiating
elements. This type of antenna includes log periodic antennas or Yagi antennas (Fig. 1(b)).
Planar versions of these antennas also exist. Although these antennas are UWB, yet they are
not convenient for IR-UWB systems because their phase centers are not fixed in frequency
and therefore exhibit dispersion.

2.2.3 Travelling wave antennas
Travelling wave antennas include horn antennas, tapered slot antennas and dielectric rod
antennas. These antennas feature a smooth and gradual transition between a guided wave
and a radiated wave, and have good properties for UWB.
Horn antennas constitute a major class of UWB directional antennas and these are
commonly used for measuring radiation patterns or for ground penetrating radar
applications. They consist of rectangular or circular waveguides which are inherently
broadband. Their bandwidth is relatively large, i.e., 50% - 180%. These antennas present
very good polarization, very low dispersion and very low variation in phase center versus
frequency. Fig. 2 (a) shows a double ridge horn antenna as an example.
The Tapered Slot Antenna (TSA) is another important class of UWB directional antennas. A
typical TSA consists of a tapered slot that has been etched in the metallization on a dielectric
substrate. The profile of tapering may take different forms: linear tapered slot antenna

(LTSA), constant width slot antenna (CWSA), broken linearly tapered slot antenna (BLTSA)
or exponentially tapered slot antenna (Vivaldi) as shown in Fig. 2 (b). The TSAs are adapted
to a wide bandwidth of 125% - 170%. Their radiation pattern is unidirectional in the plane of
the substrate and has a low level of cross-polarization. The directivity increases with
frequency and the gains achieved by these antennas can go up to 10 dBi depending on the
type of profile.

(a) (b)
Fig. 2. (a) Horn Antenna – SA S571 A.H. Sys. Inc; (b) Tapered slot antennas.

2.2.4 Small element antennas
Small-element antennas include Lodge’s biconical and bow-tie antennas, Mater’s diamond
dipole, Stohr’s spherical and ellipsoidal antennas, and Thomas’s circular dipole. These
antennas are direct evolution of monopole and the basic dipole (doublet of Hertz). Antenna
engineers discovered that, starting from a dipole or monopole antenna, thickening the arms
results in an increased bandwidth. Thus, for a thick dipole or monopole antenna, the current
distribution is no longer sinusoidal and where this phenomenon hardly affects the radiation
pattern of the antenna, there this strongly influences the input impedance too. This band-
widening effect is even more severe if the thick dipole takes the shape of a biconical antenna.
UWB antennas: design and modeling 377

The first one was introduced by Rumsey in the 1950s. Rumsey’s principle suggests that the
pattern properties of an antenna will be frequency independent if the antenna shape is
specified only in terms of angles. Infinite biconical and spiral antennas are good examples
whose shapes are completely described by angles. For the log periodic antennas, the entire
shape is not solely specified by angles rather it is also dependent on the length from the
origin to any point on the structure. However, the log periodic antennas can still exhibit
frequency independent characteristics. Fig. 1 illustrates the geometry of spiral, log periodic

and conical spiral antennas.
The second principle accounting for frequency independent characteristics is self-
complementarities, which was introduced by Mushiake in the 1940s derived from the
Babinet’s principle in optics. Mushiake discovered that the product of input impedances of a
planar electric current antenna (plate) and its corresponding “magnetic current” antenna
was the real constant 
2
/4, where  is the intrinsic impedance. Hence, if an antenna is its
own complement, the frequency independent impedance behavior is obtained. In Fig. 1 (a),
if the lengths W and S are the same, i.e., the metal and the air regions of the antenna are
equal; the spiral antenna is self-complementary. Fig. 1 (d) shows the geometry of a
logarithmic spiral antenna.
Although the frequency independent antennas can operate over an extremely wide
frequency range, they still have some limitations. Firstly, to satisfy Rumsey's requirement,
the antenna configuration needs to be infinite in principle but, in practice, it is usually
truncated in size. This requirement makes the frequency independent antennas quite large
in terms of wavelength. Secondly, the frequency independent antennas tend to be dispersive
because they radiate different frequency components from different parts of the antenna,
i.e., the smaller-scale part contributes higher frequencies while the large-scale part accounts
for lower frequencies. Consequently, the received signal suffers from severe ringing effects
and distortions. Due to this drawback, the frequency independent antennas can be used
only when the waveform dispersion may be tolerated.

(a) (b)

(c) (d)
Fig. 1. (a) Spiral antenna; (b) Log periodic antenna (SAS 510-7 from A.H. Systems Inc);

(c) Conical spiral antenna; (d) Logarithmic spiral antenna.

2.2.2 Multi-resonant antennas
Multi-resonant antennas are composed of an arrangement of multiple narrowband radiating
elements. This type of antenna includes log periodic antennas or Yagi antennas (Fig. 1(b)).
Planar versions of these antennas also exist. Although these antennas are UWB, yet they are
not convenient for IR-UWB systems because their phase centers are not fixed in frequency
and therefore exhibit dispersion.

2.2.3 Travelling wave antennas
Travelling wave antennas include horn antennas, tapered slot antennas and dielectric rod
antennas. These antennas feature a smooth and gradual transition between a guided wave
and a radiated wave, and have good properties for UWB.
Horn antennas constitute a major class of UWB directional antennas and these are
commonly used for measuring radiation patterns or for ground penetrating radar
applications. They consist of rectangular or circular waveguides which are inherently
broadband. Their bandwidth is relatively large, i.e., 50% - 180%. These antennas present
very good polarization, very low dispersion and very low variation in phase center versus
frequency. Fig. 2 (a) shows a double ridge horn antenna as an example.
The Tapered Slot Antenna (TSA) is another important class of UWB directional antennas. A
typical TSA consists of a tapered slot that has been etched in the metallization on a dielectric
substrate. The profile of tapering may take different forms: linear tapered slot antenna
(LTSA), constant width slot antenna (CWSA), broken linearly tapered slot antenna (BLTSA)
or exponentially tapered slot antenna (Vivaldi) as shown in Fig. 2 (b). The TSAs are adapted
to a wide bandwidth of 125% - 170%. Their radiation pattern is unidirectional in the plane of
the substrate and has a low level of cross-polarization. The directivity increases with
frequency and the gains achieved by these antennas can go up to 10 dBi depending on the
type of profile.

(a) (b)
Fig. 2. (a) Horn Antenna – SA S571 A.H. Sys. Inc; (b) Tapered slot antennas.

2.2.4 Small element antennas
Small-element antennas include Lodge’s biconical and bow-tie antennas, Mater’s diamond
dipole, Stohr’s spherical and ellipsoidal antennas, and Thomas’s circular dipole. These
antennas are direct evolution of monopole and the basic dipole (doublet of Hertz). Antenna
engineers discovered that, starting from a dipole or monopole antenna, thickening the arms
results in an increased bandwidth. Thus, for a thick dipole or monopole antenna, the current
distribution is no longer sinusoidal and where this phenomenon hardly affects the radiation
pattern of the antenna, there this strongly influences the input impedance too. This band-
widening effect is even more severe if the thick dipole takes the shape of a biconical antenna.

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