2014 IEEE International Microwave and RF Conference (IMaRC)

UWB Antenna with Reconfigurable Band-Notched Characteristics

using Ideal Switches
Sarah Jacob, S. Nimisha, P.V. Anila and P. Mohanan
Department of Electronics, Cochin University of Science and Technology, Cochin, Kerala, India.

Abstract — A CPW-fed band-notched Ultra wide band requires less space for implementation compared to the other
(UWB) antenna that functions as a UWB antenna/ band-notched designs using parasitic strips that are straight and have length
UWB antenna is proposed. The band-notched function at
WiMAX is obtained by etching S-shaped meandered parasitic comparable to the radiating aperture. The reconfigurable band-
element within the radiating aperture. Reconfigurability is notched characteristics are realized by ideal switches
verified by placing ideal switches across the gaps of the parasitic connected across the gaps of the S-shaped parasitic element.
element. Results show that the proposed antenna with For the proposed antenna, metallic strips are used as switching
reconfigurable band-notched characteristics operates from 2.5 to elements to confirm the effectiveness of the reconfigurability.
12 GHz.
Index Terms — Band-notched characteristics, Coplanar The design procedure and the measurement results are
waveguide fed antenna, Meandered Parasitic element, presented and discussed.
Reconfigurable antenna, Ultra wide band.
II. ANTENNA GEOMETRY AND DESIGN
I. INTRODUCTION
The geometry of proposed reconfigurable band-notched
Approval for the unlicensed band for UWB communication UWB antenna is shown in Fig.1. The antenna is fabricated on
applications in 2002 has stimulated research activities in a substrate with relative permittivity of 4.4, loss tangent of
antenna design between 3.1 to 10.6 GHz. Thereafter, many 0.02 and thickness of 1.6 mm.
different types of UWB antennas with dissimilar sizes and
shapes are proposed. Among these designs, the printed UWB
antenna has attracted significant attention due to its
compactness, satisfactory radiation properties, ease in
fabrication & integration with other RF circuits and low
manufacturing cost. To minimize the potential interferences
between UWB system and other co-existing narrowband
wireless services such as WiMAX (3.3 - 3.6 GHz), WLAN
(5.15 - 5.825 GHz) etc., it is desirable to design the UWB
antenna with band-notched functions.
A number of UWB antennas with band-notched
characteristics have been proposed, and the conventional
techniques for band-notched design include: cutting slots of
(a) (b)
different shapes on the radiating patch or in the ground plane
[1]-[2], placing parasitic elements [3] and attaching quarter Fig. 1. Geometry of the proposed reconfigurable band-notched
wavelength stubs into the ground plane or in the radiating UWB antenna (a) top view (b) side view
patch [4]. For designing a multipurpose UWB antenna which The antenna consists of a beveled rectangular patch and a
enables the antenna to operate as either UWB antenna or rectangular slotted ground plane. The required UWB
band-notched UWB antenna, reconfigurability becomes an bandwidth is obtained by including two major modifications
attractive method. Recently, several designs which use ideal on the slotted ground plane, (i) inserting slits (W 3 x L3) on the
switches (metallic strips) have been reported to demonstrate vertical strips of the slotted ground structure and (ii) beveling
the concept of switching [5]-[7]. the ground plane( αg) corners near the feed point. To achieve
In this paper, possibility of achieving reconfigurable band-notched performance at WiMAX, a S-shaped meandered
characteristics in a band-notched UWB monopole antenna is parasitic element is etched within the radiating aperture of the
verified. An S-shaped meander line parasitic element etched antenna. Then ideal switches are placed across the gaps of the
within in the radiating aperture of the antenna suppresses the S-shaped parasitic element to facilitate the reconfigurable
radiation at WiMAX band (3.3 - 3.6 GHz). The meandered band-notched characteristics. Here, ON state is represented by
structure is actually a microstrip line folded back and forth to the presence of a metallic strip which is shown by red
lower its resonant frequency with miniaturized size. Thus coloured square in Fig.1(a) and the OFF state by the absence

136 978-1-4799-6317-1/14/$31.00 ©2014 IEEE

of a metallic strip. By switching both SW1 and SW2 ON or Fig.3 illustrates the effect of horizontal strip length (ws) of
OFF, the proposed antenna can function as either a UWB S-shaped parasitic element on S11 characteristics of the
antenna or a band-notched UWB antenna respectively. antenna. It is observed that increase in ‘ws’ decreases the
The proposed reconfigurable antenna is simulated and notch frequency (WiMAX) because the inductance increases
optimized using CST Microwave Studio. The optimized as the length of the strip increases. Another important
parameters of the antenna are L x W x h = 30 mm x 27 mm x parameter of a meander line is the strip width (w); narrow
1.6 mm, L0 = 21.8 mm, W0 = 7mm , L1 = 4mm, W1 = 10 mm, strip offers high inductance which in turn lowers the notch
W2 = 4mm , L3 = 6.8 mm, W3 = 3 mm, L5 = 2.2mm, frequency again. Therefore, length of the strip required to
W5 = 11.65mm, αg = 16.7o, Wg = 8.8mm , Lr = 6mm, obtain a given notch frequency can be reduced by using
Wr = 5mm, Lf = 8.5mm, Wf = 3mm, ws = 10.8 mm, narrow strips, which provides a compact notch structure for
g = 0 .5 mm, s = 2 mm, w = 0.5 mm. WiMAX band.

(a)

Fig. 3. Effect of horizontal strip length of S-shaped parasitic

element on S11 of the band-notched antenna.

After exhaustive simulation studies with w = g, the length

of the horizontal strip is given by an empirical expression:

where λ1 is the free space wavelength at the designed notch

frequency f1 and

(b)
Therefore, the shifting of the rejection band can be achieved
Fig. 2. Simulated surface current distributions at notched by varying the parameter ‘ws’.
frequency (a) SW1 & SW2 are OFF (b) SW1 & SW2 are ON

Simulated surface current distributions at notched frequency III. RESULTS AND DISCUSSIONS
for both the cases are described in Fig.2(a) and (b). When
Both in simulation and fabrication, ideal switches (SW1 and
both SW1 and SW2 are OFF, the current is concentrated
SW2) are realized by thin metallic strips (0.6 mm x 0.5 mm).
mainly on the S-shaped parasitic element and flows in
When both the switches are ON the antenna behaves as a
opposite directions in the adjacent horizontal strips as in
UWB antenna operates from 2.5 GHz to 12 GHz. When both
Fig.2(a). Hence results in minimized radiations at that
the switches are OFF the antenna exhibits a band-notched
frequency. For the other case when both the switches are ON,
characteristic with notch frequency at 3.4 GHz. i.e., a
current is not present on the parasitic element. The current
reconfigurable band-notched characteristic is obtained. The
flows mainly on the antenna structure thus functions as UWB
simulated and measured switching characteristics of the
antenna with bandwidth from 2.5 to 12 GHz.

137
proposed reconfigurable antenna are described in Fig.4. The
measured results agree well with simulated results as
expected.

Fig. 6. Simulated and measured peak gain of the proposed

antenna when both the switches are OFF and ON

Since UWB antenna is often used in pulse communication,

Fig. 4. Simulated and measured S11 of the proposed antenna the time domain performance of the antenna is also to be
when both the switches are OFF and ON considered. In order to study the time domain impulse
response of the proposed antenna using CST, a fourth-order
The measured radiation patterns of the antenna with both
Rayleigh pulse is used as the source pulse. Fig.7 and Fig.8
switches OFF at 2.8 GHz, 6.5 GHz and 10.6 GHz are shown
show the antenna transfer function and the radiated pulses
in Fig.5(a) and (b), which illustrates that the antenna can
with both switches ON and OFF taken by virtual probe
provide a nearly omnidirectional pattern in H-plane and
oriented for face to face direction in H-plane.
‘figure of eight’ pattern in E-plane over the entire bandwidth.

(a) (b)

Fig. 5. Measured radiation patterns of the antenna (a) H-plane

and (b) E-plane when both the switches are OFF
Fig. 7. Normalized magnitude of the antenna transfer function in
The peak gain of the antennas with both the switches ON H-plane with both the switches OFF and ON
and OFF are measured by gain comparison method. Stable
gain responses have been achieved except at the notched band.
The antenna transfer function is a measure of dispersion
A sharp decrease in gain is observed in the vicinity of 3.4 GHz
behaviour of UWB antenna; it should be flat in the operating
as shown in Fig.6.
band except in the notched bands and should drop drastically
outside the operating band. Fig.7 ensures these criteria for the
proposed antenna. In Fig.8, the source pulse and the radiated
pulses are plotted and shifted along the time axis to display
clearly. It is observed that the radiated pulses in both the cases
are nearly same as source pulse which reveals that the

138
proposed reconfigurable antenna does not distort the pulse at Transactions on Antennas and Propagation, vol. 62, no. 1, pp.
all, i.e., it is suitable for UWB pulse communication. 490-494, 2014.
[5] M. R. Hamid, P. S. Hall, P. Gardner, and F. Ghanem, “Switched
WLAN-wideband tapered slot antenna,” Electronic Letters, vol.
46, pp. 23–24, 2010.
[6] B. Li, J. Hong and B. Wang, “Switched band-notched
UWB/dual-band WLAN slot antenna with inverted S-shaped
slots”, IEEE Antennas and Wireless Propagation Letters, vol.
11, pp. 572-575, 2012.
[7] Y. Li, W. Li and Q. Ye, “A compact circular slot UWB antenna
with multimode reconfigurable band-notched characteristics
using resonator and switch techniques”, Microwave Optical &
Technology Letters, vol. 56, no. 3, pp. 570-574, 2014.

Fig. 8. Normalised source pulse and radiated pulses with both the
switches OFF and ON

IV. CONCLUSION
A band-notched UWB antenna which can redesign as a
reconfigurable antenna is presented. The band-notched
performance is obtained by etching a S-shaped meandered
parasitic element and the reconfigurable characteristics are
confirmed by placing two ideal switches (metallic strips)
across the gaps of the S-shaped parasitic element. By
controlling the ON and OFF status of the switches, the
proposed antenna can function either as UWB antenna with a
bandwidth of 126% or as a band-notched UWB antenna.
Measured and simulated results prove that the proposed
antenna is suitable for multipurpose wireless pulse
communication applications.

ACKNOWLEDGEMENT
The authors acknowledge Department of Science &
Technology (DST) and University Grant Commission (UGC),
Govt. of India for the financial support.

REFERENCES
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