UWB dual band notch Antenna

1. 872 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 13, 2014
Compact Bluetooth/UWB Dual-Band Planar Antenna
With Quadruple Band-Notch Characteristics
G Shrikanth Reddy, Student Member, IEEE, Anil Kamma, Sanjeev. K. Mishra, Member, IEEE, and
Jayanta Mukherjee, Senior Member, IEEE
Abstract—A compact Bluetooth/Ultrawideband (UWB) dual-
band planar antenna with quadruple band-notch characteristics
is presented. The proposed structure consists of a UWB semi-el-
liptical planar monopole, attached to an approximate trapezoidal
spiral for 2.45-GHz Bluetooth application. The proposed antenna
utilizes rectangular resonant spiral structures for rejection of
quadruple frequency bands, i.e., WiMAX (3.3–3.6 GHz), WLAN
(5.15–5.35, 5.725–5.825 GHz), and ITU 8 GHz. These resonant
spirals are capacitively coupled with the microstrip feedline.
The band-notch characteristics are controlled by changing the
effective length of the spirals along with coupling gaps between the
feedline and the spirals. The proposed antenna also achieves sharp
reduction in the gain and efficiency at all the notch frequencies.
However , at the passbands, the gain and radiation efficiency
are almost stable. A good agreement between the simulated and
measured results shows that the proposed antenna with sur-
face dimensions of 24 17 mm is suitable for Bluetooth/UWB
dual-band applications.
Index Terms—Bluetooth, capacitively coupled spiral, quadruple
band-notch, stepped ground plane, ultrawideband antenna.
I. INTRODUCTION
WITH the allocation of 3.1–10.6-GHz band for ultra-
wideband (UWB) applications by the Federal Com-
munications Commission (FCC) [1], a considerable amount of
interest is focused in UWB technologies. Despite advantages
like ultra-wide unlicensed bandwidth, high data rate, compact
system, etc., UWB technology faces many implementation
challenges. One of the major challenges is to avoid interference
due to coexisting narrow microwave frequency bands, i.e.,
IEEE 802.16 WiMAX band (3.3–3.6 GHz), IEEE 802.11a
WLAN bands (5.15–5.35, 5.725–5.825 GHz), and ITU 8-GHz
band (8.025–8.4 GHz). To reduce interference from these
frequency bands, bandpass filters can be utilized, but this will
increase the cost and overall system size. Thus, a compact UWB
antenna with multiband rejection characteristics is desirable.
For realizing UWB antennas with band-notch character-
istics, several methods have been proposed [2]–[11]. Most
common among these methods are slot techniques [2]–[5].
Manuscript received December 18, 2013; revised January 18, 2014 and
March 21, 2014; accepted April 25, 2014. Date of publication April 29, 2014;
date of current version May 09, 2014.
G. S. Reddy, A. Kamma, and J. Mukherjee are with the Department of Elec-
trical Engineering, Indian Institute of Technology Bombay, Mumbai 400076,
India (e-mail: shri@ee.iitb.ac.in; anilkamma@ee.iitb.ac.in; jayanta@ee.iitb.ac.
in).
S. K. Mishra is with the Department of Avionics, Indian Institute
of Space Science and Technology, Trivandrum 695547, India (e-mail:
sanjeevkmishra@iist.ac.in).
Color versions of one or more of the figures in this letter are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LAWP.2014.2320892
Slot techniques involve etching of quarter-wavelength or
half-wavelength differently shaped slots in the antenna or in the
ground plane such as U-shaped slot, complementary split-ring
resonators (CSRRs), etc.
Slot techniques are very effective in producing band notches.
However, they can produce single- or dual band-notches only.
For multiple band-notch characteristics, multiple slots can be
used [4], [5], but multiple slots affect the antenna’s gain and
efficiency. Recently, in [6]–[8], parasitic coupled resonators/
loops are used for achieving multiple band-notch characteris-
tics. These loops are capacitively or inductively coupled with
the feedline, and their effective length determines the notch
bandwidth. However, these loop-based structures have certain
limitations such as limited compactness, limitations in sharp
cutoff especially for WLAN bands, and mutual coupling be-
tween loop elements. In order to utilize the advantages of loop
resonators, they should be designed precisely such that their
effective lengths are in proximity to the wavelengths of notch
frequencies. Coupling distance between loop elements and the
feedline also plays a major role in deciding the nature of notch
bandwidth.
In addition to multiple band-notch UWB characteristics, it
is desirable to have the antenna work for Bluetooth band. The
structures presented in [9]–[14] provide the impedance band-
width ( ) covering multiple frequency bands along
with the UWB bandwidth. The antenna proposed in this letter
is realized in two stages. In the first stage, a modified trape-
zoid-shaped spiral is mounted on the semi-elliptical printed
monopole to achieve Bluetooth/UWB dual-band characteris-
tics. In the second stage, quadruple band-notch characteristics
are realized by capacitively coupling rectangular spirals of
different effective lengths with the feedline of a dual-band
antenna.
Performance of the proposed antenna is tested both theoret-
ically using CST Microwave Studio simulator and experimen-
tally. A good agreement between simulated and measured re-
sults ensures the suitability of the proposed antenna for dual-
band operation with quadruple band-notch characteristics.
II. BLUETOOTH/UWB DUAL-BAND ANTENNA WITHOUT AND
WITH BAND-NOTCH CHARACTERISTIC
A. Dual-Band Antenna Configuration (Stage 1)
Geometry of the proposed semi-elliptical printed monopole
(base) antenna is shown in Fig. 1(a). The antenna is designed
on 24 17 0.787-mm Duriod substrate with
and . It is fed by a 50- microstrip line. This
monopole is designed for 3.5 GHz as its lower frequency bound,
using the monopole design techniques mentioned in [14]. Its
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2. REDDY et al.: COMPACT BLUETOOTH/UWB DUAL-BAND PLANAR ANTENNA WITH QUADRUPLE BAND-NOTCH CHARACTERISTICS 873
Fig. 1. Configurations of base structure. (a) Base semi-elliptical antenna.
(b) Base antenna mounted with regular spiral.
Fig. 2. Optimization for Bluetooth bandwidth (all dimensions are in
millimeters).
lower frequency is lowered to 3 GHz using a stepped ground
plane with the slot at the upper edge of ground plane
(for UWB impedance matching). For dual-band characteristic,
a nearly trapezoidal spiral structure is proposed. Spirals are
self-resonating structures, whose resonance frequency depends
on the length of its inductive arms and capacitive gaps between
the arms. For proper resonance, it is necessary that effective
length of the spiral should be in proximity to the wavelength
corresponding to the resonant frequency. Initially, for Bluetooth
band, a regular spiral is designed with resonant frequency of
2.45 GHz.
As shown in Fig. 1(b), the dimensions of regular spiral such as
number of turns, , , and are calculated and optimized
using the techniques given in [15]
(1)
Here, is the number of turns and is the total effective
length of the spiral that is approximated as
(2)
In (2), is speed of light in free space, is the effective di-
electric constant, is the guided wavelength, and is taken
as 2.45 GHz. For finalizing number of turns, values of and
were fixed to 0.5 mm. It is observed from (1) and (2) that with
increase in , number of turns will also increase. Since the
required is 22.69 mm, can be approximated to 6 mm
with corresponding . The optimized
values of and are 1.25 and 29 mm, respectively. The
differences in theoretically calculated and optimized values of
and are due to the fact that theoretical calculations are
based on analysis of individual spiral structure, whereas final
values are optimized after mounting the spiral on the semi-ellip-
tical monopole. To achieve desired dual-band characteristic for
Fig. 3. Realization of an approximate trapezoidal spiral for achieving Blue-
tooth frequency band (all dimensions are in millimeters).
Fig. 4. (a) Surface current distribution at 2.45 GHz. (b) VSWR characteristic.
Bluetooth and UWB operations, all dimensional parameters are
optimized. The optimization of Bluetooth bandwidth at different
positions of is as shown in Fig. 2. Other optimized dimensions
are as follows: , , , , ,
, , , , ,
, , , , (all dimensions are
in millimeters). After optimizing Bluetooth bandwidth, surface
area of the mounted spiral is further reduced by replacing it with
a trapezoidal equivalent, as shown in Fig. 3. The value of bend
angle after optimization is found to be 56.25 . To compen-
sate for the reduction in effective length, number of turns in the
trapezoidal spiral is further increased with similar bend angles.
It can be seen in Fig. 3 that the line and gap widths in the
spiral, especially at the corners, are more compared to other
sides. In order to maintain a uniform gap between strips of the
spiral, these corners are not chamfered. The optimized effective
length of the trapezoidal spiral ( ) is 30 mm. It can be seen
in Fig. 3 that by introducing the nearly trapezoidal spiral, sur-
face area of the Bluetooth resonator is reduced by nearly 35%
compared to the regular spiral.
The surface currents distribution in Fig. 4(a) shows the
resonant behavior of the proposed structure. It can be seen
in Fig. 4(b) that antenna C exhibits an impedance bandwidth
( ) of 2.4–2.6 GHz along with UWB bandwidth,
which is similar to antenna B. Antenna C is fabricated (printed)
on RT Duriod 5880 substrate with , ,
and thickness of 0.787 mm. The measured and simulated
results shown in Fig. 4(b) validate the dual-band characteristic
of antenna C.
B. Quadruple Band-Notch Antenna (Stage 2)
For addressing interference from coexisting microwave fre-
quency bands, resonant spiral structures , , and are
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3. 874 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 13, 2014
Fig. 5. Proposed antenna with capacitively coupled spiral structures. (a) Front
view. (b) Back view (all dimensions are in millimeters).
Fig. 6. Optimization of notch bandwidths with respect to coupling distances
(all dimensions are in millimeters): (a) considering only ; (b) considering
only ; (c) considering only .
capacitively coupled with the feedline of the base antenna as
shown in Fig. 5.
Here, spirals , , and are designed to reject WiMAX
and WLAN bands. The effective lengths ( , , and ) of
rectangular spirals are chosen as instead of . Here,
is guided wavelength corresponding to the center frequency of
the desired notch bands. The reason for using effective lengths
as is to reduce the fabrication complexities. Other dimen-
sions such as the number of turns, strip width, gap between the
turns, and distance between two consecutive spirals are opti-
mized for achieving sharp cutoff in the notch band with low mu-
tual coupling between consecutive spiral structures. Optimiza-
tions of coupling distances (considering one spiral at a time) are
shown in Fig. 6.
Fig. 7. Surface current distribution at (a) 3.45, (b) 5.215, (c) 5.77, and
(d) 8.195 GHz. (e) Current cancellation behavior at 5.77 GHz.
TABLE I
DIMENSIONAL VALUES OF BAND-NOTCH SPIRALS
As depicted in Fig. 6(a), spiral provides band notch for
WiMAX and ITU 8-GHz bands. The reason for this dual band-
notch behavior is the effective length of . The effective length
of ( ) is not only for WiMAX band, but approxi-
mately equivalent to for 8.195 GHz. This provides the
dual resonant behavior, i.e., one for WiMAX band and another
for 8.195-GHz band. The optimized dimensional values of ,
, and are tabulated in Table I.
In order to avoid mutual coupling between and , gap
is kept at 0.5 mm. Fig. 7 shows surface current distribution along
the rectangular spirals at their respective resonant frequencies.
It can be seen that for all notch frequencies, the concentration of
surface currents is more along the rectangular spirals. Due to the
opposite phase of surface currents at , , and , it cancels
out the currents along the feedline and ground plane as shown
for 5.77 GHz in Fig. 7(e). Similar cancellation is observed for
all rectangular spirals at their respective notch frequencies.
Based on simulated results, the proposed structure is
fabricated and tested to validate its quadruple band-notch
characteristics. Total surface area of the fabricated prototype
is 24 17 mm . Fig. 8 shows the measured VSWR char-
acteristic of the proposed antenna. It can be seen that both
measured and simulated VSWR characteristics indicate band
notch ( ) at 3.3–3.65, 5.12–5.3, 5.72–5.83, and
8.018–8.4 GHz. These results show the sharp band-notch
nature of the proposed rectangular spiral structure.
The gain and efficiency responses shown in Fig. 9 also
validate the quadruple band-notch behavior of the proposed
antenna. It is observed that for passbands, the proposed antenna
exhibits a nearly stable gain response with an average of 3 dBi
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4. REDDY et al.: COMPACT BLUETOOTH/UWB DUAL-BAND PLANAR ANTENNA WITH QUADRUPLE BAND-NOTCH CHARACTERISTICS 875
Fig. 8. VSWR characteristic of proposed antenna with fabricated prototype (as
per Fig. 5).
Fig. 9. Measured gain and antenna efficiency response.
Fig. 10. Measured radiation pattern of proposed antenna (magnitude in
decibels).
Fig. 11. Measured group delay response between identical proposed antennas
kept 60 cm apart (in two orientations).
for Bluetooth and 5.5 dBi for UWB bands. The average effi-
ciency of the proposed antenna for both Bluetooth and UWB
bands is above 80%, which is due to the absence of slots,
whereas at notch frequencies it is as low as 20%.
The measured radiation patterns of the proposed antenna
are shown in Fig. 10. It is observed that for both Bluetooth
and UWB bandwidths, radiation patterns are nearly stable,
being bidirectional in the -plane and omnidirectional in
the -plane. For the proposed antenna, both simulated and
measured results show that compared to [9]–[13], the proposed
antenna is more compact and provides sharp cutoffs for the
notch bands with stable gain and radiation characteristics.
To ensure stable transmission characteristic, group delay with
small variations and fidelity factor nearly equal to 1 are required.
The group delay response shown in Fig. 11 shows a stable delay
with variations within 1 ns throughout the desired frequency
band. Fidelity factor for the proposed antenna is also analyzed
using techniques given in [16]. It is observed that for all the ori-
entation angles in -plane, fidelity factor is within the 0.87–0.9
range. These results indicate stable transmission characteristic
of the proposed antenna.
III. CONCLUSION
A compact Bluetooth/UWB dual-band planar antenna with
quadruple band-notch characteristics is presented. The resonant
behavior of the trapezoidal spiral for Bluetooth band and rect-
angular spirals for quadruple band notch is validated through
simulated and measured results. VSWR, gain, and efficiency
response depict dual-passband and quadruple-notch behavior of
the proposed antenna. Stable radiation pattern with antenna gain
between 4–5.8 dBi and variations of group delay within 1 ns (for
passbands) ensures that the proposed antenna can be utilized for
various Bluetooth/UWB applications with high immunity from
electromagnetic interference.
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