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Design of a Dual Band-notched Ultra-wideband
Antenna using CSRR and Modified Mushroom-type
EBG structure
Debdeep Sarkar#1, Saptarshi Ghosh#2, Somak Bhattacharyya#3, Kumar Vaibhav Sriavstava#4
#Department of Electrical Engineering, Indian Institute of Technology
Kanpur-208016, India
Tel. No.: +91-512-2597733, Fax No.: +91-512-2590063
1debdeep1989@gmail.com, 2joysaptarshi@gmail.com, 3bhattacharyya.somak@gmail.com, 4kvs@iitk.ac.in
Abstract— This paper presents a novel ultra-wideband (UWB)
planar monopole antenna with dual-band notched characteristics
achieved by embedding sub-wavelength meta-resonators
(Complementary Split Ring Resonators and modified mushroom
EBG elements) in the antenna structure. The proposed antenna
structure is simulated in HFSS and it shows wide impedance
bandwidth (VSWR < 2) covering the FCC specified UWB range
(3.1-10.6 GHz), with satisfactory rejection in the desired
frequency bands of IEEE 802.11a / HIPERLAN-2 and X-band
communication along with good average gain (>3 dBi) and stable
monopole-like radiation pattern in the other parts of the UWB
regime.
Keywords- Ultra-wideband (UWB), Planar Monopole Antenna,
Electromagnetic Interference (EMI), Band-notched Characteristics,
Complementary Split Ring Resonator (CSRR), Modified
Mushroom Electromagnetic Band-gap (EBG) Structure.
I. INTRODUCTION
Ultra-wideband (UWB) systems, operating in the frequency
range 3.1-10.6 GHz as allocated by FCC [1], have become
very popular in short-range communication technology for
features like extremely high data rates and low power
consumption. Different UWB antenna topologies have been
proposed [2-4] to meet up with the design criteria of high
impedance-bandwidth, stability of radiation pattern,
miniaturization and low manufacturing cost. Prevention of
electromagnetic interference (EMI) caused by narrowband
communication systems like WiMAX, WLAN (IEEE 802.11a,
HIPERLAN-2) and X-band satellite communication systems
has always been a challenge for UWB antenna designers.
The use of external band-stop filters integrated with the
antenna increases the footprint of the antenna considerably; so
researchers have resorted to an approach of embedding slots
of different shapes [5-6] or complementary split ring
resonators (CSRRs) [7] in the antenna radiator or ground
plane. These slots provide intrinsic band-stop filtering by their
inherent resonance mechanism. Moreover, providing more
than one notch-bands in the UWB antenna characteristics is
necessary for many applications; so mutually non-interacting
band-stop elements must be implanted in the antenna structure.
This paper presents the design of a dual band-notched
circular UWB patch antenna (Fig. 1), where strong notch-
characteristics in the 5.15-5.85 GHz band is achieved by
placing a modified mushroom unit cell generally used in
Fig. 1: Top-view of the proposed Dual-Band Notched UWB Antenna.
electromagnetic band-gap surface design. Furthermore, by
etching out a CSRR near the junction of microstrip feeding
section and the radiating patch, the 7.9-8.4 GHz frequency
band used for X-band communication system is also rejected.
Both the band-reject elements (CSRR and the modified
mushroom unit cell) operate in the sub-wavelength regime
(dimensions < λ/6). The proposed antenna also provides
monopolar far-field radiation pattern in the radiating band.
The paper is organized as follows. Section-II illustrates the
design of the reference circular UWB patch antenna. The
implementation methodology and characteristics of the
proposed antenna, along with its comparison with the
reference antenna, is presented in section-III.
II. DESIGN OF REFERENCE UWB ANTENNA
The reference UWB antenna is a low-profile (single-layer)
microstripline-fed antenna, designed on 0.787 mm thick
Rogers RT/Duroid 5880 substrate (εr = 2.2, tanδ = 0.0009)
having surface area 32 mm x 40 mm. The radiating element is
a circular patch (Fig. 1) having radius Rpatch, placed near a
partial ground plane of width Wgand length Lg. The feed-
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structure is fed by a 50 ohm microstripline (width Wfand
length Lf), followed by an impedance matching section (width
Waand length La) [3]. The antenna structure is simulated as
well as optimized by FEM-based commercial electromagnetic
simulator HFSS to achieve a good impedance bandwidth
matching (VSWR < 2) over the UWB frequency range (3.1-
10.6 GHz) along with good far-field gain. The antenna
parameters used for final simulation are listed in Table I.
TABLE I
DESIGN PARAMETERS OF THE REFERENCE ANTENNA
Parameter
-
symb
ol
Dimension (mm)
R
patch
7.76
W
f
2.48
L
f
13.30
W
g
31.17
L
g
18.00
W
a
1.50
L
a
5.00
III. PROPOSED DUAL-BAND NOTCHED CIRCULAR PATCH
ANTENNA:RESULTS AND COMPARISON
To provide the band-notch at the WLAN frequencies (5.15-
5.85 GHz), the modified mushroom unit cell [8] as shown in
Fig. 2(a) is kept in the vicinity of the original patch antenna.
This element is basically a CSRR-loaded conventional
mushroom unit cell which is generally used in constructing
electromagnetic bandgap surfaces [9]. By performing two-port
analysis technique as employed in [10] and parametric
optimization of this unit cell in HFSS, its dimension and
positioning with respect to the reference antenna are tuned in
order to generate the desired band-rejection.
Similarly following the methodology in [11], the design
parameters of the CSRR etched on the radiating patch as
shown in Fig. 2(b) are also adjusted in order to have band-
notch in the upper band for X-band communication. Table II
and III show the final design parameters of the unit cells used
for dual band-notched UWB antenna design.
TABLE- II
DESIGN PARAMETERS OF THE MODIFIED MUSHROOM UNIT CELL
Parameter-symbol Dimension (mm)
W
1
4.50
W
2
4.00
S
1
0.30
S
2
0.30
S
3
0.40
S
4
0.50
G
2
0.30
D
via
0.40
sepx
0.40
sepz 0.40
TABLE III
DESIGN PARAMETERS OF THE CSRR
Parameter-symbol Dimension (mm)
g0.40
d0.30
c0.40
a4.50
b3.50
(a)
(b)
Fig. 2: (a) Dimensions of Modified Mushroom EBG unit cell (a)
Dimensions of CSRR.
Fig. 3 shows the comparison of the plots of VSWR versus
frequency for four different cases:
A. Reference Antenna
B. Antenna only loaded with modified mushroom unit
cell
C. Antenna only loaded with CSRR
D. Proposed antenna: loaded with two band-notch
elements
It is evident that the proposed antenna has an impedance
bandwidth of 2.93-10.97 GHz encompassing the entire UWB
spectrum along with desired band-notch in the bands 5.18-
5.77 GHz and 7.92-8.7 GHz, which helps to cancel
interference effects due to existing WLAN and X-band
communication systems. The maximum VSWR values
achieved in the two bands (at 5.32 GHz and 8.11 GHz
respectively) are quite high (> 10), which implies very strong
rejection.
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Fig. 3: VSWR versus frequency plots of the proposed antenna and the
reference antenna.
Fig. 4 illustrates the variation of peak realized far-field
gain of the proposed antenna along with that of the reference
antenna over the entire UWB range. Significant dip is
observed in the non-radiating bands (peak-gain < 0 dBi),
along with satisfactory average gain (peak-gain > 2.5 dBi)
over the rest of the frequencies where VSWR is less than 2. At
frequencies 5.32 GHz and 8.11 GHz, where the VSWR
achieves maximum value, the obtained values of peak realized
gain are -5.679 dBi and -0.753 dBi respectively.
Fig. 4: Plot of Maximum Far-field realized gain with frequency for the
proposed and reference antenna.
For the radiating band of the proposed dual-band notched
antenna, the far-field radiation pattern is nearly monopolar as
shown in Fig. 5. Fig. 6 shows the E-plane and H-plane
patterns of the proposed antenna at 7 GHz which is
approximately the centre frequency of the UWB range.
Fig. 5: 3D pattern of realized gain for 7 GHz.
(a)
(b)
Fig. 6: (a) E-plane (yz plane) and (b) H-plane (xy plane) patterns of the
proposed antenna at 7 GHz.
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To have insight to the electromagnetic phenomena behind
the dual-band rejection, the magnitude plot of the surface
current over the radiating patch and modified mushroom unit
cell for three frequencies 5.32 GHz, 7 GHz and 8.11 GHz are
shown in Fig. 7. Strong concentration of surface current is
observed in the band-reject elements, modified mushroom unit
cell and CSRR, at the notch frequencies 5.32 GHz and 8.11
GHz respectively. On the other hand, presence of significant
current distribution near radiating edges of the antenna is
observed at 7 GHz, where the antenna exhibits monopolar
radiation characteristics.
Fig. 7: Magnitude of surface current distribution for three different
frequencies.
IV. CONCLUSION
A dual band-notched circular patch antenna having UWB
characteristics with notch-bands in the WLAN (5.15-5.85
GHz) and X-band communication (7.9-8.4 GHz) frequency
ranges has been designed. The impedance bandwidth
characteristics and far-field radiation pattern of the antenna
are analyzed by HFSS simulations. The results are also well
supported by current distribution in the structure.
The proposed antenna employs single layer and low
cost RT/Duroid 5880 substrate. The antenna would be
fabricated and tested in near future to validate the simulation
results. The design methodology of this paper can be extended
to implement UWB antennas with multiple band-notch
properties.
ACKNOWLEDGMENT
The authors would like to acknowledge all the members of
the Microwave circuit and Microwave Metamaterials
Laboratory (Department of Electrical Engineering, IIT Kanpur)
for their inspiration and IIT Kanpur authority for the financial
assistance.
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