2014 Fifth International Conference on Intelligent Systems, Modelling and Simulation
Low-profile Inverted A-Shaped Patch Antenna for Multi-band Operations
Md. Rezwanul Ahsan, Mohammad Habib Ullah, Mohammad Tariqul Islam, Norbahiah Misran
Department of Electrical, Electronic and System Engineering,
Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia
43600 UKM, Bangi, Selangor, Malaysia
e-mail: [email protected]
An extensive research efforts have been contributed by
the researchers in the augmentation of patch antenna
performances by integrating various technologies to make it
small and operate in several discrete frequencies while
ensuring overall steady performance. Despite design
complexities associated with multiband antenna, many
researchers have discussed the designing process of patch
antenna which can operate more than one frequency. A
number of studies accompanying the applications and
techniques have reported in designing multiband antenna;
making tapered structure with coplanar waveguide (CPW)
fed [11], configuring slots over the radiating patch [12],
introducing capacitive coupled patch [13], utilizing high
dielectric substrate [14], integrating electromagnetic band
gap (EBG) structure [15, 16] and proposing metamaterials
[17]. In recent times, the Worldwide interoperability for
Microwave Access (WiMAX) operate at 2.5/3.5/5.5 GHz
bands is becoming very popular due to its strategic features
[11]. Whereas, microwave C-bands operating at 4 to 8 GHz
has advantages over the Ku-band and the developing regions
in Africa, Asia see a promising expansion of C band satellite
applications in near future [18, 19].
Through reviewing a number of articles it has been found
that numerous studies have performed in the design of
multiband patch antenna. The planar monopole antennas like
[20, 21] are reported as operating with broad bandwidth, but
their overall dimension 250x250 mm2 is large enough and
does not comply with miniaturization requirements for RF
devices [22]. A double G-shaped planar multiband antenna
of 40x30 mm2 has been designed for WLAN, WiMAX,
HIPERLAN2 [5]. A 50x50 mm2 slot ring antenna integrated
with capacitive patch has been proposed which is able to
function at frequencies related to WLAN and WiMAX
applications [13]. Coplanar Waveguide (CPW)-fed slotted
patch antennas of 23x30 mm2 to operate in 2.4-2.63 GHz,
3.23-3.8 GHz and 5.15-5.98 GHz bands [23], and 25x25
mm2 to cover 2.14-2.85 GHz, 3.29-4.08 GHz, and 5.02–6.09
GHz bands [11] have been developed. Two-U slot shaped
patch antenna of 40x50 mm2 with three resonant frequencies
2.7 GHz, 3.3 GHz and 5.3 GHz has been implemented to
cover tri-band wireless system [24]. In all afore mentioned
proposals and designs, the main target of the researchers is to
achieve multiband antenna by compromising either
fabrication cost or effective electrical area of the patch or
steady radiation performance or gain or efficiency. The
researchers may not have proper concentration on overall
Abstract—A low-profile modified inverted-A shape patch
antenna for multi-band operations is designed, fabricated and
analyzed. The proposed antenna has 20x20 mm2 radiating
patch fed by 4 mm long microstrip line on 1.6 mm thick
fiberglass polymer resin dielectric material substrate and a
reduced ground plane. The proposed antenna is designed and
simulated by using market available 3-dimensional high
frequency electromagnetic simulator HFSS and the antenna
properties are measured in a standard far field anechoic
chamber. The measurement results shows that impedance
bandwidths (return loss<-10dB) are of 360 MHz (2.53-2.89
GHz) and 440 MHz (3.47-3.91 GHz) for WiMAX, and 1550
MHz (6.28-7.83 GHz) for C-band satellite applications. The
maximum measured gain of 3.62 dBi, 3.67 dBi and 5.7 dBi are
obtained at lower, middle and upper band respectively. The
analysis results show almost stable radiation patterns and high
efficiencies for the proposed antenna in all bands of interest.
Keywords-microstrip antenna, multiband application,
fiberglass polymer resin, anechoic chamber, WiMAX, C-band.
I.
INTRODUCTION
The modern technological advancement and emerging
trends in the area of wireless communications raise
considerable research interest in antenna designs. To comply
with the contemporary technological improvements, it is
required to easily integrate the antenna with various systems
by ensuring minimal physical profile with multi functionality
in a single device. Moreover, the recent progress and
versatile use of personal communications and portable
devices necessitate the mandatory use of low-cost,
lightweight, compact, multi-frequency antenna. Printed
microstrip patch antennas are competitive solution for its
inherent advantages of low-cost, low-profile, lightweight,
less troublesome fabrication and ease of integration to the
system [1]. In general, the antenna performance and its
dimension are essentially interlinked together; an antenna
performance is said to be good when its resonance and size is
analogous to the wavelength. To deal with the current and
future mobile communications, wireless services and satellite
applications, a multiband/multifunctional microstrip patch
antenna associated with high-performance and good
radiation characteristics are certainly required [2–6].
Furthermore, The growing interest of antenna technology for
portable devices leads the way for extensive use as wireless
component in societal daily life which raises the concerns
surrounding its harmful radiation [7–10].
2166-0662/14 $31.00 © 2014 IEEE
DOI 10.1109/ISMS.2014.126
700
antenna dimension while paying their effort in improving
other criteria of antenna performances. In spite of everything,
opportunities are ahead to research for designing low profile
patch antenna with high gain, good radiation characteristics
and high efficiency.
Based on the background of the researches above, this
paper proposes a simple and small form factor
multifunctional patch antenna fabricated on low cost, durable
fiberglass polymer resin material substrate. The modified
inverted-A shaped multiband patch antenna of 20x20 mm2
has been designed, fabricated and its performance criteria
has been critically analyzed by comparing other similar
work.
II.
DESIGNING ANTENNA MODULE
The geometrical structure and configuration with detailed
design parameters of the proposed inverted-A shaped patch
antenna is shown in Fig. 1, which is designed and fabricated
on a 1.6 mm thick fiber glass polymer resin (FR4) substrate
with relative dielectric constant εr = 4.6 and loss tangent tan
δ = 0.02. The industry standard, 3D full wave
electromagnetic field simulation tool HFSS package is used
for the design and simulation of the proposed inverted-A
shape antenna and in house LPKF PCB prototyping machine
is used for the fabrication process. The two sided structure of
the antenna which consists of standard 50Ω SMA connector,
a microstrip line for feed, modified inverted-A shaped
radiating patch on top and a reduced rectangular ground
plane. The inverted-A shaped antenna structure is achieved
by cutting slots from a conventional rectangular patch. The
analytical study shows that the width of the patch has
insignificant effect on obtaining resonance and through
mathematical modeling the patch width for desired
frequency can be calculated [12]. The dimension of the
microstrip line is optimized through design and simulation to
obtain enhanced impedance matching over the operating
frequency bands. The designing process of the antenna is
started with the estimating the overall dimension of radiating
patch which is chosen to be of inverted-A shape that is
responsible for providing compact size of the antenna.
The overall size of the patch is of 20 x 20 mm2 (W x L)
where the complete dimensions are (in mm) presented in
Table I. To obtain the optimized geometric inverted-A shape,
numerous simulations and analysis have been performed
using HFSS. The effective length of the radiating patch and
cutting slots in different location on the patch controls the
lower band frequencies whereas, location of feed and strip
line characteristics generally responsible for high frequency
bands. Fig. 2 represents the photograph of the fabricated
modified inverted A shape slotted patch antenna.
TABLE I.
Figure 1. Geometrical structure of the proposed antenna
Figure 2. Photograph of the fabricated proposed antenna
III.
After successful completion of the design aspects, a
fabrication prototype has been constructed and measured.
The Agilent’s Vector Network Analyzer is use for measuring
the antenna parameters in a standard far-field anechoic
measurement chamber. The measured and simulated
reflection coefficients (return loss) versus frequency of the
proposed antenna is presented in Fig. 3. It is readily apparent
from the figure that that an excellent agreement has been
attained between simulated and measured results. Three
distinct impedance bandwidths with 10 dB return loss are
achieved: 360 MHz from 2.53–2.89 GHz, 440 MHz from
3.47–3.91 GHz, and 1550 MHz from 6.28–7.83 GHz, which
are able to cover the 2.5/3.5 GHz WiMAX band and C-band
respectively. A little variation in between the simulated and
measured result may be due to the fabrication tolerance
caused by thickness uncertainty, SMA soldering effect etc.
DIMENSION OF THE ANTENNA
Parameter
W Wp1 Wp2 Wg1 Wg2 Ws1 Ws2 Wsm Wsl
Value (mm)
20
9.5
Parameter
L
Value (mm)
20
9.5
6
6
8
8
1
0.5
Lp1 Lp2
Ls1
Ls2
Lg
Lsm
Lsl
Rcs
3.5
0.5
0.5
4
13.5
4
2.5
16
SIMULATION AND MEASUREMENT
701
the gain of the designed multiband antenna. With the
guidance from IEEE standards [25] and Friis transmission
equation [26], the peak gain is measured by utilizing two
identical horn antennas whose gain and radiation patterns are
known. For the lower operating bands, at 2.53-2.89 GHz the
average gain is 2.43 dBi whereas for the band 3.47-3.91 GHz
the gain is obtained 2.67 dBi. The average gain for upper
band at 6.28-7.83 GHz is achieved 4.57 dBi which in turn
increases directivity of the designed antenna. The radiation
efficiency of the proposed antenna 87.7% is achieved at
upper C-band with average efficiency over the band is
86.31%. On the other hand for the WiMAX bands, the
achieved average antenna efficiencies are 79.9% and 81.8%
at 2.63 GHz and 3.66 GHz center frequency respectively.
Figure 3. Measured and simulated return loss of the proposed antenna
Fig. 4 describes the measured far-field radiation patterns
in E-plane and H-plane for the frequencies at 2.66 GHz, 3.65
GHz, and 6.58 GHz. The presented results indicate fairly
good and steady patterns in the plane over the operating
frequency bands. The co-polarization patterns for E- and Hplane are almost symmetric and directional. Whereas the
cross polarization radiation patters at different operating
frequency bands though seems almost similar, however its
effect observed to be increased with the increased
frequencies as predicted. It has been observed that the
designed antenna performs well in producing nearly
balanced radiation pattern radially for operating bands by
maintaining low cross polarization. These performance
criteria would be certainly beneficial while designing
antenna arrays, thus reasonably would produce more stable
radiation pattern across the operating frequency bands.
Figure 5. Surface current distribution for the inverted-A shaped patch for
a) 2.66 GHz, b) 3.65 GHz and c) 6.58 GHz
A comparison table (Table II) is presented which shows
the itemized performance characteristics in terms of effective
electrical area of patch, bandwidth and maximum gain
between the proposed antenna and some existing multiband
antennas. It has been found through comparison that the
proposed antenna outperforms than the others by providing a
bit wider bandwidth, higher gain and occupying less
radiating patch area.
Figure 4. Measured radiation patterns of the proposed antenna at 2.66
GHz, 3.65 GHz and 6.58 GHz.
TABLE II.
Fig. 5 illustrates the simulated surface current distribution
of the radiating patch element of the proposed inverted-A
shaped antenna at 2.66 GHz, 3.65 GHz and 6.58 GHz
resonant frequency respectively. It has been revealed through
observation that the distribution of current is much stronger
in upper band resonant frequency than the lower bands
resonant frequencies which in turn validate the radiation
efficiency and gain. Free-space ranges are used to measure
702
PERFORMANCE COMPARISON BETWEEN THE PROPOSED
ANTENNA AND SOME EXISTING ANTENNA
Author
Patch area
(mm2)
Bandwidth
(MHz)
Max Gain
(dBi)
[11]
[23]
[24]
Proposed
25x25
23x30
40x50
20x20
300, 500, 700
290, 290, 700
180, 150, 170
360, 440, 1550
2.15, 2.47, 4.13
2.29, 0.9, 3.45
1.7, 2.3, 4.1
3.62, 3.67,5.7
IV.
CONCLUSION
A modified inverted-A shape slotted patch antenna is
presented in this paper through design, simulation and
experimental analysis. Multiband capabilities have achieved
with simple design structure without addition of any spare
elements. The experimental results show reasonably good
operating bandwidths of 360 MHz (2.53–2.89 GHz), 440
MHz (3.47–3.91 GHz) and 1550 MHz (6.28–7.83 GHz) with
3.62 dBi, 3.67 dBi and 5.7 dBi gain. Additionally, it has been
found that the proposed antenna exhibits almost steady
radiation pattern and consistent efficiencies at operating
bands. The optimized dimension of the proposed antenna is
20x20x1.6 mm3 whose measured properties are well suited
for WiMAX and C band satellite applications. The proposed
antenna is significantly reduced in size with better
performance compare to other reported antennas.
[11]
[12]
[13]
[14]
[15]
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