1
Journal of Integrated Circuits and Systems, vol. 14, n. 2, 2019
Bio-Inspired On-Chip Antenna Array for ISM Band 60 GHz Application
P. F. da Silva Júnior1, E. E. C. Santana1, M. S. S. Pinto1, A. J. R. Serres2, C. C. R. de Albuquerque2, R.
C. S. Freire2
1
Post-graduation Program in Computer Engineering and Systems (PECS) State University of Maranhão,São Luís, Brazil
2
Post-graduation Program in Electrical Engineering Federal University of Campina Grande. Campina Grande, Brazil
e-mail: pfs1224@gmail.com
Abstract—A flower-shape bio-inspired aperture-coupled antenna array for on-chip application, generated by Gielis formula, operating in industrial, scientific and medical (ISM)
band at 60 GHz (57 GHZ to 64 GHz) is presented in this paper. The antenna proposed is composed of a transmission feed
line followed by an aperture and patch element simulated in
aluminum, with 2 micrometers of thickness, lying on two layers of silicon with 200 micrometers of thickness each. Dimensions of the antennas were calculated according to the effective
wavelength for the resonance frequency at 60 GHz. Simulations were performed in the commercial software ANSYS®
Electronics Desktop. The use of the bio-inspired flower-shape
promotes more compact structures with greater perimeter,
rearranging these shapes into an antenna array provided a
gain and a bandwidth increase in the design, 3.11dBi and
2.86GHz, respectively, which resulted in a maximum gain of
8.82 dBi and a total bandwidth of 5.88 GHz.
Index Terms— On-chip, aperture-coupled antenna array,
bio-inspired flower-shape, industrial scientific and medical
band.
I. INTRODUCTION
The increasing use of the electromagnetic spectrum for
various technologies has promoted researches in higher frequency bands, especially in the millimeter wave range (30 –
300 GHz). The industrial, scientific and medical (ISM)
band in the 60 GHz range (57 – 64 GHz), normalized by the
Federal Communication Commission (FCC), has a bandwidth of 7 GHz and it is usually used for high data rate
wireless communication [1]. The frequency range of ISM
60 GHz includes other technologies such as Wireless Fidelity (Wi-Fi) and wireless personal local area network
(WPAN), relevant topic when related to the reduction of
components and systems for the internet of things [2-3].
The development of broadband antennas in silicon at
60 GHz range has the advantage of being used inside integrated circuits considering the mutual interference, the electromagnetic coupling and the standards stablished for each
technology, so, the use of aperture-coupled antennas is well
suited for this application since it promotes high gains with
compact structures [1-5]. Aperture-coupled antennas are
broadband antennas used in many applications and technologies, such as the ones defined in [6-9], since they have
compact structures and they are composed of two or three
layers. Generally, the layers are the transmission feed line,
the aperture and the patch elements, and, in some cases, one
parasite patch element, separated by dielectrics with different permittivity. The well-known modeling of patch antennas, coupled with the use of a low-cost dielectric and a radiating element, such as silicon and aluminum, respective-
Digital Object Identifier 10.29292/jics.v14i2.53
ly, enables a versatile antenna design. In [10], it was observed the comparison between aperture-coupled patch antennas operating in the industrial, scientific and medical
band at 60 GHz (57 – 64 GHz). It was studied square and
circular shapes, the first one presented a more compact
structure with dimensions smaller than 1.55 mm.
According to [6, 11-12] the resonant frequencies of a
patch antenna are determined by its length and the perimeter of the radiating element. Thus, elements with larger perimeters operate at lower frequencies, with the use of circular forms or near-circular shapes, only the perimeter should
be considered. The use of the bio-inspired forms allows the
development of compact structures with larger electrical
perimeters, operating at lower frequencies [12]. Plant
shapes were used in the development of some antennas,
built in fiberglass, denim and transparent materials, such as
cellulose acetate with Indio tin oxide film, operating in
UWB applications [13], LTE bands at 700 MHz [12], 2G,
3G and 4G [14], and WLAN [15-16].
Arrays are used in the development of antennas to alter
their parameters such as direction of lobules, bandwidth,
gain, multiple resonances and others, considering numbers
and dimensions of radiating elements [6, 17]. A wideband
log-periodic array with five dissimilar square size patch elements was described in [18], dual-band arrays were proposed with the use of dissimilar rectangular size patch elements in [19], and also, Dome-shape patches were used in
dual-band array design in [20-21]. The aperture-coupled
antennas for 60 GHz bands presented a variable gain, depending on the type of coupling structure used. In [22] it
was developed balanced-fed and fork-fed aperture-coupled
patch antennas with one, eight and sixteen elements arrays
suitable for broadband millimeter-wave communications at
60GHz, with a gain of 8 dBi for a single element and 17
dBi for a 16-elements array. In [23] it was proposed a 4x4
aperture-coupled patch antenna array with peak gain reaching 21.4 dBi at 60 GHz band. A low-cost aperture-coupled
patch antenna, using the standard printed circuit board
(PCB) process, was proposed for the 60-GHz-phased array
antenna in [24], with measured peak gain of 6.9 dBi at 62
GHz for the single antenna, and measured peak gain from 4
to 7.5 dBi across all four IEEE 802.15.3c channels, for each
antenna element, within the frequency range from 57.2 up
to 64.5 GHz.
This paper presents the development of on-chip aperture-coupled antenna array, bio-inspired in a flower-shape,
generated by Gielis formula, operating in ISM application
at 60 GHz band, simulated in silicon and aluminum. Section II shows the antennas proposed and the materials and
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SILVA JR et al.: Bio-Inspired On-Chip Antenna Array for ISM Band 60 GHz Application
methods used. Section III presents the different results
achieved and, finally, conclusions are drawn in section IV.
II. MATERIALS AND METHODS
Methodological procedures were carried in the development of the flower-shape bio-inspired aperture-coupled antenna array, which were divided into three steps:
1 - Project of the Euclidean geometry aperture-coupled
antenna, with indication of perimeter and feed matching
impedance of quarter-wave transformer for 60 GHz. The
perimeter of this structure is used in the bio-inspired antenna development. With these dimensions, it is designed and
simulated an antenna with circular shape, only to be used as
a base value for the flower-shape antenna perimeter, since
the expected one is a more compact structure with perimeter value close to the one observed in the circular design;
2 - Choice of the bio-inspired shape, which will provide
a higher perimeter and a more compact structure. Then, the
generation of the shape chosen is done by using the Gielis
formula with the use of computer aided (CAD) techniques,
which results in a DXF (Drawing Exchange Format) format
file exportable to the full-wave simulation software, where
it can be optimized, and adjustments can be done in order to
obtain the desired resonance frequency; and
3 – Simulations of the structures, which were performed
in ANSYS® Electronics Desktop, software widely used in
solving electromagnetic problems, which implements fullwave solutions, such as the Moments Method (MoM), Finite Element Methods (FEM), 2D and 3D solutions.
1) Design of on-chip bio-inspired flower-shape aperturecoupled antenna array
A flower-shape was designed using the circular geometry perimeter of an aperture-coupled antenna according to
the effective wavelength, λeff, at 60.5 GHz resonance frequency, applied in patch elements and ground plane. The
λeff can be obtained by:
c
eff
,
(1)
r 1
f0
2
where c is the light speed in vacuum, f0 is the resonance
frequency in Hz and εr is the relative permittivity of the material.
Flower-shapes were drawn using Gielis formula, a polar
transformation that represents circle, square, rectangle, and
ellipse geometries [25]. According to [25], the members of
superellipses group are limited to symmetric structures, defined by:
n
x
y
b
a
n
1.
(2)
Gielis formula uses polar coordinates: r = f(θ), replacing
x = rcos(θ) and y = rsin(θ) and inserting the argument (m/4)
θ, it generates a specific rotational symmetry allowing the
development of similar shapes to those observed in the na-
ture. Gielis formula is defined by:
r f ( )
1
n2
1
1
m
m
n1
a cos 4 b sen 4
n3
,
(3)
were ‘ni’, ‘m’, ‘a’ and ‘b’ are real numbers different from
zero.
The patch element and the ground plane of the antenna
array were generated by Gielis formula and the parameters
are displayed in Table I. The transmission line was calculated according to [26].
Table I. Parameters of the Gielis formula.
m
n1
n2
n3
a
b
-60
30
30
1
1
Shape
Patch = 8
Aperture = 4
The aperture-coupled antenna was designed using silicon
as dielectric material –with a thickness of 200 μm, with dielectric permittivity of εr = 11.9 and loss tangent of 0.001
(the dielectric characterization values were obtained in the
ANSYS® Electronics Desktop data)– and the radiating elements of aluminum with thickness of 2 μm and effective
wavelength of λeff = 1.97 mm in 60 GHz, to match to
50 Ohms. In the development of this project, only the antenna structure was considered, since the antenna can suffer
interferences in the input impedance of the antenna which
could cause resonance frequency, bandwidth, gain, and
HPBW variations, and this is another process that can be
addressed in a separate work. This project considered that
the materials used in other layers, as well as the impedance
at the entrance of the antenna, would not suffer from parasites interference.
The square cut on the aperture layer has 0.5 mm of width
and 1 mm of length. An important topic in the aperturecoupled antennas is the impedance matching of the transmission line and the aperture, which can be changed according to the proximity between them. Since it has a compact structure, small variations can promote the mismatch
of the impedances with the reduction of the return loss, variation of the resonance frequency and the bandwidth.
Fig. 1 shows the development of the on-chip circular and
flower-shape bio-inspired aperture-coupled antenna array,
with dimensions of λeff. Note that the overall antenna size
was reduced when comparing the bio-inspired shape and
the circular shape antennas with one element; hence, the
array structure was developed only for the bio-inspired antenna since this work proposes the reduction of the design
dimensions.
The proximity between those structures causes a small
variation in the resonance frequencies in both antennas,
leading the antennas to resonate at near frequencies to the
ones expected. Comparing with a single structure, it has
two important improvements: the increasing of the gain and
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Journal of Integrated Circuits and Systems, vol. 14, n. 2, 2019
covers part of ISM 60GHz band (57 – 64 GHz). The flower-shape bio-inspired aperture-coupled antenna array presented a shift in the first resonance frequency, compared
with the single flower-shape, of 0.42%. Proximity between
the structures boards generates the second resonance frequency, 61.96 GHz, and increases the bandwidth in
33.84%, which is the expected behavior for the coupling of
the radiating elements in the antenna array [5], covering
84% of ISM 60 GHz band.
the bandwidth. The structures of the circular shape and the
bio-inspired flower-shape, both patch and ground plane
with the layers indication and dimensions, can be observed
in Fig. 1(a) and (b), respectively. The circular shape and
flower-shape antennas are shown in Fig. 1(c). Fig. 1(d)
shows the aperture-coupled antennas and the array proposed. Comparison between the antenna dimensions and a
10mm side chip is shown in Fig. 1(e).
The distance between patch elements in the antenna array
was one λeff size from the center of each structure. Using the
bio-inspired flower-shape provided a 6.67% reduction in
ratio when compared to the circular shape.
Fig.2 Comparison between simulated S11 parameters of on-chip aperturecoupled antennas.
Fig. 3 and Table II shows the curves of simulated gain
(dBi), at resonance frequency, of on-chip aperture-coupled
antennas. According to [13], there is a relationship between
the amount of metal in the radiating element and the gain in
the planar antennas. At resonance frequencies, the bioinspired flower-shape antenna presents gain very close to
the one observed in the circular-shape, with a difference of
1.04 dBi, however, with the insertion of one more element
of same dimension, there is an increase in the power gain
(3.11 dBi), which shows an expected behavior for an antenna array [5], which results in a maximum gain of 8.83 dBi.
The gain observed in the aperture-coupled antenna is compatible with that shown in other works for the 60 GHz frequency range, where gains of 3 to 14 dBi can be verified
depending on the type of coupling structure used [22-24].
Table II. Frequency responses of on-chip aperture couple antennas.
Fig.1 Design of on-chip aperture-coupled antennas: a) structure of the
circular shape; b) structure of the bio-inspired flower-shape; c) circular and
bio-inspired patch and aperture flower-shape with dimensions; d) circular,
bio-inspired flower shape, and antenna array; e) visual antennas in chip.
On-chip aperturecoupled antennas
1
III. RESULTS AND ANALYSIS
2
Circular
shape
Bioinspired
flowershape
Flowershape
bioinspired
array
f0
(GHz)
f1
(GHz)
f2
(GHz)
Bandwidth
(GHz)
S11
(dB)
Gain
(dBi)
58.9
57.51
61.40
3.89
-23.78
4.68
59.11
57.81
60.83
3.02
-45.55
5.72
Fig. 2 shows the comparison between the simulated S11
parameter of aperture-coupled antennas with circular
shape, bio-inspired flower-shape and the bio-inspired an-30.40
59.40 /
57.55
63.43
5.88
/
8.83
tenna array from 50 GHz to 90 GHz band. Table II pre- 3
61.98
-31.29
sents values of first resonance frequency, f1, second resonance frequency, f2, central resonance frequency, f0,
bandwidth, BW, reflection coefficient and gain.
Thus, in the results it is possible to observe the increase
It can be observed that the on-chip circular and the bioof the gain due the use of aperture-coupled antennas of the
inspired flower-shape antennas obtained variation in resosame size, and the increase of the bandwidth due the proxnance frequency of 1.4% and bandwidth of 22.36%, which
imity between the radiating elements.
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SILVA JR et al.: Bio-Inspired On-Chip Antenna Array for ISM Band 60 GHz Application
IV. FINAL CONSIDERATIONS
9.0
8.0
Gain, dBi
7.0
6.0
5.0
C ircular shape
4.0
3.0
B io-inspired shape
Bio-inspired array
57
58
59
60
61
62
63
64
Frequenc y, GHz
Fig.3 Comparison of simulated gain of on-chip aperture-coupled antennas.
The aperture-coupled antennas radiation patterns, with
HPBW indications in resonance frequencies, are shown in
Fig. 4. The antennas presented omnidirectional radiation
patterns, with greater variations for electric (Φ = 0º) and
magnetic fields (Φ = 90º). It can be observed in the bioinspired flower-shape antenna array a more concentrated
half power beamwidth (HPBW) when compared to the bioinspired flower-shape antenna with one element, which indicates a higher signal transmission efficiency in this beam
and represents a positive point to the proposed design. The
difference observed is of 46.97%, shown in Fig. 4(a) and
4(c). Another effect of the use of an antenna array is the increase in current density (53.14%) compared to the bioinspired flower-shape antenna with one element, Fig. 4(b)
and 4(c), with maximum value of 159.36 A/m2.
Gain, dBi
Gain, dBi
Gain, dBi
Fig.4 3D and 2D radiation patterns of on-chip aperture-coupled antennas:
a) circular shape; b) bio-inspired flower-shape; c) bio-inspired array.
In this paper it was simulated an on-chip bio-inspired
flower-shape aperture-coupled antennas, generated by
Gielis formula, operating in industrial, scientific and medical (ISM) band at 60 GHz (57 GHZ to 64 GHz). The proposed aperture-coupled antennas were designed with patch
element simulated in aluminum with 2 micrometers of
thickness, on two layers of silicon with 200 micrometers
each, and simulated in commercial software ANSYS®
Electronics Desktop. All dimensions were calculated according to the effective wavelength for the resonance frequency at 60 GHz to match to 50 Ohms. Using the bioinspired flower-shape provided a more compact structure
with greater perimeter. The bio-inspired flower-shape antenna array caused an increase in the gain of 3.11dBi, compared to other structures, which led to a maximum gain of
8.82dBi, and in the bandwidth of 2.86 GHz, total bandwidth
of 5.88 GHz, covering 84% of ISM band.
ACKNOWLEDGEMENTS
We
greatly
appreciate
the
COPELE/UFCG,
CAPES/COPEX and PECS/UEMA for the support and
funding, without which this work would not be possible.
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Paulo Fernandes