Wireless Personal Communications (2023) 130:165–189

https://doi.org/10.1007/s11277-023-10280-z

The Effect of Miniaturized Circular Antennas on the SAR

Reduction for Wireless Applications

Hamza Ben Hamadi1 · Said Ghnimi1 · Lassaad Latrach1 · Philippe Benech2 ·

Ali Gharsallah1

Accepted: 23 February 2023 / Published online: 13 March 2023

© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2023

Abstract
This work, presents the design and realization of two new miniaturized circular antennas
as well as their effects on the human body. The first step consists in simulation each bi-
band antenna at 2.5 GHz and at 5.2 GHz for wireless applications using the simulators
HFSS and CST Microwave studio. The second step is manifested by the type of perme-
ability substrates, the modifications of the radiating element and the ground plane as well
as the modification of the feeding technique. All these miniaturization methods were used
to limit the peak of specific absorption rate (SAR) in the human body. The SAR is calcu-
lated on a 1 and 10 g tissue mass respectively. The performed tests show that the SAR rate,
which affects the human body tissues and obtained by the antenna with a full ground plane,
is lower than that provided by the antenna with a truncated ground plane. Furthermore, the
SAR rate observed in the different frequency bands for the antenna 2 complies with the
standards proposed by the international commission on non-ionizing radiation protection.

Keywords Antenna miniaturization · Circular patch antenna · CST simulator · Specific

absorption rate

1 Introduction

The circular patch antennas have been extensively studied and used, especially in wire-
less communication systems [1–38], due to their light weight, ease of fabrication, com-
patibility with all electronic devices and low profile. However, they have some draw-
backs. In fact, they have high profiles up to 1/4 λ0 (λ0 is the free space wavelength)
and ranging narrow bandwidth. They are also difficult to integrate. Therefore, multi-
band planar antennas designed for various applications are an alternative solution to the
reconfigurable antenna systems and broad band’s [2–5]. Moreover, several techniques

* Said Ghnimi
said.ghnimi@gmail.com
1
Laboratory of Electronics and Microwave, Faculty of Sciences of Tunis, Tunis El Manar
University, Tunis, Tunisia
2
Laboratory of Electrical Engineering, Grenoble INP, CNRS, University of Grenoble Alpes,
Grenoble, France

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Vol.:(0123456789)
166 H. B. Hamadi et al.

were used to design this multi-band structure. For instance, we can mention applying
parasitic elements [6], using stacked patches with hole-coupled feed networks [7, 8],
electromagnetic coupling feeds [9–11] and utilizing Two-layer annular ring structure
[12–14]. Indeed, the latter technique applied to obtain a dual-band consists in adding
the annular ring to achieve a dual-frequency operation. Another, the authors in [15–17],
proved that the microstrip feeding, is easy to model, increases spurious radiation and
offers a wider bandwidth. In addition, the distance between the feeding line and the
radiating patch can be used to match the antenna impedance. However, the main prob-
lem of these works is how to reduce the mutual interaction between these proposed
antennas and the human body. In [18–20], the authors, design a miniaturized weara-
ble dual-band antenna put on a rigid substrate and operable for wireless local area net-
work applications. The electrical and radiation characteristics of the developed antenna
were obtained by means of the technical insertion of a slot to tune the operating fre-
quencies. Moreover, when the antenna was backed by the artificial magnetic conduc-
tor AMC plane, the gain and the front-to-back ratio of the AMC backed PIFA antenna
was also enhanced [21, 22]. Then, to ensure that the proposed design is harmless to the
human body, this prototype was placed on human tissue cubic model and was observed
that, due to the inclusion of an AMC plane, the peak specific absorption rate (SAR)
decreased. However, the main problem of these works is how to reduce the mutual inter-
action between these proposed antennas and the human body.
All these research work, best answers the question that comes up frequently and which
is technical and biological: what are the levels of effects of EM fields on the health of
the human body?. But so far, we do not find clear answers that answer our problem in a
convincing way. But the answers provided by these studies have significantly reduced the
uncertainties and have enabled a reliable and possible assessment of the possible risks.
In this sense, we have studied in this work the same problem to know how to reduce the
mutual interaction between these proposed antennas and the human body. The main objec-
tive of our study is to design a new multi-band antenna with reliable electricity and radia-
tion characteristics, and with reduced mutual electromagnetic interaction with the human
body. For this, we used the miniaturization methods to reduce the interaction in terms of
the specific absorption rate on a portion of either 1 g or 10 g.
This manuscript is structured as follows. In Sect. 2, the design and the realization
of two miniaturized antennas are presented. Section 3 includes the simulations and
the experimental characterizations of these antennas, by analyzing the influence of the

Fig. 1  Geometry of a circular patch antenna

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 167

Fig. 2  Equivalent circuit of a

circular patch antenna

miniaturization technique on specific absorption rate. Finally, Sect. 4 presents a brief

conclusion and the recommendations for further studies.

2 Antenna Design

The wireless communication system must be equipped by several types of antennas. The
latter have different requirements, namely increased gain and extended frequency band.
They also suffer from various problems, such as fabrication cost, space requirements,
etc. Therefore, our objective is to design miniaturized antenna with simple multi-band
operation, with small size and high gain. To this end, we focused in this work on cir-
cular patch antenna fed in different ways for the UHF and SHF bands with simple and
diverse geometry.

Fig. 3  Photograph of the experimental setup a network analyzer b anechoic chamber

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168 H. B. Hamadi et al.

2.1 Material and Methods

2.1.1 Material

The main geometrical parameters of the designed antenna are the patch radius ‘a’ and
the type of dielectric substrate. The specifications of the antenna design are based on
two different substrates respectively; namely the Rogers RT5880 (ϵr = 2.2) and the FR-4
(ϵr = 4.3). In addition, feeding, which affect the input impedance matching, polarization,
operating modes, radiation interference, surface waves and antenna geometry, should be
taken into account in the design of the microstrip antenna. While both types of feeding
(coaxial probe and microstrip line)have the same equivalent circuit, the latter is formed by
a parallel RLC network representing the radiating metal patch and an inductance showing
the coaxial probe feeding or the microstrip feed line [23, 24].

2.1.2 Method

Once the type and shape of the antenna was determined, we chose two methods to char-
acterize its electrical and radiation performance. The first method is based on modelling
techniques using HFSS and CST Microwave studio, while the second relies on the experi-
mental methods where the electrical and radiation performances of the proposed antennas
(reflection coefficient, radiation pattern) was evaluated using a vector network analyser and
an a far-field anechoic chamber) (Fig. 1).
Before studying these two numerical and experimental methods, we tried to optimize
the antenna proposed by different miniaturization techniques (Fig. 2).

2.2 Characterization of a Miniaturized Antenna

2.2.1 Quality Factor Consideration

After several researches, it has been concluded that the reduction in the size of an antenna
minimizes the bandwidth and gain. Furthermore, it has been widely recognized that there
is a theoretical lower limit to the Q that can be expected for a small antenna. If we consider
that the latter is enclosed in a sphere, the quality factor Q for a lossless antenna is given by
[25]:
1 1
Q= + (1)
Kr Kr3
where k represents the wave number equal to:
K = 2𝜋∕𝜆 (2)
where λ represents the wavelength of the antenna at its operating frequency and r is the
minimum radius of the sphere that completely surrounds the antenna. Therefore, the
decreasing of the size of an antenna results in an increase of the quality factor Q and a
reduction in the bandwidth. It is, thus, possible to minimize the Q of the antenna while
decreasing its efficiency and gain (Fig. 3).

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 169

Fig. 4  Geometry of antenna fed by a microstrip line (Ant.1); a top view, b back view

Fig. 5  Geometry of the radiating

patch (Ant.1 with slot)

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170 H. B. Hamadi et al.

Table 1  Antenna dimensions Parameter Value (mm)

(Ant1)
L 70
W 70
A 25
D 17
h 1.52
Wm 70
Lm 50
R 36

2.3 Antenna Structure

In order to study the characterization of miniaturization, we used two types of antennas to

show the effect of miniaturization on the human body.
The design of the first circular patch antenna fed by a microstrip line to operate at the
resonant frequency of 2.4 GHz is presented in the figure below. In fact, the radiating plate
and the antenna feed were puton the substrate. At the same time, the ground plane was
placed under the substrate. The Rogers RT5880 with a thickness 1.52mm was used as a
dielectric substrate to design our structure. The microstrip line started with an SMA con-
nector pin with a width equal to 0.9 mm and a length of 15.53 mm.
Theoretically, the resonant frequency of the circular patch antenna excited by a micro-
strip line can be determined from its radius (a) using:
F
a= (
(3)
( ) )1∕2
2h nF
1+ 𝜋𝜀r F
[ln 2h
+ 1.7726]

where

8.791 ∗ 109
F= √ (4)
fr ∗ 𝜀r

Therefore, the effective radius of the patch was used and given by:
( )1∕2
2h 𝜋a
( )
ae = a 1 + [ln + 1.7726] (5)
𝜋𝜀r a 2h

While the TM11 mode is widely used in circular patch antenna design, the resonant fre-
quency for the dominant TM11 is indicated by:
1.8412 ∗ C
(f r1 )11 = √ (6)
2𝜋 ∗ ae ∗ 𝜀r

where c is the velocity of light in free space.

We first noticed that the bandwidth provided by the radiating element is higher than
that obtained by the first structure (Fig. 4) although the central frequency of operation was
2.4 GHz and the required polarization was circular. In the second step and to obtain the

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 171

Fig. 6  Geometry of the antenna 2

fed by a coaxial probe (Ant.2); a
top view, b cross-sectional view

multi-band, a circular ring slot was inserted on the patch by adjusting its dimensions to
have a dual-band operation. After adding the slot to the patch, another band was gener-
ated at 5.2 GHz, as shown in Fig. 8. By increasing or decreasing the size of the slot, the
resonance frequency shifted to either a lower or higher band to cover the WLAN band (5.2
GHz).
The antenna 1(Ant1) dimensions are given in Table 1.
Based on Eqs. 3–6, we succeeded in designing an antenna operating in both the 2.5
GHz and 5.2 GHz WLAN frequency bands. However, this structure has some disadvan-
tages such as its huge size (70*70*1.52 ­mm2) and the very high back radiation it produces
(Fig. 5).
To overcome this problem, we applied various miniaturization techniques to propose
another structure, which can operate in the same frequency bands, and to minimize the size
of the antenna and reduce the amount of radiation absorbed by the human body.

2.4 Antenna Miniaturization Techniques

2.4.1 High Permittivity Dielectric Loading

The size of a microstrip antenna can be simply reduced by enhancing the relative permit-
tivity (εr) of the substrate material, as shown in Eq. (6) where the lowering resonance

13
172 H. B. Hamadi et al.

frequency is obtained from the relationship between the speed of light and the dielectric
permittivity.

1 C
C= √ = √ 0 (7)
𝜀∗𝜇 𝜀r ∗ 𝜇r

We notice that, with the increase of the relative permittivity, the speed of light decreases.
In a resonant structure, the slower speed implies that a charged object of dielectric mate-
rial of εr > 1 exhibit sallower resonance frequency than an uncharged structure of the same
size. Therefore, it can be side that these charged structures are "electrically larger", com-
pared to their uncharged counter part of the same physical size. The structure of the circu-
lar antenna, printedontheFR-4 substrate, whose size is (W * L), thickness equals to 1.6 mm
and relative dielectric constant is 4.4, is demonstrated in Fig. 6.

2.4.2 Modifications of the Ground Plane

Microstrip antennas can be further miniaturized by changing the dimensions of their

ground plane. Typical designs of this type of antenna are based on the premise that the
ground plane is infinite, which is not the case in any practical design. To ensure better
miniaturization, the dimensions of the ground plane are reduced again to be larger than
the dimensions of the patch. These antennas with truncated ground planes were studied
experimentally in several works such as [26, 27]. In these studies, it was noted that the
polarization purity of these antennas was poor and that the reduction in ground plane size
also affected the input impedance. Furthermore, the diffraction at the edges resulted in sig-
nificant back lobe radiation, which minimized the front-to-back ratio.
The reduction in the size of the ground plane is not the only modification to the minia-
turization of a microstrip antenna. Other modifications, including the creation of different
types of slots in the ground plane, are also possible, which allows increasing the current
flow in the patch area. Thus, the resonance frequency’s lowered and the size of the antenna
is reduced. Many designs, where slot in the ground plane was used, were proposed in the
literature to miniaturize microstrip antennas [28, 29].
In this work, the dimension of the ground plane is minimized by performing a paramet-
ric study in order to keep the same performance of the basic structure (ant.1) and maintain-
ing the same resonance frequency and the bandwidth. Through this parametric study, a
reduction of 28.6% of the size of the antenna is obtained.

2.4.3 Reshaping or Introducing Slots

The miniaturization of a circular patch antenna can also be achieved by choosing different
types of shapes and slots on the radiating patch, which generates a considerable electrical
length [30] and reduces the antenna size while minimizing the bandwidth. The modifica-
tion may also be done by using different slots in the microstrip patch. If these slots are
properly designed, they will provide a longer electrical length for the current propagation.
In fact, many studies proved that a circular ring slot of 1 mm width reduces the size of the
antenna by 28% and produces a second resonance frequency (5.2 GHz).
The antenna geometry, comprising an annular ring, surrounds a small circular patch on
top with ground plane, as shown in Fig. 6. The radius of the integrated circular patch in

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 173

Fig. 7  Imagesof the fabricated antennas prototypes, a Ant.1; antenna fed by a microstrip, b Ant.2; antenna
fed by a coaxial probe

Table 2  Antenna dimensions Parameter Value (mm)

(Ant2)
L 50
W 50
R1 16
R2 18
D 6
h 1.6

Table 3  Table of Bessel n Kn1 Kn2 Kn3

functions
0 2.405 5.520 8.654
1 3.832 7.016 10.174
2 5.135 8.417 11.620

the annular ring is R1 and the gap between the outer ring and the central circular patch is 1
mm. The resonance frequency of the lower mode was determined by the larger outer ring
radius (Eq. (9)).
Indeed, various studies showed that the use of coaxial cable for feeding patch antennas
is more beneficial because of the simplicity of manufacture with less sensitivity to external
interference. However, there is a need to improve the performance of the antenna param-
eters such as return loss, efficiency and input impedance within the stated frequency range.

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174 H. B. Hamadi et al.

Table 4  Electrical characteristics Simulated Measured

of antenna 1 (Ant.1)
central Band- S11 [dB] central Band- S11 [dB]
frequency width frequency width
[GHz] [GHz] [GHz] [GHz]

2.5 0.39 − 26 2.5 0.2 − 24

5.2 0.51 − 27.5 5.25 0.2 − 12.4

Fig. 8  simulated and measured return loss of the proposed antenna (Ant.1)

In general, coaxial feeding enhances all the antenna parameters, except the gain, relative to
microstrip line feeding [31].
For this reason, the antenna was fed, in the performed experiments, by a coaxial cable
through a hole at the bottom layer with probe radius of 0.035 mm and ground plane size of 50
mm*50 mm, as revealed in Fig. 6b.
The antenna 2 (Ant2) dimensions are given in Table 2.
The purpose of the present analysis is to reduce their operating center frequency by modi-
fying the wave propagation conditions between the radiating patch and the antenna ground
­ M01 mode. With adequate modifications of feeding location, shape
plane and by exciting the T
­ M01 mode was excited. Indeed, the latter offers a higher gain [32, 33],
and patch size, the T
­ M02 ­andTM11.
with a lower operating frequency than the other modes, in particular T
The operating frequency for the TM mode is given by:

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 175

Fig. 9  Simulated and measured radiation pattern in two planes (E-plane; H-plane) at a 2.5 GHz and b
5.2 GHz

Knm ∗ C
(f r2 )nm = √ √ (8)
2𝜋∗ R2 ∗ h ∗ 𝜀r

where ­Knm is the mth root of the Bessel equations, J­ n. Table 3 presents some values of K­ nm.
To operate in the same frequency bands as the base antenna structure (ant.1), the first reso-
nance frequency was set to 2.5 GHz, while the radius of the annular patch R2 was determined
using the following formula [5]:
K01 ∗ C
R2 = √ √ (9)
2𝜋∗ f r2 ∗ h ∗ 𝜀r

The second frequency of the band (f = 5.2 GHz) was produced by a parametric study
through the addition of a slot consisting of an annular ring of width equal to 1mm.
In order to design the two created antennas, simulations and measurements were carried
out to study the various radiation characteristics and to minimize the specific absorption rate.

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176 H. B. Hamadi et al.

Fig. 10  Simulated and measured return loss of the designed antenna (Ant.2)

Table 5  Electrical characteristics Simulated Measured

of antenna 2 (Ant.2)
central Band- S11 [dB] central Band- S11 [dB]
frequency width frequency width
[GHz] [GHz] [GHz] [GHz]

2.54 0.12 − 26 2.5 0.1 − 17

5.2 0.22 − 28 5.06 0.25 − 14.7

Table 6  Comparison of the Standard Wifi/bluetooth WLAN Wifi/bluetooth WLAN

designed antennas
Return − 24 − 12.4 − 17 − 14.7
Loss at
[− 10 dB]
Gain [dBi] 4.6 4.2 3.3 3.02

3 Results and Discussion

To validate the performance of the designed antennas, the latter, having given dimensions,
were fabricated and their electrical and radiation characteristics were measured. It should be
specified that the fabricated patch and the ground plane were made of a copper sheet with
0.035 mm thinness (Fig. 7).
The chosen substrates are:

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 177

Fig. 11  Simulated and measured radiation pattern in the two planes (E-plane; H-plane) at a 2.5 GHz and b
5.2 GHz

• Ant.1: Rogers 5880 of relative permittivity εr=2.2 and thickness: h= 1. 52 mm.

• Ant.2: The epoxy -FR4 of relative permittivity εr =4.4 and thickness h=1.6 mm.

Simulation results, such as RL (=S11) return loss and radiation patterns of two resonant
frequencies, were verified by a vector network analyzer and anechoic chamber to determine
the actual performance of the designed antennas.

3.1 Electrical and Radiation Characteristics of the Proposed Antenna

In Figs. 8 and 9, the simulation and measurement results of the reflection coefficient and
the radiation pattern are verified at the antenna excited by a microstrip line (Ant.1).
The measurement results of the radiation pattern in the co-polarized and cross-polar-
ized E and H planes at the two frequencies 2.5 and 5.2 GHz are obtained with a stargate
anechoic chamber as shown in Fig. 9. The agreement is poorer for the cross-polarization
components for both frequency bands, which may be due to the coupling between the
antenna and the feeder cables. A diagram identical to that of a monopoly antenna is

13
178 H. B. Hamadi et al.

Fig. 12  Human tissue models

obtained in the upper band, whereas in the lower band, it has unidirectional radiation.
According to these results of the measurements of the diagram in the two planes E and
H, the antenna has a more important back radiation.
The simulated and measured results of the return loss |S11| and radiation pattern of the
proposed antenna (excited by a coaxial cable, Ant.2) are almost identical, as shown the
Fig. 10 (Table 4).
The measured impedance bandwidths with 10 dB return loss, centered at 2.4 GHz and
5.2, respectively, are 27% and 36.5%. The simulated results are better than the measured
findings because of the losses in cables. In Table 5, the simulated and measured electrical
characteristics of the proposed antenna are compared.
The measured radiation patterns in both xoy and yoz planes at 2.5 GHz and 5.2 GHz,
shown in Fig. 11, agree well with the CST.
If we refer to the results of the measurements of the radiation pattern, the miniature
antenna has a higher radiation for the positive Z, while its rear radiation is lower com-
pared to the basic structure (Fig. 9), In Indeed, the reason is that the main radiating struc-
ture is the upper patch of the antenna, the ground plane protects the patch, thus reducing
the coupling between the upper patch and the human body. On the other hand, the lower
band (2.5 GHz) is more sensitive to the presence of the human body, since the mass of our
structure also contributes to the radiation, which will directly cause a coupling with the
human tissue. However, attenuation is observed in both simulated and measured patterns,

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 179

Fig. 13  Dielectric properties of

the biological tissues. a Relative
permittivity. b Conductivity

this attenuation is always greater than 10 dB in most situations. These demonstrated prop-
erties of the antenna make it an ideal candidate for potential wearable devices for medical
applications.
From these results, the electrical characteristics of the designed antennas are com-
pared in the Table 6. It was found that the second antenna, with a smaller patch area,
has a narrower bandwidth and a lower gain, compared to the first antenna. This result
is explained by the effect of miniaturization on the radiation characteristics of the
microstrip antenna.

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180 H. B. Hamadi et al.

Fig. 14  Antenna over the human

model

3.2 Effect of Miniaturization on SAR Reduction

The use of the wearable antennas and its impact on the human body laid several problems.
To overcome these issues, current regulations around the world allow manufacturers to
keep the SAR limits of tissue at 2 W/kg and 1.6 W/kg for 10 g and 1g, respectively. For this
reason, both types of antennas were placed, in the performed experiments, on the human
model voxel to study SAR. Figures 12 and 13 present the dielectric properties of the four-
layer voxel model in the frequency range from 2 to 7 GHz.
The four-layer voxel model was developed by the CST Studio commercial software
package. The antenna was put at a 5 mm distance far from the human body because this
distance represents the standard clothing thickness (Fig. 14).
Based on the obtained reflection coefficients, it can be seen that the microstrip line
antenna (Ant.1) did not perform well in both frequency bands (Fig. 15) due to a frequency
shift. The latter was caused by the high dielectric charge of the body, which affected the
polarization of an antenna structure with a truncated ground plane. On the contrary, the
study of the reflection phase of the miniaturized antenna (Ant.2), allowed obtaining both
operating bands, but with a decrease of the matching level.

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 181

Fig. 15  Simulation results of the designed antenna (Ant.1)

The following figures show the SAR rates in (2.45, 5.2) GHz of the two antenna struc-
tures (Ant.1 and Ant.2) at (1g) and (10g) according to the ICNIRP standard.
The SAR levels, which affected the human body tissues andobtained from the latter
structure (Ant.2), are lower than those provided bythe basic structure (Ant.1). Measured
at 1 and 10 g in both operating bands, they were lower than 1.6 and 2 W/kg, respectively.
This result was obtained through significant modifications of the antenna parameters. In
addition, the SAR rate was successfully limited to comply with the international guidelines
(ICNIRP).
To conclude, the electromagnetic interaction is manifested respectively by the electri-
cal characteristics (resonance frequency and the width of the bandwidth) and the radia-
tion characteristics (polarization and radiation pattern). Based on the results obtained in
Fig. 15, he presence of the human body modifies these characteristics (Ant. 1), knowing
that, when using the different miniaturization techniques, the presence of the human body
does not affect these characteristics of the antenna 2 (Ant. 2) shown in Fig. 16. Same thing
in these Figs. 17, 18, 19 and 20, we observe that the specific absorption rate of the antenna
2 (Ant. 2) is very reduced compared to the basic antenna (Ant. 1).

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182 H. B. Hamadi et al.

Fig. 16  Simulation results of the developed antenna (Ant.2)

Fig. 17  SAR distribution of the “Ant.1” at 2.45 GHz for a 1 g, b 10 g

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 183

Fig. 18  SAR distribution of the “Ant.1” at 5.2 GHz for a 1 g, b 10 g

Fig. 19  SAR distribution of the “Ant.2” at 2.45 GHz for a 1 g, b 10 g

Finally, the designed antenna was comprehensively compared with other antennas
designed in previous research works. The comparative study is shown in Table 7. Com-
pared to the existing antennas, the proposed SAR reduction technique is efficient in terms

13
184 H. B. Hamadi et al.

Fig. 20  SAR distribution of the “Ant.2” at 5.2 GHz for a 1 g, b 10 g

of compactness as no additional unit is required. The final design also produced a remark-
able enhancement in the radiation efficiency.
Based on the results obtained in the above table, we can note that the miniaturi-
zation has led to a reduction in some electrical and radiation characteristics such as
bandwidth and antenna gain, but also to an improvement in the absorption of electro-
magnetic waves where the SAR is reduced by almost 84% in the lower band and by
95% in the upper band.

4 Conclusion

In this paper, we presented an overview of the different methods used to miniaturize circu-
lar antennas. Indeed, the high permeability substrate, the modification of the radiating ele-
ment and the ground plane as well as the modification of the feeding technique were used
to limit the peak of SAR in the human body and the size of the antenna.
The obtained results showed that the design of miniaturized circular antennas has a pos-
itive effect on the reduction of body coupling and back radiation. Compared to the conven-
tional patch antenna, the SAR value decreased from 6.8 to 0.92 W/kg, in the lower band,
and from 7.67 to 0.34 W/kg in the upper band, which allowed a wider use of body-worn
antennas. To fully characterize this type of antenna, real tests of the antenna on the human
body will be performed in our future study.

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 Table 7  Comparative studies
References Reduction technique Operation Bandwidth SAR reduction
(W/kg)

[34] Larger ground plane and Monoband 35% 35%

High εr Substrate
[35] polymeric ferrite sheets Monoband – 85.5%
[36] SRR Dual-band 5% and 3.6% 93%
[37] EBG Monoband 14.7% 97.1%
The Effect of Miniaturized Circular Antennas on the SAR Reduction…

[38] FSS Monoband 22.4% 83.6%

This work Larger ground plane, High Dual-band 3.9% and 4.8% 84.5% and 94.9%
εr Substrate and shapes
of the radiating patch
185

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186 H. B. Hamadi et al.

Author contributions The ethics approval, the consent to participate and the consent for publication
between authors (Yes, compatibility is present.

Funding The research was not funded or supported by any party.

Data availability I confirm the transparencies of data and material.

Code availability Not applicable.

Declarations
Conflict of interest The authors declare that they have no conflict of interest.

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188 H. B. Hamadi et al.

Hamza Ben Hamadi received a degree in electronics bachelor in 2014

and M.Sc. degree in electronics from El-Manar University—Sciences’
Faculty of Tunis, Tunisia, in 2017. His research interests include
microwave-integrated circuits, antenna and propagation.

Said Ghnimi received a degree in electronics engineering in 2004,

M.Sc. degree in electronics device from El-Manar University—Sci-
ences’ Faculty of Tunis, Tunisia, in 2006 and Ph.D. degree in electron-
ics engineering at the Sciences’ Faculty of Tunis, in 2010. His
research interests include Electro-Magnetic Compatibility (EMC), tel-
ecommunication systems, Microwave Engineering.

Lassaad Latrach received a degree in electronics engineering in 2004,

M.Sc. degree in electronics device from El-Manar University—Sci-
ences’ Faculty of Tunis, Tunisia, in 2006 and Ph.D. degree in electron-
ics engineering at the Sciences’ Faculty of Tunis, in 2009. His
research interests include multilayered structures and microwave-inte-
grated circuits.

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The Effect of Miniaturized Circular Antennas on the SAR Reduction… 189

Philippe Benech received the M.S. degree in microelectronics from

the University of Montpellier, in 1987, and the Ph.D. degree in instru-
mentation from University Grenoble, France, in 1990. Since 2000, he
has been a Professor with the University of Grenoble Alpes. His
research interests include the domain of radio frequency components,
devices, and integrated functions.

Ali Gharsallah received the degree in radio-electrical engineering

from the Engineering School of Telecommunication of Tunisia in 1986
and the Ph.D. degree in 1994 from the National School of Engineering
of Tunisia. Since 1991, he has been with the Department of Physics at
the Sciences’ Faculty of Tunis. His current research interests include
antennas, array signal processing, multilayered structures, and micro-
wave-integrated circuits.

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