Int’l J. of Communications, Network and System Sciences, 2011, 4, 377-383
doi:10.4236/ijcns.2011.46044 Published Online June 2011 (http://www.SciRP.org/journal/ijcns)
Modified Dual Segment Rectangular Dielectric Resonator
Antenna Terminated in a Bio-Medium
Ravi Kumar Gangwar1, Surya Pal Singh1, Devendra Kumar2
1Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi, In di a
2Department of Ceramic Engineering, Institute of Technology, Banaras Hindu University, Varanasi, India
Received January 27, 2011; revised February 23, 2011; accepted March 15, 2011
Abstract
In this paper, the simulation studies of the radiation characteristics of modified dual segment rectangular di-
electric resonator antenna (DSRDRA) in free space and in presence of bio-medium alongwith the absorbed
power distribution in a homogenous bio-medium (muscle layer) in direct contact with the proposed antenna
are reported at different WiMAX band frequencies. The specific absorption rate (SAR) distributions in mus-
cle layer for different antenna-to-muscle layer spacings are also presented at resonant frequency of antenna
in WiMAX bands. The results of return loss, input VSWR and radiation characteristics of proposed antenna
in presence of bio-medium are also compared with the results for free space. The simulation study has been
carried out using CST Microwave Studio software.
Keywords: Modified DSRDRA, SAR, WiMAX Band, Radiation Pattern
1. Introduction
The proliferation of wireless portable devices and greatly
increased amount of electromagnetic radiation in the
environment from these devices are making the public
aware of the possible health risks of wireless portable
devices. Although the most common fear in people’s
minds is the risk of contracting serious diseases includ-
ing brain cancer due to electromagnetic radiation from
these devices in the long term. So investigations on
wireless portable devices in the vicinity of a human body
are important from the technical point of view [1]. The
human body, being lossy, absorbs certain amount of
electromagnetic radiation generated from wireless port-
able device situated in its vicinity. Therefore, it is of in-
terest to evaluate the power absorbed/specific absorption
rate (SAR) distribution in the body tissues due to wire-
less device antenna radiating electromagnetic waves [2].
The electric field induced and hence SAR within the
human body depends on several factors including the
amplitude, frequency and polarization of the electro-
magnetic wave, and the shape, size and electrical char-
acteristics of the body tissues. As strong interrelation
exists among different parameters of dielectric antenna
including its size, configuration, dielectric constant,
bandwidth, near field distribution and far field pattern;
these parameters will affect specific absorption rate
(SAR) distribution in a bio-medium located close to the
antenna.
The antenna requirements for wireless portable devices
are that the antenna be small, have an omni-directional
radiation pattern, and have a wide bandwidth capable of
operating in that band. Dielectric Resonator Antennas
(DRAs) are considered as one of the most suitable port-
able device antennas due to their low profile, high radia-
tion efficiency, large bandwidth, flexible feed arrange-
ment, wide range of material dielectric constants, ease of
excitation, easily controlled characteristics and ease of
integration with other active or passive microwave inte-
grated circuit (MIC) components [3-7]. The techniques
used to improve the bandwidth of the DRAs include
changing the aspect ratio of DRA, employing multiseg-
ments and stacked DRAs and by varying the dielectric
constant of DRA material. For wider-band applications,
DRAs having lower dielectric constant values are pre-
ferred. This results in week coupling. Multi-segment
DRAs can be used to overcome this problem [8-9].
Only a few studies are reported in the literature on
SAR distribution in bio-tissues due to Dielectric Reso-
nator Antennas (DRAs). The FDTD method has been
applied for computing SAR distribution inside the human
head and the effects of the human proximities including,

378 R. K. GANGWAR ET AL.
the head, the hand, and the user’s glasses on the antenna
performance have been analyzed [10]. Off-centre ring
DRA has been designed and also used for evaluation of
SAR distribution in human head [11]. The performance
of rectangular DRA (RDRA) in close proximity with the
user’s body was studied with the help of a user's hand
model [12].
In this paper, simulation studies of the SAR distribu-
tions in a homogeneous bio-medium (muscle layer)
close to modified DSRDRA, which is fed by a 50 Ω
coaxial probe for WiMAX band (3.2 GHz and 5.0 GHz),
are presented. The radiation characteristics of the pro-
posed antenna and also the SAR distributions in a ho-
mogeneous bio-medium (muscle layer) for different
antenna-to-bio-medium separations of 0 cm, 5 cm, 10
cm and 20 cm at resonant frequency of antenna are
studied through simulation using CST Microwave Stu-
dio software. The simulation results for SAR distribu-
tion in the muscle layer are obtained for antenna input
power of 0.2 W and the effect of reducing input power
from 0.2 to 0.02 W on the maximum SAR (10 g) value
is also analyzed. The results of return loss and radiation
patterns of proposed antenna in free space are also
compared with results of antenna in direct contact with
the bio-medium.
2. Antenna Geometry
The proposed dual segment RDRA consists of lower
segment made from thin teflon sheet with dielectric
constant 12.1
r


r
and an upper segment of alumina
block with 29.8

 as shown in Figure 1. The dual
segment DRA is placed on a ground plane of size 40 ×
15 × 4 mm3. The lower and upper segments of the DRA
have dimensions of a × b × l and a × b × l1 respectively.
The DRA is excited by a 50 Ω coaxial probe of outer
radius 2 mm and inner radius 0.6 mm. The probe height
above the surface of ground plane is found to be 11.6
mm through simulation using CST Microwave Studio
to provide lowest return loss at resonant frequency. A
metallic plate of negligible thickness fully covers the
side of DRA just opposite the side where feed is located.
The design parameters of the antenna are a = 20 mm, b
Figure 1. Geometry of modified DSRDRA.
= 12 mm, l1 = 3 mm, l = 10 mm and probe height = 11.6
mm [13].
3. Results and Discussion
3.1. Return Loss and Input VSWR Characteristics
The return loss and input impedance versus frequency
characteristics for the proposed antenna in free space and
in direct contact with bio-medium has been carried out
using CST Microwave Studio software. The return loss
and input VSWR versus frequency curves of the pro-
posed antenna in free space and in direct contact with
bio-medium have been presented in Figures 2 and 3.
From Figure 2 the resonant frequency, operating fre-
quency range and the percentage bandwidth of the pro-
posed RDRA are extracted. The resonant frequency, op-
erating frequency range and the percentage bandwidth of
the antenna in free space are found to be 5.156 GHz,
3.04 - 5.65 GHz and 50.62% respectively.
From Figure 2 it can be seen that the simulated reso-
nant frequency in the presence of phantom muscle is
4.87 GHz, which is 286 MHz lower than the resonant
frequency of antenna in free space. The frequency
de-tuning in the presence of muscle layer may be due to
the perturbations in both the resonant mode and near
field distribution of the antenna. From Figures 2 and 3 it
Figure 2. Return loss versus frequency curve of modified
DSRDRA.
Figure 3. VSWR versus frequency curve of modified DSR-
DRA.

R. K. GANGWAR ET AL.
379
can be observed that the values of return loss and input
VSWR of the proposed antenna in presence of the syn-
thetic muscle are higher than the corresponding parame-
ter values of antenna in free space. This may be attrib-
uted to wave reflections due to abrupt changes in the
media when antenna is in the vicinity of the bio-medium.
space and in direct contact with phantom muscle layer
are studied at 5.156 GHz through simulation using CST
Microwave Studio software. The simulated radiation
patterns of the proposed antenna in free space and in
direct contact with phantom muscle layer at 5.156 GHz
are shown in Figures 4 and 5 respectively. The far field
parameters are extracted from Figures 4 and 5 and the
results are shown in Table 1.
3.2. Far Field Performance
From Figure 4 and Table 1 it can be observed that the
radiation pattern of the antenna in x-y plane is omni- The far field pattern of the proposed antenna in free
(a) (b)
(c) (d)
Figure 4. Far field performance of modified DSRDRA in free space (a) In x-z plane; (b) in y-z plane; (c) in x-y plane; (d) 3D
pattern.

380 R. K. GANGWAR ET AL.
(a) (b)
(c) (d)
Figure 5. Far field performance of modified DSRDRA in direct contact with Bio-medium (a) in x-z plane; (b) in y-z plane; (c)
in x-y plane; (d) 3D pattern.

R. K. GANGWAR ET AL.
381
Table 1. Far field parameters of dual segment RDRA. butions in a homogenous bio-medium (muscle layer of
size 120 × 120 × 150 mm3), which is separated from the
proposed antenna by 0 mm, 50 mm, 100 mm and 200
mm was carried out assuming input power of 0.2 Watt.
The simulated SAR (10 g) distributions in the muscle
layer in direct contact with the proposed antenna along x,
y and z directions at the antenna resonant frequency of
5.165 GHz and at other frequency 3.31 GHz are shown
in Figure 7. The SAR (10 g) distributions in the bio-
medium for the antenna-to-bio-medium separations of 50
mm, 100 mm and 200 mm at the resonant frequency are
shown in Figure 8. The mass density of muscle layer
available in literature is 1050 Kg/m3 [14]. The complex
permittivity, electrical conductivity of muscle layer
Far field parameters In Free
space In Bio-medium
Directivity in dBi 7.710 7.264
Gain in dB 7.696 2.399
Total efficiency in % 99.69 27.86
x-z Plane 49.4 36.6
3-dB
Beam-width in
deg. y-z Plane 43.4 23.1
x-z Plane No side
lobe –1.2
Side lobe level
in dB y-z Plane –12.0 –2.8
directional and side lobe is observed in x-z plane. This
may be due to presence of metallic plate which signifi-
cantly reduces the power radiated towards back side of
the plate. No side lobes observed in y-z plane
From Figure 5 and Table 1 it can be seen that the ra-
diation pattern of the antenna in x-y plane is
omni-directional and side lobes are observed in both x-z
and y-z planes. This may be attributed to wave reflec-
tions due to abrupt changes in the media when antenna is
in direct contact with the bio-medium.
From Table 1 it can be seen that when proposed an-
tenna is in direct contact with phantom muscle layer at
5.156 GHz, the values of gain, directivity, total effi-
ciency and 3-dB Beam-width of the proposed antenna
reduce in comparison to those found for free space.
(a)
3.3. SAR Evaluation
The origin is selected on the top surface of ground plane
coinciding with the central line of dual segment RDRA
as shown in Figure 6. The simulation of SAR distri-
(b)
(c)
Figure 6. Geometry of modified DSRDRA with muscle
layer. Figure 7. SAR (10 g) variation in muscle layer due to modi- fied DSRDRA (a) with x-axis; (b) w ith y-axis; (c) with z-axis.

382 R. K. GANGWAR ET AL.
(a)
(b)
(c)
Figure 8. SAR (10 g) variation in muscle layer due to modi-
fied DSRDRA at different antenna-to-bio-medium separa-
tions along (a) x-axis; (b) y-axis; (c) z-axis.
compiled from the available literature [15] are 49.399,
4.2156 S/m at 5.156 GHz and 51.678, 2.3944 S/m at 3.31
GHz respectively.
The three parameters of importance for obtaining the
volume of the tissue absorbing significant amount of
power are SAR, effective field size (EFS) and penetra-
tion depth. The EFS is defined as the area enclosed
within the 50% SAR contour inside the tissue. The pene-
tration depth is the depth at which SAR becomes 1/e2
of its
value at the surface [14]. The maximum SAR (10 g), EFS
and penetration depth in the bio-medium due to the dual
segment RDRA extracted from Figure 7 are shown in
Table 2.
From Figure 7 and Table 2, it can be observed that
Table 2. SAR performance of modified DSRDRA in muscle
layer.
Parameters At 3.31 GHz At 5.156 GHz
0.2 W 1.76519 W/kg 5.05809 W/kg
Maximum
SAR (10 g) 0.02 W 0.176519 W/kg 0.505809 W/kg
Effective Field Size 31.6 × 28.81
mm2
35.71 × 28.57
mm2
Penetration Depth 23.03 mm 18.28 mm
maximum value of SAR (10 g) increases with frequency
and the values of penetration depth reduce with increase
in frequency. The trend of changes in EFS and penetra-
tion depth in phantom muscle layer may be due to in-
crease in the conductivity of the bio-medium with fre-
quency and frequency dependent characteristics of the
proposed antenna. Asymmetry is observed in SAR (10 g)
distribution along x-direction. This may be due to metal-
lic plate which significantly reduces the power radiated
towards back side of the plate and spurious radiation
from monopole coaxial probe which is also located along
x-axis.
From Figure 8, it can be observed that the value of
SAR (10 g) in muscle layer decreases as the separation
between muscle layer and antenna increases. This de-
creasing trend in the value of SAR (10 g) with increasing
antenna-to-bio-medium separation is obvious due to
greater beam divergence at larger separation. Also, the
shape of SAR (10 g) distribution changes to a great ex-
tent with increase in antenna-to-bio-medium separation
due to more beam divergence. From Figure 8 the pene-
tration depth for antenna-to-bio-medium separations of d
= 50 mm, 100 mm and 200 mm are found to be 47.11
mm, 42.91 mm and 123.96 mm respectively. Also,
asymmetry is observed in SAR (10 g) distribution along
x-direction. This may be due to metallic plate which sig-
nificantly reduces the power radiated towards back side
of the plate.
The effect of reduction in power input to the antenna
from 0.2 to 0.02 W on maximum SAR (10 g) value has
also been investigated and the results are presented in
Table 2. It is noted from Table 2 that maximum value of
SAR (10 g) in muscle layer reduces in proportion to the
reduction in power fed to the antenna. The EFS and
penetration depth are found to remain unchanged as an-
tenna input power is reduced.
4. Conclusions
The simulation studies of SAR distributions in a phan-
tom muscle layer due to modified DSRDRA have been
described using CST Microwave Studio simulation soft-
ware in WiMAX bands. The simulation results of reso-
nant frequency, return loss bandwidth and radiation
characteristics of the modified DSRDRA in free space

R. K. GANGWAR ET AL.
383
are compared with the results for the antenna in direct
contact with bio-medium. SAR distributions in a bio-
medium for different antenna-to-bio-medium separations
have been carried out at different frequencies of WiMAX
band. From the study it is inferred that the volume of the
bio-layer kept near the antenna absorbs significant
amount of power in WiMAX band. The value of SAR in
the bio-layer increases with frequency as well as with
reduction in antenna-to-bio-layer separation. Also, increase
in penetration depth and improvement in transverse plane
resolution in muscle layer due to the antenna been no-
ticed with reduction in frequency. The results presented
here may find potential application in wireless commu-
nication field for designing a wideband antenna/wearable
antenna and evaluating the power absorption in
bio-layers due to the antenna.
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