40120140505004

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 5, May (2014), pp. 27-35 © IAEME
27
MULTI-SEGMENT CYLINDRICAL DIELECTRIC RESONATOR ANTENNA
Ranjana Singh1
, Amit Kumar2
1
(Communication Department, Galgotias University, India)
2
(School of Electrical, Electronics & Communication, Galgotias University, India)
ABSTRACT
A novel and simple design of a wideband multi-segment cylindrical DRA which is fed by a
micro-strip line for broadband operation is proposed in this paper. The proposed structure has a
bandwidth of 2GHz from 6.5 to 8.5 GHz which is 50% of the frequency range ranging from 6 to 10
GHz having resonant frequency at 7.408GHz. Reflection coefficient(S11) at resonant frequency is -
66.01dB. Overall Gain is 5.44dB and radiation efficiency is -0.2825dB that is antenna is 93.70%
efficient. Total height of proposed structure is 10mm. This low profile antenna is suitable for
wireless systems like WLAN, WiMAX, C-Band applications. Simulation is done using CST
MICROWAVE STUDIO-10. Details of the proposed antenna and simulated results are presented
and discussed.
Keywords: Dielectric Resonator Antenna (DRA), Impedance Bandwidth (IBW), Perfect Conductor
(PEC), Radiation Efficiency, Reflection coefficient (S11), Resonant Frequency.
I. INTRODUCTION
DRAs offer primary features like compact size, light weight, and low cost. They have been
demonstrated to be practical elements for antenna applications and posses several merits including
high radiation efficiency, flexible feeding technique, simple geometry and easy coupling [1-2]. The
DRA is fabricated from low-loss dielectric materials. Its resonant frequencies are predominantly a
function of DR configuration and dielectric constant. From last few decades there is a deep interest
in antenna systems which operate at the higher frequencies [3]. Conventional metallic antennas
suffer problems like conductor losses, radiated power capabilities and major problem of fabrication
difficulties when their size is reduced to operate in a particular higher frequency band. These short-
comings can be over-come if a simply shaped DRA with few conducting surfaces is designed [4-5].
DRAs have attracted the antenna designers in microwave and millimeter wave band due to attractive
features which are mentioned above including zero conductor losses. DRAs of low dielectric
material, having dielectric constant as (4 <ߝ௥ < 100) are ideally suitable for antenna applications, so
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ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 5, Issue 5, May (2014), pp. 27-35
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that there can be compromise between size and bandwidth since dielectric constant also affects the
bandwidth, as dielectric constant decreases bandwidth increases [5-9]. DRAs are commonly
available in rectangular, cylindrical, conical and spherical geometries. The experimental
investigation of the cylindrical DRA is done by Long et al. which demonstrated that cylindrical
DRAs are capable of providing efficient radiation [10]. The radiation Q-factor of a DR antenna
depends on two factors excitation modes as well as the dielectric constant of the ceramic material. As
Q-factor increases the bandwidth decreases with increasing dielectric constant [11-12]. For this
reason, DRAs of relatively low dielectric constant are almost always used in antenna applications
[13].From few decades a substantial amount of research has been done to study about DRAs. It has
been demonstrated that rectangular, hemispherical, half-split cylindrical and equilateral triangular
shapes can be designed to radiate efficiently through proper choices of feeding technique and
position [13-14]. Different types of feeding techniques such as coaxial probe, micro-strip line [15],
slotted waveguide [16], dielectric image line [17] and coplanar waveguide (CPW) [18] have been
developed till now. In this paper, multi-segment cylindrical DRAs with micro- strip fed is proposed.
The proposed structure has matching bandwidth of 50%.
II. THEORY
To design DRA resonant frequency is one of the important parameter. The approximate
calculation of resonant frequency for the TM01δ mode and HE11δ mode for conventional cylindrical
DRA can be done by following expressions (1) and (2).
݂௥ ൌ
௖
ଶగ௔ඥఌೝାଶ
ට3.83ଶ ൅
గ௔
ଶ௛
…. (1)
݂௥ ൌ
଺.ଷଶସ
ඥఌೝାଶೌ ൜0.27 ൅ 0.36
௔
ଶ௛
൅ 0.02 ቀ
௔
ଶ௛
ቁ
ଶ
ൠ …. (2)
Where a is radius and h is height of antenna. The resonant frequency of the TM01δ modes of
conventional cylindrical DRA can be estimated using the transcendental equations derived from a
waveguide model [19]. The first subscript 0 in the notation TM01δ states the order of the Bessel
functions of the first and second kind which must be used to calculate the resonant frequency of that
mode, the second subscript 1 in the designation of the mode denotes the order of magnitude of the
root which is used to calculate the resonant frequency, the third subscript ߜ is merely a coefficient in
the argument of a trigonometric function which enters into the expressions for the electric and
magnetic fields inside the cavity [19]. The resonant frequency is estimated using a simple waveguide
mode of a magnetic wall. Wave numbers are calculated using equations (3), (4) and (5) [20]:
݇௫ ൌ
௠గ
௔
…. (3)
݇௬ ൌ
௡గ
௕
…. (4)
݇௭ tan ቀ
௛௞೥
ଶ
ቁ ൌ ඥሺߝ௥ െ 1ሻሺ݇௢
ଶ
െ ݇௭
ଶ
) …. (5)
Where݇௫, ݇௬ and ݇௭ are wave-numbers in x, y and z directions respectively and ݇௢ denote wave-
number in free space, defined as:
݇௢ = (2πfo)/c …. (6)

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 5, May (2014), pp.
The cylindrical DRA is characterized by their height, radius and dielectric constant,
one degree of freedom (aspect ratio radius/height), which determines
dielectric constant [19]. Impedance bandwidth is calculated using equation:
fh-fl
IBW =
fc
Where fh, fl, fc are higher, lower and cutoff frequency respectively. Voltage standing wave ratio
(VSWR) is a measure of how much power is reflected back to the input port or how perfectly
antenna is matched to transmission
reflection coefficient or return loss [18
III. ANTENNA CONFIGURATION
Proposed structure is a multi
materials GALLIUM ARSENIDE, ROGERS RT5880 and ROGERS RO3010. Individual
segment has radius of 5mm. DR is placed over a substrate made up of material ESL 41110
Antenna is excited using micro-strip
calculator. This whole structure is mounted over a ground plane
thickness l=2mm. Substrate is nothing but
proposed structure is shown in Fig. 1.
Figure 1: Final design of proposed m
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976
6472(Online), Volume 5, Issue 5, May (2014), pp. 27-35 © IAEME
29
The cylindrical DRA is characterized by their height, radius and dielectric constant,
(aspect ratio radius/height), which determines k0 and Q-factor for
Impedance bandwidth is calculated using equation:
…. (7)
are higher, lower and cutoff frequency respectively. Voltage standing wave ratio
antenna is matched to transmission line. VSWR is defined as VSWR= (1+Γ) / (1
18-20].
ANTENNA CONFIGURATION AND DESIGN
Proposed structure is a multi-layered structure designed using three cylindrical segments of
materials GALLIUM ARSENIDE, ROGERS RT5880 and ROGERS RO3010. Individual
has radius of 5mm. DR is placed over a substrate made up of material ESL 41110
strip fed whose dimensions are calculated using CST line
calculator. This whole structure is mounted over a ground plane which is made up of PEC
. Substrate is nothing but insulation between micro-strip and ground. Final
structure is shown in Fig. 1.
(a)
(b)
proposed multi-stack cylindrical DRA (a) 3D view (b) side view
© IAEME
The cylindrical DRA is characterized by their height, radius and dielectric constant, offering
factor for a given
are higher, lower and cutoff frequency respectively. Voltage standing wave ratio
) / (1-Γ), where Γ is
designed using three cylindrical segments of
materials GALLIUM ARSENIDE, ROGERS RT5880 and ROGERS RO3010. Individual cylindrical
has radius of 5mm. DR is placed over a substrate made up of material ESL 41110-7C.
CST line impedance
which is made up of PEC having
strip and ground. Final
(a) 3D view (b) side view

30
Thickness of micro-strip line (h) is 1.28mm and width of 2mm. Substrate is of thickness (t)
2mm and have same length & width of 20mm. Properties of materials used for cylinders and
substrate are:
• Cylinder 1- Have thickness (t1) 3mm made of Rogers RO3010 is a loss-free, normal type
material having dielectric constant of 10.2. Permeability µ= 1 and thermal conductivity of 0.66
W/K/m.
• Cylinder 2- Have thickness (t2) 2mm, made of Rogers RT5880 is a loss-free, normal type
material having dielectric constant of 2.2. Permeability µ = 1 and thermal conductivity of 0.2
W/K/m.
• Cylinder 3- Have thickness (t3) 5mm, made of material Gallium Arsenide, it is also a loss-free
normal type material having dielectric constant of 12.94, Permeability µ = 1 and thermal
conductivity of 54 W/K/m. It has Young’s modulus of 85 kN/mm2
, Poisson’s Ratio of .31 and
thermal expansion of 5.8 1e-
6K.
• Substrate- ESL 41110-7C is also a loss-free, normal type material having dielectric constant of
4.5. Permeability µ = 1 and thermal conductivity of 3 W/K/m.
IV. SIMULATED RESULTS AND PARAMETRIC DISCUSSION
A. SIMULATED RESULTS
The structure has been simulated and S-Parameter is shown in Fig. 2, we have a resonant
frequency at f=7.408GHz with a bandwidth of 2 GHz ranging from 6.5 to 8.5 GHz (where S11<-10
dB). The maximum return loss is up to-66.01dB at the resonant frequency. The return loss, S11 (in
dB) is shown in Fig. 2 where we can clearly see the maximum dip is at 7.408GHz.
Figure 2: Representation of S11-Parameter.
The Far-field radiation pattern at resonant frequency 7.408GHz is shown in Fig. 3 which
shows that maximum gain of antenna is 5.44 dB.

31
Figure 3: 3D view of Simulated far field radiation pattern
Fig. 4 and Fig. 5 are representing the simulated 3D Electric field radiation pattern and
Magnetic field radiation pattern respectively at resonant frequency 7.408 GHz.
Figure 4: E-Field distributions at resonant frequency 7.408GHz
Figure 5: H-Field distributions at resonant frequency 7.408GHz
Polar plot of Far-field radiation is shown in Fig. 6(a), (b) respectively to show the variation
with change in Theta and Phi. Fig. 6(a) is representing Electric monopole structure created as it is
centrally excited and its main lobe direction is 27 degree and its magnitude is 5.4 dB. Fig. 6(b) is
representing Horizontal Magnetic Dipole whose main lobe direction is 0.0 deg. and its magnitude is -
101.7 dB.

32
(a)
(b)
Figure 6: (a) E-Plane (Electric Monopole), (b) H-Plane (Horizontal Magnetic Dipole)
Figure 7: VSWR for proposed DRA.
The simulated VSWR of proposed multi-layered DRA is shown in Fig. 7. The matching
frequency range is from 6.5 to 8.5 GHz where the VSWR < 2 and return loss (S11) < -10 dB.

33
B. PARAMETRIC DISCUSSION
To verify that the proposed structure has best results at optimum parameters, some of the
parameters are varied (keeping others constant), results are simulated and compared and are
presented in tabular form. Fig. 8 and Table I show that maximum bandwidth is 2GHz when radius of
antenna is 5mm keeping other parameters constant. Fig. 9 and Table II represent that maximum IBW
and bandwidth is when dielectric constant is 12.94.
Figure 8: Variation of S-Parameter with variation in radius(r in mm) of DR
TABLE I: S11-parameter and Impedance bandwidth at different Radius of DR
Radius(of all three
cylinders) in mm
Reflection
coefficient (dB)
Bandwidth ( GHz) Resonant
frequency
(GHz)
IBW
(%)
3 - - - -
4 -50 1.6 8.75 18.2
5 -66.01 2 7.408 27
6 - - -
7 -25 - 8.46 -
Figure 9: Variation of S-Parameter with variation in (epsilon) Dielectric constant

34
TABLE II: S11-parameter and Impedance bandwidth at different Dielectric Constants
Epsilon Reflection
coefficient (dB)
Bandwidth ( GHz) Resonant
frequency (GHz)
IBW
(%)
8.94 -18 2 8.75 22
10.94 -25 2 7.75 25
12.94 -66.01 2 7.4 27
14.94 -29 1.75 7.1 24
16.94 -23 1.65 6.8 24
IV.CONCLUSION
The multi-segment cylindrical DRA, which provides wide bandwidth in WiMAX and WLAN
has been proposed in this paper. The radiation characteristics and reflection coefficient of the
proposed antenna are evaluated through simulation studies using CST Microwave Studio 10. By
investigation and analysis it is inferred that the bandwidth of the proposed antenna is found to be
50% which covers 7.4 GHz WiMAX band. Advantage of proposed antenna is that it is a low profile
antenna with simple design steps. Overall gain of antenna is 5.44 dB and total efficiency of -0.2825
dB at resonant frequency 7.408GHz.
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