EuMC_2011 - iitk.ac.in - Indian Institute of Technology Kanpur

Coaxial Fed Half-Split Multilayer Cylindrical
Dielectric Resonator Antenna for Wideband
Applications
Raghvendra Kumar Chaudhary 1 , Gautam Kumar Singh 2 , Kumar Vaibhav Srivastava 3 and Animesh Biswas 4 .
Department of Electrical Engineering
Indian Institute of Technology Kanpur
Kanpur, Uttar Pradesh, INDIA, 208016
Phone No: +91-512-2597319
Abstract—In this paper a wideband half-split multilayer
cylindrical dielectric resonator antenna (MCDRA) fed through
coaxial probe is developed and discussed. The concept of multi
layers is introduced in half-split dielectric resonator antenna for
getting wide bandwidth. The design parameters of an antenna
such as arrangement of dielectric layers, probe height and DR
aspect ratio are investigated. The proposed multilayer
cylindrical dielectric resonator antenna is excited with TM 21δ
mode. The proposed structure provides ~60% impedance
bandwidth for input reflection coefficient (S 11) below -10 dB with
total gain of 6.09 dB.
Keywords- Dielectric Resonators (DRs), Dielectric resonator
antenna (DRA), wideband antenna, TM 21δ mode, impedance
bandwidth, gain.
I. INTRODUCTION
Due to number of attractive features of DRA such as low
loss, wide-bandwidth, high gain, versatility in their shape and
simple feeding mechanism, numerous investigations have
been carried out on DRAs in last two decades [1].
In past, DRs were usually treated as an energy storage device
and mainly used in microwave filters and oscillators rather
than as a radiator or antenna. When DR is placed in open
environment then Q-factor reduced significantly and DR act
like an antenna because power is lost in radiated fields [2].
The first experimental research is carried out for wideband
DRA in 1989 by Kishk et al.. The input impedance of stacked
cylindrical dielectric resonator antennas is investigated
experimentally and the dielectric resonators made of different
materials have achieved the bandwidth of 25% [3]. The
Multilayer Cylindrical DRA (MCDRA) approach has also
been reported by commercially available materials [4]. The
multilayer multi-permittivity approach has been studied for
higher mode separation in dielectric resonator in microwave
integrated circuit (MIC) environment [5]. The multilayer
concept has also introduced in the three elements MCDRA
for getting wide input impedance bandwidth [6].
In this paper, we have introduced the multilayer concept of
dielectric layers in half-split DR as shown in Fig. 1 for
Proceedings of the 41st European Microwave Conference
{ 1 raghav, 2 singhgk, 3 kvs, and 4 abiswas}@iitk.ac.in
increasing the impedance bandwidth of antenna. The TM21δ
mode is excited in DR antenna. The input reflection
coefficient (S11) and absolute gain patterns and of proposed
structure are simulated using the Ansoft’s High Frequency
Structure Simulator (HFSS), which is a finite-element method
based commercial software package.
Multilayer
half-split
cylindrical DRA
Coaxial
Probe
Figure 1. Geometry of proposed wideband half-spilt multilayer dielectric
resonator antenna (a). 3D view (b). top view (c). Front view (XX’).
(a)
ß
(b)
(c)
(a)
X X’
978-2-87487-022-4 © 2011 EuMA 1015
10-13 October 2011, Manchester, UK
a

II. THEORY FOR CONVENTIONAL HALF-SPLIT DRA
For the simple half-split dielectric resonator antenna with
sector angle β, radius a and height h, the z-component of
z
electric field distribution for the TM vpm+
δ mode inside the
DRA is given by cavity model analysis [7, 8]
( ) cos ( φ ) cos(
)
vpm
z v r z
E = AJ k r v k z
(1)
for 0 ≤ r ≤ a,
0 ≤φ≤ β , 0 ≤ z ≤ h . In the above expression v
is a positive real number, depends upon the boundary
conditions while p, m are positive integers and k r , kz are the
wave numbers. The function J v denotes the vth-order Bessel
function of first kind and A is complex constant depends upon
the geometry and feed.
The resonant frequency of a mode f vpm is given as [7, 8]
c
f = k + k
(2)
vpm
2 2
r
2πaεr
r z
X vp (2m + 1) π
where c is the velocity of light, kr
= , kz
= are
a 2h
wave numbers and X vp is the root of characteristic equations.
For a sector DRA with sector angle β = π with open sector
faces, the fundamental resonant mode is TM11δ and the next
higher resonant mode is TM 21δ
[9]. The fractional impedance
bandwidth of a DRA can be calculated by
Δf
Impedance Bandwidth ( BW ) = (3)
f
where Δ f and f r are absolute bandwidth and resonant
frequency respectively.
III. ANTENNA CONFIGURATION
Fig. 1 shows the proposed half-spilt multilayer cylindrical
dielectric resonator antenna where the height of layers are
h1, h2 and h3 and their dielectric constant are εr1, εr2 and εr3
respectively. The radius of each layer is a. The MCDRA is
placed on metallic ground plane and this arrangement is
excited with TM21δ mode by coaxial probe of height hp and
radius ro.
A. Dielectric Layer Optimization
The MCDRA consists of several layers having different
heights and pemittivitties, but they need to be arranged in
some particular manner for wide impedance bandwidth. The
different arragnemnts of MCDRA have been simulated and it
has been found that if layers are arranged in ascending order
of their permittivttives, the bandwidth can be improved
signinicantly. It is also obvious that if lower permittivity layer
is on bottom side the less amount of energy will be confined
r
in bottom layer and effect of ground plane to the fields stored
in that layer will be minimal. However, if the permittivity of
top layer is higher, most of the energy will confined in top
layer and will be and less influenced by ground plane.
The optimized dimensions for half-split multilayer cylindrical
DRA are obtained as the radius of each dielectric layer (a) =
20 mm, height of bottom layer (h1) = 3.81 mm, height of
middle layer (h2) = 3.17 mm and height of top layer (h3) =
3.81 mm. The dielectric materials are choosen as from
commercailly available materials Polyflon Polyguide ( ε r =
2.32), Roger RT/Duroid 6006 ( ε r = 6.15), Roger RT/Duroid 6010
( ε r = 10.2).
TABLE I. IMPEDANCE BANDWDITH OF DIFFERENT DIELECTRIC LAYER
ARRANGEMENT
[a = 20 mm, h1 = 3.81 mm, h2 = 3.17 mm, h3 = 3.81 mm, ro = 0.55 mm.]
Bottom
Layer (εr1)
Middle
Layer (εr2)
Top Layer
(εr3)
Probe
height (hp)
BW (%)
6.15 10.2 2.32 10.6 mm 23.1
10.2 6.15 2.32 8.2 mm 12.3
6.15 2.32 10.2 8.8 mm 51.7
2.32 6.15 10.2 7.7 mm 60.0
10.2 2.32 6.15 10.4 mm 35.5
2.32 10.2 6.15 6.4 mm 50.2
All the possible dielectric layer arrangement for half-split
MCDRA and probe height for different arrangement
corresponds to its optimal height for maximum bandwidth is
listed in Table I. So the optimal arrangement for three
dielectric layers from bottom to top are Polyflon Polyguide
( ε r1
= 2.32), Roger RT/Duroid 6006 ( ε r 2 = 6.15), Roger
RT/Duroid 6010 ( ε r3
= 10.2). Using this combination wide
impedance bandwidth can be obtained.
1016
By the simulations, it is clear that the impedance bandwidth
will be high when the top layer having high dielectric
constant in comparision with other layers. For multilayer
DRA, lower dielectric constant section improves the
bandwidth and higher dielectric constant section helps to
lower the resonant frequency and vice-versa [2].
B. Probe Height Optimization
Now for studying the characteristics of proposed half-spilt
multilayer dielectric resonator antenna, the study has been
performed for different probe height for good input
impedance matching.
Fig. 2 shows the comparision of input reflection coffecient
(S11) for proposed half-spilt multilayer cylindrical dielectric
resonator antenna with different probe heights. From the Fig.
2, it is clear that the wideband response and good matching
occurs at probe height of 7.7 mm.

Reflection Coefficient (S 11 ) dB
-30
hp = 7.1 mm
hp = 7.3 mm
hp = 7.5 mm
-40
hp = 7.7 mm
hp = 7.9 mm
hp = 8.1 mm
-50
3 4 5 6
Frequecny (GHz)
7 8
Figure 2. Simulated reflection coefficient (S11) of half-spilt multilayer
dielectric resonator antenna for different probe heights.
IV. RESULTS
The design parameters of half-spilt multilayer cylindrical
dielectric resonator antenna are a = 20 mm, h1 = 3.81 mm, h2
= 3.17 mm, h3 = 3.81 mm, ro = 0.55 mm, and hp = 7.7 mm.
The input reflection coefficient (S11) below -10 dB is obtained
in the frequency range of 4.14 to 6.94 GHz. The resonance
frequency is 4.68 GHz and correspondingly the percentage
impedance bandwidth is ~60% as shown in Fig. 3.
Reflection Coefficient (S 11 ) dB
0
-10
-20
0
-10
-20
-30
-40
4.14 GHz
4.68 GHz
6.94 GHz
-50
3 4 5 6
Frequecny (GHz)
7 8 9
Figure 3. Reflection coefficient (S11) of half-spilt multilayer dielectric
resonator antenna. [a = 20 mm, h1 = 3.81 mm, h2 = 3.17 mm, h3 = 3.81 mm,
ro = 0.55 mm, εr1 = 2.32, εr2 = 6.15, εr3 = 10.2 and hp = 7.7 mm]
The VSWR of half-split multilayer cylindrical DRA is shown
in Fig. 4. The VSWR < 2 is observed in the frequency range
4.14 GHz to 6.94 GHz.
The input impedance of the antenna is shown in Fig. 5, which
indicates good matching with the coaxial feed line at
resonance frequency 4.68 GHz. The real part of input
impedance is 50.47 ohm and imaginary part is 0.46 ohm at
resonance frequency.
1017
VSWR
3 4 5 6 7 8 9
Frequecny (GHz)
Figure 4. VSWR for half-spilt multilayer dielectric resonator antenna.
R in , X in (Ohm)
Figure 5. Input impedance (real and imaginary part) of half-spilt multilayer
dielectric resonator antenna.
0
Gain (dB)
30
25
20
15
10
5
0
150
125
100
75
50
25
5
0
-5
-10
-15
270
-15
-10
-5
0
5
0
-25
-50
-75
300
240
VSWR < 2 for frequency range 4.14 GHz to 6.94 GHz
at 4.68 GHz
R in = 50.47 ohm
X in = 0.46 ohm
3 4 5 6
Frequency (GHz)
7 8 9
330
210
180
30
150
60
120
Figure 6. Absoulte gain pattern (at 4.68 GHz) in x-z plane for half-spilt
multilayer dielectric resonator antenna.
Fig. 6 and Fig.7 shows the Absoulte gain pattern of half-split
multilayer cylindrical DRA for the far field in the two
principal planes, i.e. absolute gain versus θ for Φ = 0 o (x-z
90

plane) and absolute gain pattern versus θ for Φ = 90 o (y-z
plane) at resonanace frequency of 4.68 GHz.
Gain (dB)
10
5
0
-5
-10
300
-15
270
-10
-5
0
240
5
10
330
210
0
180
30
150
60
120
Figure 7. Absoulte gain pattern (at 4.68 GHz) in y-z plane for half-spilt
multilayer dielectric resonator antenna.
Figure 8. Absoulte gain in 3D (at 4.68 GHz) for half-spilt multilayer
dielectric resonator antenna.
The far field, 3-D view of total gain pattern of proposed
struture is shown in Fig. 8, which shows the maximum gain
of 6.09 dB at the resoanace frequency of 4.68 GHz.
V. CONCLUSION
A half-split multilayer cylindrical dielectric resonator antenna
mounted on finite ground plane has been investigated. It is
simply excited by coaxial probe with TM21δ mode. The
concept of stacking the dielectric layers in half-split DRA is
proposed in this paper for getting the wide input impedance
bandwidth. The input reflection coefficient (S11) curve shows
~60% impedance bandwidth (S11 < ─10dB) with good
radiation pattern which is stable in the passband. The
90
1018
maximum absolute gain of proposed antenna is 6.09 dB at
4.68 GHz. The proposed antenna is suitable for C-band
application like in WiMAX applications.
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