DIELECTRIC RESONATOR ANTENNA - S Square Club

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16 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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THIS PRESENTATION CONSISTS OF

1.Introduction

2.Purpose of DRA

3.Structure of DRA

4.Excitation methods

5.Radiation patterns

6.Factors effecting the Resonant frequency

7.Challenges

8.Conclusions

9.References

INTRODUCTION


The field of wireless communication has been under
going a revolutionary growth in the last decade
.


2G
-
cellular communication (portable mobile phones)



3G
-

Bluetooth, LAN


The crucial component of a wireless network is the

Antenna’.


In the last two decades the classes of antennas
investigated and extensively reported are



1.Microstrip patch antenna



2.Dielectric Resonator Antenna


INTRODUCTION TO DRA


Since the frequency range of interest has gradually
progressed upward and the frequencies in millimeter
region(100
-
300Ghz) are employed, the conduction
losses in metallic antennas increase to such a level
that efficient operation of the systems is impaired.



So an idea to use dielectric material as a radiator was
conceived.



Dielectric resonators were used as energy storage
devices but if the cavity is not enclosed by metallic
walls the EM fields exist beyond the geometrical
boundary of the cavity.








INTRODUCTION TO DRA


The use of dielectric resonator as a resonant antenna
was proposed by S.A LONG in early nineteen eighties.



Dielectric resonator antennas offer advantages like
small size, low cost and most importantly freedom
from metallic loss.



Therefore dielectric resonator antenna have a lot of
applications in millimeter band where the conductor
loss of a metallic antenna becomes severe.


PURPOSE OF DRA


As the frequency increases conductor losses
increases and antenna efficiency will decreases
.


Conversly only losses present in the DRA are due
to imperfections in the Dielectrics which are very
small compared to conductor losses.


Dielectric resonators which we are using in
microwave applications are having (
ɛ

> 20) and
Q(50
-
500).


By choosing a dielectric material (5<

<20)
properly the radiation fields can be enhanced.





The dimension of a DRA is of the order of
λ
o/√(
ε
). Thus by
choosing high value of
ε
, the size of DRA can be significantly
reduced.



High Radiation efficiency(=95%)due to absence


of conductor losses.



High
ɛ
r

tolerance (1
-
5%)



Wide
frequency range: f = 0.7
-
35GHz

COMPARISION WITH MICROSTRIP
ANTENNA



In Micro strip radiation occurs due to narrow slots
where as in DRA radiation occurs due to whole DRA
surface.


COMPARISION WITH MICROSTRIP
ANTENNA







In Micro strip radiation occurs due to narrow slots



where as in DRA radiation due to whole DRA surface.



DRA has wider impedance bandwidth than micro
strip



DRA avoids surface waves

STRUCTURE OF DRA


The DRA consists of a ground plane and over it a
dielectric resonator is placed as shown in the figure.


The dielectric resonator can be of various shapes like
rectangular ,cylindrical , hemispherical, triangular
,spherical cap, circular ring etc


STRUCTURE OF DRA

Shapes of DRA

Some examples of Dielectric materials

Ref::1



An important parameter for DRA is its resonant
frequency


The Resonance frequency of a dielectric resonator depends on


dimensions of resonator and dielectric constant.

Ref::1



DRA size decreases as the dielectric constant increases



Wavelength of the dielectric resonator is important


because from this wave length the dimensions of


Micro strip circuit can be designed
.


The dielectric resonator antenna is a resonant circuit


that is able to store electromagnetic fields with a


minimum loss of energy within the resonator i.e. a


cavity with a high
-
unloaded quality factor, QU.

Simple design of DRA using Disk shape
dielectric


The dielectric
resonator antenna (DRA) consists of high

dielectric constant materials, high quality factors and

mounted on a grounded
dielectric


substrate of lower

permittivity.


The
selected dielectric
disk


is operating
at frequency
of 2.4
GHz


with dielectric constant of 34.73.


The
micro strip
transmission line has been used as a

feeding line for the resonator.

The magnetic fields inside a DRA




THE ELECTRIC FIELDS INSIDE A DRA

FIELDS INSIDE A RECTANGULAR
DRA

The
Hx

component of

magnetic field is dominant along the centre of
DRA , while E
-
fields (
Ey

and
Ez
) circulate around the
Hx

component.

Showing 2
-
D image of fields inside
DRA

Excitation Methods



APERTURE COUPLING


PROBE COUPLING


MICROSTRIP LINE COUPLING

Aperture coupling


This method of exciting DRA is through an aperture in
the ground plane upon which the DRA is placed.

The various types of apertures are shown

Showing aperture coupling


Micro strip line COUPLING is preferred over the
coaxial cable because it offers good impedance
matching compared to the coaxial line.


The length of the slot is chosen large enough so that
sufficient coupling exists but small enough so that it
does not resonate within the band of operation.

Aperture coupling to rectangular
DRA

Aperture coupling to cylindrical
DRA

PROBE COUPLING


This type of coupling employs a probe in order to
couple a DRA.


The probe consists of a centre pin that extends
through the ground plane.


This probe can also be soldered to a flat metal strip
which is placed adjacent to DRA.


This flat metal strip can also be modeled so that
impedance matching is achieved.

SHOWING PROBE COUPLING

COUPLING THROUGH A METAL
PLATE

PROBE COUPLING TO RECTANGULAR DRA

MICROSTRIP LINE COUPLING


A DRA can be coupled with the help of micro strip line
in two ways




1)Direct
-
coupling




2)side
-
coupling

SHOWING DIRECT COUPLING

SHOWING SIDE COUPLING

THE MULTISEGMENT DRA(MSDRA)



Q
U

refers to the Internal energy dissipation where as
the External quality factor
Q
E

refers to energy
dissipation outside .


The loaded Q,QL takes into account all causes of energy
dissipation and is given by

The experimental results
[1]

The radiation patterns for different
a/d

ratios

The radiation patterns for different

r
values

Radiation Pattern[1]


The HPBW for H
-
plane is 77.72
°

greater
than measurement,
which are 72
°
.


The HPBW for E
-
plane is 46.61
°

for
measurement and 45
°
for simulation
respectively
.

Ref:;1


There are a few factors affecting the Resonance
frequency.

1 Adhesives for Dielectric
Resonator.

2. Environment.

3. Equipment.

4. Fabrication process.

Challenges


In order to be suitable for GSM and PCS antenna,


applications
ε
r

needs
to be <30



DRAs with ε
r <30
at frequencies below 3GHz are

generally too large to be used for handsets

REFERENCES

[1] S.A Long ,M.W.McAllister and
L.C.Shen

,“The resonant
cylindrical dielectric cavity antenna ,”IEEE Transactions on
Antennas & Propagation,Vol.31,pp.406
-
412,May 1983.

[2]
Collin,R.E
. ,Foundations for Microwave Engineering, New
York: McGraw Hill,1966.

[3]
A.Petosa
, Dielectric Resonator Antenna Handbook,
Norwood,
MA:Artech

House,2007.

[4]
K.M.Luk

and
K.W.Leung
, Dielectric Resonator Antennas,
Baldock,U.K
. : Research Studies,2003.

WEBSITES:

www.wikipedia.com

www.antena
-
theory.com


Thank you….....


Any queries…….