Embedded Dual band Cylindrical Dielectric Resonator Antenna

doi:10.4236/ijcns.2011.410080

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Int. J. Communications, Network and System Sciences, 2011, 4, 656-661

doi:10.4236/ijcns.2011.410080 Published Online October 2011 (http://www.SciRP.org/journal/ijcns)

Embedded Dual-band Cylindrical Dielectric

Resonator Antenna

Ahmed Benomar1, Noureddine Boukli Hacene2, Hicham Megnafi3, Patrick Vaudon4

1,2,3Department of Telecommunication, University of Abou Bakr Belkaïd, Tlemcen, Algeria

4XLIM Laboratory, OSA Department , Université de Limoges, Limoges, France

E-mail: [email protected], boukl i n @yahoo.com, megnafi.hi ch am @ gm ail .co m, [email protected]

Received July 26, 2011; revised August 15, 2011; accepted September 8, 201 1

Abstract

A compact dual-band antenna made of high dielectric constant substrate is studied. Embedding a higher di-

electric cylindrical inside the substrate host cylindrical enhances the dual-band behaviour. The first part dis-

plays the characteristics of single CRDA as return loss, bandwidth and radiation pattern, then, the second

part describes the aim of using an antenna, composed by the arrangement of two cylindrical resonators in

which the smallest is inserted in the largest, to lead dual-frequency behaviour, and achieve a dual-band an-

tenna. The proposed antennas are investigated using Finite Element Method (FEM), the impedance matching

dual-band definition and covers the Ultra High Frequency band (UHF).

Keywords: Dual-band Antenna, Bandwidth, Return Loss, UHF, DCS

1. Introduction

The dielectric resonator antennas (DRAs) have attracted

wide attentions in various application s, as armored filters

or oscillators [1,2], They offer several advantages in

terms of high radiation efficiency and Q factor. Indeed,

when a resonator is placed in a cavity, it presents a high

quality factor, which allows the realization of a highly

selective filter.

DRAs topologies as rectangular, cylindrical, hemi-

spherical, circular, triangular etc. are possible with vari-

ous feed techniques, for a single-mode excitation, the

DRA’s bandwidth doesn’t exceed 15%. Recently, dif-

ferent shapes and embedded resonators have been pro-

posed to enhance the bandwidth; these techniques are

generally difficult to implement without increasing the

size of the antenna. In another way the resonant fre-

quency of the DRA is predominantly determined by its

size, shape and material permittivity (r



) [1,2].

In this present work, a novel DRA design is proposed,

and a parametric study is carried out. In the first section,

the proposed cylindrical dielectric resonator (CDR) an-

tenna shown in Figure 1 is made from ceramic 1r



36.7 mm, a1 = 12.65 mm and d1 = 9.6 mm and excited by

a coaxial probe is inve stigated; the study next focuses on

new way of designing a dual-band, symmetrical structure

and low profile DRAs, in which a smaller size dielectric

resonator is embedded in a larger size “host” dielectric

resonator with a lower dielectric constant as shown in

Figure 9.

The operation principles of these embedded DRAs are

similar to the stacked DRA but it has the advantage of

being low-profile. Since the structure consists of same

DRs with different dielectric constants, there are two

resonant frequencies that can be made either close to

each other to yield wideband behaviour, or sufficiently

far apart to yield dual-band behaviour.

In order to design and optimize the proposed antenna,

finite element method and Eigen mode solver are used.

The measurement and simulation results are shown, fol-

lowed by a dis cuss i o n.

2. CDRA Theory

The preferable mode for the filter design is the mode

TE01δ because of its high Q factor performance, while for

dual-band radiating purposes TM01δ mode is chosen for

its Omni-directional pattern and HEM11δ mode is chosen

for its broadside radiation [3,4]. The cylindrical resonator

antenna under investig ation have height and radius d and

a, respectively. The ground plane, assumed to be of finite

extent, supports the dielectric cylinder. The simple way

of excitation of the lowest mode of the structure which is

the HEM mode is using a coaxial probe, vertically orien-

A. BENOMAR ET AL.657

tated with height equal to h and located at distance equal

to ρ far from the centre of DRA on phi = 0˚, the charac-

teristics of the CDRA can be written as [1].

2.1. Resonant Frequency

The resonant frequency of the cylindrical DRA was cal-

culated approximately with (1) described in [1]. This

gives a frequency of 1.96 GHz for the single CDR (with



= 36.7, diameter a1 = 12.65 mm and high d1 = 9.6

mm). In practical applications, we are interested in the

fundamental (dominant) mode, which has the lowest

resonant frequency.

The resonant frequency is given by dielectric constant



, radius a, and height d on Equation (1) and the value

are in Table 1 [1,4],

02.208 1 0.70130.002713

fdd





 





 

  





(1)

Equation (1) is u sed only when 0.4 6







 [1,2],

where c is the velocity of light in free space and r



the relative dielectric constant of the cylinder.

2.2. Field Distributions

By viewing the field distribution within the DRA, one

first may understand the mode in which the DRA is

resonating, and secondly may be able to make adjust-

ments to the DRA shape, size, and probe position to

maximize operation in the required mode. Being able to

view these fields also helps in understanding the ex-

pected radiation pattern and how modification to the

structure will influence the pattern. To examine only

those fields due to one resonant mode within the DRA,

the excitation must be at one frequency only [1,5].

The ideal radiation pattern (far-field pattern) of the

mode TM01δ looks like a pattern of a quarter-wavelength

monopole above the ground plane. The radiation pattern

of the HEM11δ mode looks ideally like a pattern of the

half-wave dipole parallel to the ground plane [1]. In

practice, the feeding mechanism may excite more than

one mode, so that the pattern will not look like the ideal

one. Furthermore, the ground plane will be of finite ex-

tent, which will cause the p attern to depart from an ideal

one and there will be some radiation to the lower

half-space [4,5]. All these effects are taken into account

in the numerical simulation.

3. Principles of Investigation

(a)

(b)

Figure 1. DRA configurati; (b) 3-D view.

Table 1. Frequencies of the tw o configurations.

on. (a) Side view

Configuration Freq (eigen mode Permittivit

antenna solver) (1r



;2r



)

Single DRA 136.7 .94 GHz

D 360 RA embedded1.71 GHz .7 + 9

omprises a single CDR fabricated by using ceramic c

dielectric materials with relative permittivity 1r



= 36.7

with diameter a1 = 12.65 mm and high d1 = 9m. The

DR is fed energy by a 50Ω Coaxial line of width r = 0.65

mm and length h = 5.6 mm at position ρ = 11.56 mm. “In

all sections, the coaxial-probe line is localized in the

edge near to the wall of CDR to maximize the excitatio n

of the dominant mode”.

The proposed structure

.6 m

in Figure 1 is performed and

.1. Antenna Composed by Single CDR

this first part, Figure 2 shows the propo sed DRA con-

e results are given by software based on finite elements

method; the investigation is subdivided into three parts

as following.

figuration using one single cylindrical dielectric resona-

tor fixed on finite ground plane with dimension men-

tioned above is lead to shows the adaptation in term of

return loss and radian pattern.

The configuration of proposed DRA depicted in Figure 1.

A. BENOMAR ET AL.

658

Figure 2. Geometry of the probe-fed cylindrical DR.

It is clearly noticed from Figure 3 and Figure 4, that

good

y Two DRA Delta = 0

drical element has a radius a2 = 7.3

e resonant frequency of the HEM11d mode of a cylin-

drical dielectric is about 1.91 GHz with reflection coeffi-

cient S11 = –50 dB. The simulation results are obtained

from Fidelity using a finite elements method and show-

ing good agreement with calculated (in Table 1).

By incorporating a suitable feed position, and

obe lentgh ,the radiations patterns E-phi and E-theta

over the two orthogonal planes (E-plane and H-plane)

are having broadside direction and nearly ideal because

some higher order modes with non-broadside radiation

patterns are excited and disturb th e radiation p attern axial

symmetry [6,7].

3.2. Antenna Composed b

Besides the single DRA, embedded DRAs can be of di

ferent shapes, such as cylindrical, square, or elliptical

shapes [8-11]. For this purpose study, the geometry of

embedded element is same as the host resonator as

shown in Figure 5.

The additional cylin

m, high d2 = 5.6 mm, and permittivity 2r



= 90. By

using Eigen mode solver the frequency of embedded

antenna is 1.71 GHz as in Table 1.

Figure 3 and Figure 6 show the s

the

imulated reflection

ly to the permittiv-

ity

but

RA and embedded

efficients of the single and embedded resonator re-

spectively it is clearly found that no dual-band behaviour

and also one frequency mode. So the new antenna looks

like a single antenna ch aracteristics.

The frequency is not proportionate

which means that the first frequency mode of the

embedded antenna is lowest then the single antenna.

Then we notice the apparition of the second mode

ith low return loss value (< –10 dB) at f2 = 2.1 GHz. It

means that it should be possible to design the antenna

either for wideband or for dual-band operations by vary-

ing the dielectric constants and geometry parameter to

increase the second frequency f2 [9].

The radiation pa t t ern of t he singl e D

Figure 3. Computed return losses of the DR antenna

against frequency. a = 12.65 mm, d = 9.6 mm, ρ = 11.75 mm,

h = 5.5 mm, r = 0.65 mm, GND = 75 × 75 mm.

Figure 4. Simulated radiation patterns of the single cylin-

drical DRA.

Figure 5. Geometry of the CDRA.

DRA are the same and present broadside looks as shown

y Two DRA Delta ≠ 0

in Figure 7; finally the two antennas behave the same

characteristics.

3.3. Antenna Composed b

In this section, we provide some insight into dual-ban

A. BENOMAR ET AL.

659

Figure 6. Computed return losses of the CDR antenna

against frequency. a1 = 12.65 mm, a2 = 7, 3 mm, d1 = 9.6mm,

d2 = 5.6 mm, ρ = 11.75 mm, h = 3 mm. Figure 8. Geometry of the CDRA.

behaviour. For this purpose, two cases are studied [8-10].

First, see the impact of varying only the distance

“Delta” between the two cylin drical centre is varied from

1 mm to 5.35 mm (a1-a2) as shows in Figure 8, In the

second case we keep the same configuration and the

permittivity of the host cylindrical DR is fixed (1r



36.7) while that 2r



of the embedded element is varied

from 30 to 90 with step equal to 10.

The Figure 9 and Figure 10 show the return losses for

these two cases. In case 1, as shown in Figure 9, when

the cylindrical resonators are offset by Delta ≠ 0, it ap-

pears more resonance peaks. This phenomenon seems to

prove that this configuration of dielectric resonators be-

haves either as an equivalent resonator “Delta = 0”, but

as two different singles resonators.

Figure 7. Simulated radiation patterns of th e double CDRA.

Figure 9. Effect of varying Delta from 1 mm to 5.35 mm.

A. BENOMAR ET AL.

660

Figure 10. Effect of varying embedded element permittivity (2r



) from 30 to 90

Figure 11. Computed return losses of the CDR antenna against frequency. a1 = 12.65 mm, a2 = 7, 3 mm, d1 = 9.6 mm, d2 = 5.6

In effect, by increasing Delta and feed the internal

wo frequencies modes with a

= 2.1 GHz [9].

When Delta increases the second mode becomes more

trical. So it is important to choose the

07 GHz.

mm, ρ = 11.75 mm, h = 3 mm, r = 0.65 mm, GND = 75 × 75 mm.

sonator the fields’ lines are forced not to behave a dis-

play as a single resonator.

This structure has now t

aximum radiation diagram in the axis (θ = 0˚) of which

the first frequency is lower than the external resonator

and the second is greater than that embedded resonator.

In addition to this second mode, it aparts a mode whose

caused a hollow in axis (θ = 0˚) of radiation pattern at f2

adapt, and the radiation diagram over the two planes be-

comes dissyme

edium delta to keep the ideal performance.

For Delta = 4.5 mm the CDRA embedded present a

good adaptation (low S11) at resonate frequency (Table 1)

the 1st mode is at 1.69 GHz and 2nd mode at 3.

Second, Figure 10 shows that when the dielectric con-

stant of the embedded element decreases, the two reso-

nance frequencies are increased at different rates. The

A. BENOMAR ET AL.661

optimized wideband performance is obtained with 2r



= 90, where two resonances are close to each other. It is

noted that the two bands are further apart as 2r



be-

come small so the gap between the 1st mode and

second become large; it means that the permittivity of the

embedded element should be chosen according the

requirement application and the dual resonances can be

achieved by adjusting the feed dimensions and delta

length and the permittivity of the an tenna.

In short, the arrangement of two resonators in which

the smallest is inserted in the largest leads to a dual-fre-

quency behavior; the geometrical charact

the

eristics of

and

the

tenna control performance. Thus, distance between the

centers of the resonators affects the adaptation, the per-

mittivity mainly affect the resonant frequencies; Indeed,

in some configurations, radiation patterns are signifi-

cantly altered. In addition, a co mpromise must always be

defined between the simultaneous adaptation of both

bands and the spacing between the bands and the purity

of radiation patterns [7-9] .

Finally the Figure 11 and Figure 12 shown the return

loss and radiation pattern respectively of the embedded

CDRA whit Delta = 4.5 mm2r



= 90.

Figure 12. Simulated rad iation patterns of th e single CDRA.

4. Conclusions

new dielectric resonator antenna has been proposed

studies have been realized to

e impact on the resonance frequencies. The results

ces

K. W. Leung, “Dielectric Resonator An-

tennas, ser. Electronic & Electrical Engineering Re-

ctric-Resonator Antenna Tech-

A in

this work; parametricsee

have shown that by embedded the dielectric antenna re-

sonance frequencies have been reduced compared to the

single DR antenna. Otherwise good performances have

been obtained. The embedded structure was achieved

using coaxial probe feeding comprise two resonators

inserted one into the other revealed dual-band behavior.

The proposed antenna can be used for UHF and/or DCS

1900 applications with a wide bandwidth and a good

efficiency.

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