Rectangular Dielectric Resonator Antenna with Stacked Ba

Rectangular Dielectric Resonator Antenna with Stacked Ba _x Sr _1-x TiO ₃ Ceramic film

Idris Messaoudene^1,*, Massinissa Belazzoug², Islam Bouchachi¹, Mounir Boudjerda¹, Abdelmalek Reddaf¹, and Karim Ferroudji¹,

1 Research Center in Industrial Technologies CRTI, P.O.Box 64, Cheraga 16014 Algiers, Algeria

2 Laboratoire d’Electronique et des Télécommunications Avancées, Université de Bordj Bou Arréridj, Algérie

* i.messaoudene@crti.dz Abstract— In this communication, we propose a new

dielectric resonator antenna loaded with rectangular ceramic of the BST material. The high permittivity of the material allows the shifting of the antenna resonant frequency from 10.77 GHz to 8 GHz, achieving a size reduction of the resonator antenna about 67% compared to an ordinary DRA for the same resonant frequency. The numerical analysis was carried out using two electromagnetic simulators including the CST Microwave Studio in the time domain and the HFSS (High-frequency Structure Simulator) in the frequency domain. The numerical results issued from simulations are presented and compared in terms of the resonant frequency, antenna size, reflection coefficient, and radiation patterns.

Keywords—Dielectric resonator antenna DRA, BST ceramic, Numerical analysis.

I. INTRODUCTION

In the 1970s, the dielectric resonators of a high permittivity (dielectric constant ε_r of the order 100-300) were used as resonant cavities for various passive and active microwave components including; filters, oscillators, amplifiers and tuners [1]. For the dielectric cavities with a high permittivity, the radiation losses are neglected, in this case the quality factor Q depends only on the dielectric losses. However, the decrease of the dielectric permittivity increases the amount of energy lost as radiation form, which degrades the operation of the dielectric resonator such as a cavity.

In 1983, S. Long was the first who showed that a dielectric resonator (DR) with low permittivity (8 < ε_r <20), placed in an open environment, has a low Q factor when it is excited by their lower modes [2]. This discovery has opened the prospect of a new type of antennas called 'dielectric resonator antennas, DRA' where the radiating element consists of a dielectric resonator. Since then, several DR antennas have been proposed and fabricated taking different shapes such as cylindrical, spherical, rectangular, ring or triangular forms [3- 6]. These studies have helped to highlight the many benefits of DR as radiating element, comparing with microstrip antenna, including: small size, high radiation efficiency, light weight, and absence of ohmic losses.

In recent years, several investigations have been reported to miniaturize the antenna structures to achieve wireless communications systems as compactly as possible. The

miniaturization and the integration of the radiating element in a system requires to be found by the designer. This compromise is required by the minimum dimensions of the antenna that is desired and its performances in terms of gain, radiation pattern, or shape. Several techniques are used for the ministration of the microwave circuits and devices such as;

defect the ground plane [7], perform short-circuits [8], insert micro/electronic components (capacitive or inductive elements) [9] and the use of novel materials (magnetic or electric material) with high permittivity [10, 11].

In the literatures, few research investigations are reported for the miniaturization of the resonator dielectric antennas. In this communication, we propose a reduced size rectangular dielectric resonator (RDR) antenna by stacking a ceramic BST film on the resonator element fabricated from the TMM10i.

This paper is organized as follows; the geometry and design theory of the antenna are described in the next section. In Section III, the results of simulation are presented and discussed. Finally, a conclusion is given in Section IV.

II. ANTENNA DESIGN AND THEORY

Figure 1 shows the configuration of the proposed structure.

The antenna is composed of two stacked dielectric resonators;

the first resonator is fabricated from the TMM10i dielectric material with permittivity ε_r1 = 9.8 and height of D1. The upper element consists of a thick film of BST ceramic (Ba0.8Sr0.2TiO3 material in paraelectric phase) with thickness of D2 and very high permittivity in the microwaves spectrum (εr2 = 250)[12]. The whole structure is mounted on a TMM6 substrate with constant dielectric of ε_rs = 6 and thickness h.

The ground plane is printed on the lower surface of the dielectric substrate. The radiated elements are excited via a microstrip transmission line. This alimentation technique allows exciting the Transverse Electric (TE_mnp) modes of the rectangular DRA, where the lowest order mode is TE₁₁₁ [13].

According to [13], the resonant frequency of the dominant mode can be determined theoretically using the dielectric waveguide model (DWM), by solving the following equation:

2 2

) 0

1 ( ) 2 /

tan( _{z r z}

z k d k k

k     (1)

where:

2 0 2 2

2 k k k

k_x  _y  _z _r

and

0

0 2 f

k   , k_xm/a, k_y n/b.

f₀ is the free operated frequency and the subscripts m, n, and p represent the field variation in the x-, y-, and z-directions, respectively.

(a) (b) Fig. 1. The antenna design (a) Top view (b) Side view.

The optimal parameters of the proposed antenna are recapitulated in the Tab.1.

TABLE I.OPTIMAL ANTENNA DESIGN PARAMETERS

Parameters Values (mm)

Parameters Values (mm)

L 25 W_f 4

W 25 D1 3.2

a 6. 5 D2 0.3

b 7 h 0.762

L_f 14.25

III. NUMERICAL RESULTS AND DISCUSSION

The electromagnetic characteristics simulations are performed by using two commercial software; the Computer Simulation Technology 'CST' Microwave Studio which utilizes the Finite Integration Technique (FIT) in time domain and the Ansoft High Frequency Structure Simulator (HFSS) based Finite Element Method (FEM) in frequency domain.

The first studied design consists of the same structure described in Fig.1 with a homogeneous dielectric resonator of TMM10i ceramic with a height of D=D1+D2=3.5 mm. Its reflection coefficient is presented at the Figure 2. It can be seen that the initial antenna design operates around 10.7 GHz with an impedance bandwidth between 10.2 GHz and 11.2 GHz, with reflection coefficients S₁₁ bellow than -10 dB.

6 8 10 12 14

-20 -15 -10 -5 0

Reflection Coefficient (dB)

Frequency (GHz)

Fig. 2. Reflection coefficient of the antenna with a homogeneous dielectric resonator.

In order to miniaturize the DR antenna, a thick film of BST ceramic with very high permittivity (ε_r2 = 250) has been loaded with the TMM10i material, as shown in Fig. 1. The reflection coefficients of the antenna before and after loading the BST material are illustrated in Fig. 3. From these curves, it can be observed that the integration of the BST layer leads to shift the resonant frequency from 10.7 GHz to 8 GHz.

6 7 8 9 10 11 12

-40 -30 -20 -10 0

Reflection Coefficient (dB)

Frequency (GHz) Simple DRA

DRA with Stacked BST

Fig. 3. Reflection coefficient of the antenna with and without loading the BST layer.

To measure the reduction rate of the antenna size, a new antenna is designed to resonate at the same frequency of the proposed antenna i.e. 8 GHz, as demonstrated at the Fig.4.

6 7 8 9 10 11 12

-20 -15 -10 -5 0

Reflection Coefficient (dB)

Frequency (GHz)

Fig. 4. Reflection coefficient of the rectangular dielectric resonator antenna with a size of 12×11.5 mm².

After the optimization of this antenna performance, it is found that the structure must take the following parameters:

for the dielectric resonator; a= 12mm, b = 11.5mm, and for the substrate; L=40mm, W=40mm. In the purpose to compare the two antenna size which operate at 8GHz, two rectangular are drawn in Fig. 5, where the rectangular with dark color represents the DRA with the loading BST material layer and the light one represents the simple DRA with TMM10i material. From this figure, it can be concluded that the miniaturization technique, adopted in this work, achieves a size reduction of the radiating element of 67%.

Fig. 5. Comparison of the antenna size operating at 8 GHz.

(a)

(b)

Fig. 6. The antenna design (a) Top view (b) Bottom view.

In addition, the radiation patterns (for the two principal planes E and H), depicted in Fig., show that the two antenna

have almost the same radiation behavior and that the miniaturized antenna provides a high gain (6.5 dB) compared with the simple DRA (4.3 dB).

6 7 8 9 10 11 12

-40 -30 -20 -10 0

Reflection Coefficient (dB)

Frequency (GHz)

HFSS Simulation CST Simulation

Fig. 7. The antenna design (a) Top view (b) Bottom view.

(a)

(b)

Fig. 8. The antenna design (a) Top view (b) Bottom view.

It is noted that all previous results are issued from the simulation using the CST MS software. To validate the obtained numerical results, the same miniaturized antenna structure, described in Fig. 1, was simulated by the Ansoft HFSS simulator. The antenna characteristics are compared and presented in terms of reflection coefficients and radiation patterns as presented in Fig. 7 and Fig. 8, respectively. The

main antenna performances for the two simulation tools are summarized in the Tab.2. From these figures (Figs. 7 and 8) and table (Tab. 2), it can be concluded that the simulated results obtained from the two simulators show a very good agreement.

TABLE 2.COMPARISON OF HFSS AND CSTSIMULATIONS

Resonant frequency

Impedance bandwidth

Realized Gain CST Simulation 7.99 GHz 32 MHz 6 dB HFSS Simulation 8.01 GHz 28 MHz 5.6 dB

To Study the effect of the BST ceramic thickness on the antenna performances, a parametric study is done by acting the value of this thickness D2, as illustrated in Fig. 9.

6 7 8 9 10 11 12

-40 -30 -20 -10 0

Reflection Coefficients (dB)

Frequency (GHz)

D2=0.2mm D2=0.3mm D2=0.4mm D2=0.5mm D2=0.6mm

Fig. 9. The antenna design (a) Top view (b) Bottom view.

IV. CONCLUSION

A Miniaturized dielectric resonator antenna with rectangular shape is presented, and numerically investigated.

The miniaturization technique adopted in this work consists of the utilization of stacked resonators with low/high permittivity (TMM10i/BST materials). The electromagnetic analysis are carried out by two commercial software; CST MS and Ansoft HFSS. The numerical results are presented in terms of reflection coefficients, radiation patterns and realized gains.

The obtained results show very good agreements. With this

characteristics, the proposed antenna structure has a compact size and can be suitable Radar applications.

References

[1] D. Kajfez and P. Guillon, Dielectric Resonators. Norwood, Artech, 1986.

[2] S. A. Long, M. W. McAllister, and L. C. Shen, ‘The resonant Cylindrical Dielectric Cavity Antenna,’ IEEE Transactions on Antennas and Propagation, vol. 31, pp. 406-412, 1983.

[3] M. W. McAllister and S. A. Long, ‘Resonant Hemispherical Dielectric Antenna,’ Electronics Letters, vol. 20, pp. 657-659, 1984.

[4] A. Ittipiboon, R. K. Mongia, Y. M. M. Antar, P. Bhartia, and M.

CUHACI, ‘Aperture Fed Rectangular and Triangular Dielectric Resonators for Use as Magnetic Dipole Antennas,’ Electronics Letters, vol. 29, pp. 2001-2002, 1993.

[5] R. K. Mongia, A. Ittipiboon, P. Bhartia, and M. Cuhaci, ‘Electric- Monopole Antenna Using a Dielectric Ring Resonator,’ Electronics Letters, Vol. 29, pp. 1530-1531, 1993.

[6] K. W. Leung, K. Y. Chow, K. M. LUK, and E. K. N. Yung, ‘Low- Profile Circular Disk DR Antenna of Very High Permittivity excited by a microstripline,’ Electronics Letters, vol. 33, pp. 1004-1005, 1997.

[7] G. Kossiavas, A. Papiernik, 'The C-Patch: A Small Microstrip Element,' IEE Electronics Letters, Vol. 25, pp. 253-254, 1989.

[8] K. Hirisawa, M. Haneishi, 'Analysis, Design and Measurement of small and Low-Profile Antennas,' Ed. Artech House, Chapter 5, 2002.

[9] P. Ciais, R. Staraj, G. Kossiavas, C. Luxey, 'Design of an Internal Quad- Band Antenna for Mobile Phones,' IEEE Microwave and Wireless Components Letters, Vol. 14, pp. 148-150, 2004.

[10] R.C. Hansen, M. Burke, 'Antennas with magneto-dielectrics,' Microwave and Optical Technology Letters, Vol. 26, pp. 75-78, 2000.

[11] S.A. Tretyakov, M. Ermutlu, 'Modeling of Patch Antennas Partially Loaded with Dispersive Backward-Wave Materials', IEEE Antennas and Wireless Propagation Letters, Vol. 4,2005, pp. 206-269.

[12] F.H.Wee and F.Malek, 'Gain Enhancement of a Microstrip Patch Antenna using Array Rectangular Barium Strontium Titanate(BST), ' The 2011 Loughborough Antennas and Propagation Conference, November 14-15, 2011, Loughborough, UK.

[13] I. Messaoudene, A. Benghalia, M. A. Boughendjour, and B. Adjaoud 'Numerical investigations of ultra wide-band stacked rectangular DRA excited by rectangular patch,' Prog. Electromagn. Res. C (PIER C), Vol.

45, pp. 237–249, 2013.