Wideband Circularly Polarized Conical Dielectric Resonator Antenna

Raggad Hedi Groupe Radio & Hyperfréquences

ESEO, 4 Rue Merlet de la Boulaye, BP 30926, 49009 Angers, France

hedi.raggad@eseo.fr

Latrach Mohamed

Groupe Radio & Hyperfréquences ESEO, 4 Rue Merlet de la Boulaye, BP 30926, 49009

Angers, France mohamed.latrach@eseo.fr

Razban Tchanguiz IREENA, Ecole polytechnique de l’Université de Nantes,

BP 50609, 44306 Nantes, France

tchanguiz.razban@univ-nantes.fr]

Gharsallah Ali

Circuits et Systèmes Electroniques Hautes Fréquences, Université de

Tunis EL MANAR, Tunisie ali.gharsallah@gmail.com

Abstract— A wideband circularly polarized (CP) conical dielectric resonator antennas (DRA) is investigated in this paper. The DRA is excited by a single 45 inclined slot fed by a microstrip feed line. The inclination of the slot creates a circular polarization of the radiated wave. The gain of the dielectric resonator antenna varies between 4.8 and 7.2 dBi. This study analyze also à parametric study on the effect size of dielectric resonator on bandwidth and coefficient of reflection. The reflection coefficient, AR, radiation pattern, and antenna gain of are studied, and reasonable agreement between the measured and simulated results is observed

Keywords-component; Conical DRA; Wideband; circularly polarized.

I. INTRODUCTION (HEADING 1) Dielectric resonator antenna (DRA) is actually derived from the dielectric resonator (DR) [1], which was previously used for miniaturization of the active and passive microwave circuits such as the filters and oscillators. DRs of different shapes have various modes of oscillation. With the proper excitation of certain modes and with no shielding, these resonators can actually become efficient radiators instead of energy storage devices. This concept led to the exploration of the DRs as antennas [2]. The DRA has various advantages such as the compact size, light weight, high radiation efficiency, ease of excitation, high power handling capability, and wideband capability. Depending on the resonator shape and feeding methods, various modes can be excited within the DRA radiating element. These modes can produce different radiation patterns for various coverage requirements [2-3], Recently, however, substantial research efforts have been put on the circularly polarized (CP) DRA [4]–[5] because the CP system allows a more flexible orientation between the transmitting and receiving antennas.

It was believed that the bandwidth of the dielectric resonator antenna would be small because of the high dielectric quality factor. Several techniques have been proposed to further increase the bandwidth of the dielectric resonator antennas. Such as stacking two dielectric resonators on top of each other can increase the bandwidth up to 25% [6]. introducing an air gap between the DRA and ground plane [7], and merging two or more DRA modes [8], [9]. These methods were originally demonstrated for LP DRAs, but can be extended to CP DRAs. For example, a CP rectangular notch DRA with an AR bandwidth of 5% was designed [10]. Also, a CP rectangular stair-shaped DRA with an AR bandwidth of 10.6% was presented [11]. In this letter, a wideband singly fed CP conical DRA is investigated for the first time. It is found that an AR bandwidth of as wide as 21.5% can be obtained by feeding the DRA with a simple inclined slot. The inclined slot excites orthogonal degenerate modes that produce circularly polarized fields. To the best of our knowledge, it is the widest AR bandwidth that can be obtained thus far from a singly fed DRA. It was found that multiple resonant modes with close resonance frequencies are excited and merged together, giving a very wide CP bandwidth.. In this letter, a notched conical DRA is also proposed to improve the impedance match.. The return losses, ARs, radiation patterns, and antenna gains of the original and modified configurations were simulated using HFSS V12. To verify the simulations, measurements were carried out. Reasonable agreement between the measured and simulated results was obtained.

II. ANTENNA RECONFIGURATION The geometry of the proposed antenna is shown in Figure 1. It includes a conical dielectric ARD εrd = 10, height h = 35 mm and radius respectively r1 = 9.5mm, r2 = 5 mm which is centered on a crack inclined at 45 ° Ls length 12mm, Ws = 1

mm. The antenna is mounted on a ground plane that is 60 * 60mm ² in size. The assembly is excited by a microstrip line of Wm = 2mm and Lm = 37mm printed on a FR4 substrate with a permittivity εrs = 4.4 and thickness t = 0.8 mm.

Figure 1. Antenna structure

III. RÉALISATION ET ÉTUDE EXPÉRIMENTALE The original conical DRA is studied first. Fig. 2 shows the measured and simulated of the reflection coefficients. With reference to the figure, reasonable agreement between the measured and simulated results is obtained, with the discrepancy caused by experimental tolerances. The measured and simulated 10-dB impedance band widths dB are 33.5% (2.88---4.04 GHz) and 28.1% (3.00---3.98 GHz), respectively, whereas the measured and simulated 3-dB AR bandwidths are 21.5% (3.11---3.86 GHz) and 22.6% (3.22---4.04 GHz), respectively. It should be mentioned that the entire measured AR passband falls within the impedance passband, which is highly desirable. Fig. 3 shows the antenna gain. It is noted from the figure that the measured gain varies between 5.28 and 8.40 dBi across the passband (3.11---3.86 GHz) and is maximum (8.40 dBi) at around 3.2 GHz. Fig. 4 shows the measured and simulated broadside radiation patterns at 3.3 and 3.6 GHz

3.5 4 4.5 5 5.5-35

-30

-25

-20

-15

-10

-5

0

Fréquence (GHz)

S11

(dB

)

mesure

simulation

Figure 2. Coefficient of reflection

Figure 3. radiation pattern

Figure 4. Gain 3D

IV. PARAMETRIC STUDY The geometry of the antenna is shown in Fig. 1. The conical DRA has a radius R1 ,R2 and a height h. The value of h was chosen as 35mm. The DRA is excited by a slot located at the Centre of the ground plane. The dielectric constant of the DRA is 10,. The impedance bandwidth, resonance frequency and radiation pattern are investigated to observe what effects of same dimension of structure has on these two important figures of merit for the DRA.

1). Height of dielectric resonator (h)

The height of dielectric resonator hasn't a vital effect on the antenna resonance frequencies. The effect of this parameter is shown in Fig.4.

3.5 4 4.5 5 5.5 6 6.5 7-40

-30

-20

-10

0

Frequency (GHz)

S11

(dB

)

h=40mm

h=35mmh=30

Figure 4. S11 vs. Hdr

2). Radius of dielectric resonator

The dielectric resonator is fed by a slot with the fundamental mode is excited. The diameter has more importance and effect to the resonance frequency. The rayon of the dielectric resonator is adjusted to improve the antenna matching and investigate its effect on antenna resonance and the effect of conical shapes to widen the bandwidth .

3.5 4 4.5 5 5.5 6 6.5 7-40

-30

-20

-10

0

Frequency (GHz)

S11

(dB

)

R2=5.5mm

R2=7.5mmr3=9.5mm

Figure 5. S11 vs. R2

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[8] G. Almpanis, C. Fumeaux, and R. Vahldieck, ‘‘The trapezoidal dielectric resonator antenna,’’ IEEE Trans. Antennas Propag., vol. 56, no. 9, pp. 2810---2816, Sep. 2008.

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[10] S. M. Deng and C. L. Tsai, ‘‘A broadband slot-coupled circularly polarized rectangular notch dielectric resonator antenna fed by a microstrip line,’’ in Proc. IEEE Antennas Propag. Soc. Int. Symp., 2005, vol. 4B, pp. 246---249.

[11] R. Chair, S. L. S. Yang, A. A. Kishk, K. F. Lee, and K. M. Luk, ‘‘Aperture fed wideband circularly polarized rectangular stair shaped dielectric resonator antenna,’’ IEEE Trans. Antennas Propag., vol. 54, no. 4, pp. 1350---1352, Apr. 2006.