Dual band patch antenna based on Complementary Rectangular Split-Ring Resonators

N. Ortiz, F. Falcone, M. Sorolla

Millimeter Wave Laboratory, Public University of Navarra Campus Arrosadía, E-31006 Pamplona, Spain

ortiz.25739@e.unavarra.es francisco.falcone@unavarra.es

mario@unavarra.es

Abstract — A simple and successful dual band patch

rectangular antenna design is presented. The dual band antenna is designed etching a complementary rectangular split ring resonator in the patch of a conventional rectangular patch antenna, achieving a miniaturization of the conventional antenna. The dual band antenna design has been made feasible due to the quasi-static resonance property of the complementary split ring resonators. Simulated results are compared with measured data and good agreement is reported.

Index Terms — Dual Band Patch antenna, Complementary Split Ring Resonator, Metamaterials.

I. INTRODUCTION

The possibility of obtaining media with simultaneously negative permeability and permittivity was hypothesized by Veselago in the late 1960s [1]. In spite of the interesting properties presented by such media, it was not until 2000 that the first experimental evidence of a medium with simultaneously negative permeability and permittivity was demonstrated [2]. The original medium proposed in [2] consists of a bulky combination of metal wires and split-ring resonators (SRRs) [3].

The SRR electromagnetic properties have been already analyzed in [4, 5]. This analysis shows that the SRR behaves as an LC resonant tank that can be excited by an external time-varying magnetic field applied parallel to the particle axis, thus producing a quasi-static resonant effect [4]. Therefore, the SRR has sub-wavelength dimensions at its quasi-static resonance, allowing very compact device designs.

When up to now, these self-resonant particles have been used in the design of microwave filters in planar technology [6, 7]. However, in this paper, we have taken advantage of complementary split-ring resonator (CSRR) concept [8] to design a dual band patch antenna. The CSRR is inspired on Babinet principle [9] and, as occurs with the SRR, it also exhibits a quasi-static resonance, which make the particle electrically small [8, 9].

The use of a CSRR etched in the patch of a conventional patch antenna allows us to design a dual band patch antenna. The first resonance of the dual band antenna is produced by the excitation of the CSRR in the patch, miniaturizing both patch antenna resonances.

Replacing a CSRR with an iris of its same external dimensions, the iris does not exhibit a resonance at the same

frequency of the CSRR. The resonance frequency of a rectangular iris on a dielectric is approximately given by clight

/ rba ε⋅+ )( , where c light, εr, a, and b are the speed of light in vacuum, dielectric relative permittivity and the external dimensions of the rectangular iris, respectively. In opposition to the resonance frequency of a rectangular iris, the resonant frequency of the CSRR is much lower for the same physical size. Hence, the lower frequency of the dual band antenna is easily designed by exciting the CSRR etched in the centre of the patch antenna.

(a)

(b)

Fig. 1. (a) SRR and CSRR topology and relevant design parameters. (b) Layout of the dual patch antenna with the centre of the CSRR etched at point A, (X= -9.3mm, Y= 15.54mm)

II. DUAL BAND ANTENNA DESIGN

Dual band patch antenna design must be split into two stages. The first stage is considered to be the design of a

978-1-4244-2802-1/09/$25.00 ©2009 IEEE 2762

conventional patch antenna [10], which resonates at higher frequencies of the desired higher frequency band for the dual band patch antenna. The second stage is the design of the CSRR particle (see Fig. 1) by choosing the values of its design parameters, a, b, c, d and s to resonate at lower desire frequency for the dual band antenna. Thus, the right excitation of the CSRR particle is needed for the dual antenna design. The excitation of CSRRs has been usually driven by an incident electric field normal to the particle plane. In order to understand the excitation of these particles, let us consider the CSRR presented in Fig 1(a). Following the theoretical discussion shown in [4], the operation of the SRR near its first resonance frequency obeys to the effect of resonant polarizabilities, which gives the resonant magnetic and electric dipolar moments mz, px and py as a function of the exciting field components inc

zB , incxE , and inc

yE .

Complementarily, using Babinet’s principle [9], the CSRR can be excited by the incident complementary fields,

inccE and inccB , which are related to incE and incB by incincc BcE ⋅= and incincc EcB ⋅−= )/1( by means of

another set of resonant polarizabilities, thus given an electric dipole c

zp and magnetic dipoles cxm and c

ym . Although the

CSRR can be excited by different field components, the orientation of the CSRR used in the prototype allows its proper excitation driven by the magnetic field component yB . Thus, the CSRR must be placed at the centre

zone (see Fig. 1 (b)) of the rectangular patch, where the magnetic field in the patch is maximum (see Fig. 1(b)).

This result opens the possibility to design dual patch antennas just etching a CSRR in its patch, without introducing any modification in the conventional patch of the antenna. Besides, the location of the CSRR in the centre part of the patch (see Fig.1 (b)), reduces the resonant frequency of the conventional patch, shifting the frequency of the conventional patch to lower frequencies, without increasing patch dimensions. The prototype has been simulated with the commercial finite-integration time-domain CST Microwave Studio code, see Fig. 3, Fig. 4 and Fig. 5.

III. EXPERIMENTAL RESULTS

To demonstrate the usefulness of the designed dual antenna, a prototype has been fabricated and measured. The substrate employed is the commercially available Arlon 250-LX-0193-43-11 (εr=2.43, thickness h=0.49mm). The first step is to fabricate a conventional rectangular patch antenna. The resonant frequency of the patch antenna has been set around 5GHz. The selected rectangular patch dimensions are: width of 18.43mm and length of 23.68mm [10]. The microstrip line which feeds the patch is W=1.34mm, corresponding to a characteristic impedance of 50Ω. The feed microstrip line presents an offset from antenna centre to achieve a good matching at its working frequency. The offset is (X1= -13.37mm, Y1=0mm).

The second step is to choice the CSRR particle for presenting its resonance frequency around 4.2GHz. The necessary physical dimensions to achieve this frequency has been calculated by using the design formulas for SRR reported in [4], resulting in this case a=4.6mm, b=4.2mm, c=d=0.2mm and its coordinates from its centre to the origin

are marked by point A (See Fig. 1(b)), being the coordinates of this point (X=-9.3mm, Y=15.54mm). The dual antenna prototype has been designed to exhibit a dual behaviour in two frequency bands presented in the range from 4GHz to 5GHz for WLAN applications. The prototype has been fabricated using a laser drilling machine. A photograph of the prototype is shown if Fig. 2.

Fig. 2. Photograph of the fabricated prototype.

In Fig.3 simulated and measured reflection coefficient results are shown. For matching measurements data has been collected by using a HP8510 network analyzer.

Fig. 3. Simulated and measured reflection coefficient results.

As it can be seen in Fig. 3, there is a frequency shift of

246MHz for the lower resonance frequency, being the measurements results shifted to lower frequencies. The upper resonance presents a frequency shift of 84MHz to lower frequencies. Although there is a frequency shift between simulated and measured results, the matching values achieved are properly predicted by simulations. The discrepancies between simulated and measured results are due to manufacturing process. In simulations materials have been simulated considering its corresponding finite conductance and substrate has been simulated considering dielectric losses. In Fig. 4(a) and Fig. 4(b) simulated and measured directivity radiation pattern results are shown for 0º, 45º and 90º phi cut planes for the first resonant frequency. Meanwhile, Fig. 5(a) and Fig. 5(b) show simulated and measured directivity

CSRR

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radiation pattern results for 0º, 45º and 90º phi cut planes for the second resonant frequency.

Directivity patterns have been obtained from measured gain and efficiency values in order to show the feasibility of dual band antenna based on CSRR’s, as depending on CSRR dimensions and its location inside the patch efficiencies up to 50% for each frequency band can be obtained.

(a)

(b)

Fig. 4 (a) Simulated (F1=4.436GHz) and (b) Measured (F1=4.19GHz) directivity radiation pattern results for Phi=0º, 45º and 90º phi cuts for the first frequency band.

(a)

(b)

Fig. 5. (a) Simulated (F2=4.892GHz) and (b) Measured (F2=4.808GHz) directivity radiation pattern results for Phi=0º, 45º and 90º phi cuts for the second frequency band.

Table1 shows a comparison between simulated and measured results from matching and radiation point of views. From matching point of view, the main characteristics shown in Table1 are reflection coefficient values and effective bandwidth. For radiation point of view the main parameters shown in Table1 are peak directivity, peak gain and radiation efficiency. As it can be seen in Table1 a good agreement between simulated and measured results are shown.

IV. CONCLUSIONS

A dual band patch antenna based on CSRRs has been proposed and successfully tested. A good agreement between simulated and measured results is shown. The design of the dual band patch antenna is very easy, as the only design parameters comparing to a conventional patch antenna are the ones of the CSRR particle design parameters. Besides, thanks to the presence of the CSRR a miniaturization of the patch is achieved.

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REFERENCES

[1] V. G. Veselago, “The Electrodynamics of Substances with Simultaneously Negative Values of ε and μ”, Soviet Physics Uspekhi, Vol. 10, No. 4, pp. 509 - 514, January – February 1968.

[2] D.R. Smith, W.J. Padilla, D.C. Vier, S.C. Nemat-Nasser and S. Schultz, “Composite medium with simultaneously negative permeability and permittivity”, Phys. Rev. Lett., Vol. 84, pp. 4184-4187, May 2000.

[3] J. B. Pendry, A. J. Holden, D. J. Robbins, and W. J. Stewart, “Magnetism from conductors and enhanced nonlinear phenomena,” IEEE Trans. Microwave Theory Tech., Vol. 47, p. 2075, 1999.

[4] R. Marqués, F. Mesa, J. Martel and F. Medina, “Comparative analysis of edge and broadside coupled split ring resonators for metamaterial design. Theory and Experiment”, IEEE Trans. Antennas and Propagation, Vol. 51, pp. 2572-2581, October 2003.

[5] R. Marqués, F. Medina, and R. Rafii-El-Idrissi, “Role of bianisotropy in negative permeability and left handed metamaterials,” Phys. Rev. B, Condens. Matter, vol. 65, pp. 144 441(1)–144 441(6), 2002.

[6] F. Martín, F. Falcone, J. Bonache, T. Lopetegi, R. Marqués, and M. Sorolla, “Miniaturized coplanar waveguide stopband filters based on multiple tuned split ring resonators,’’ IEEE Microw. Wireless Compon. Lett., Vol. 13, no. 12, pp. 511---513, Dec. 2003.

[7] F. Falcone, F. Martín, J. Bonache, R. Marqués, T. Lopetegi, and M. Sorolla, “Left handed coplanar waveguide band pass filters based on bi-layer split ring resonators,’’ IEEE Microw. Wireless Compon. Lett., Vol. 14, no. 1, pp. 10---12, Jan. 2004.

[8] F. Falcone, T. Lopetegi, J.D. Baena, R. Marqués, F. Martín and M. Sorolla, “Effective negative-ε stop-band microstrip lines based on complementary split ring resonators”, IEEE Microwave and Wireless Components Letters, Vol. 14, No. 6, pp. 280-282, June 2004.

[9] F. Falcone, T. Lopetegi, M.A.G. Laso, J.D. Baena, J. Bonache, M. Beruete, R. Marqués, F. Martín and M. Sorolla, “Babinet principle applied to metasurface and metamaterial design,” Phys. Rev. Lett., Vol. 93, pp. 397-401-1-4, 2004.

[10] J. D. Kraus, R. J. Marhefka, Antennas for all applications, Third Edition, McGraw-Hill, New York, 2002

TABLE I

Parameters Simulated Results

Measured Results

Matching Characteristics First Resonance (F1)

F1, (GHz) 4.436 4.19 Reflection coefficient, (dB) -16.94 -21.25

Ef_BW@-5dB (%) 1.53 1.52 Ef_BW@-10dB (%) 0.76 0.72

Second Resonance (F2) F2, (GHz) 4.892 4.808

Reflection coefficient, (dB) -16.98 -13.86 Ef_BW@-5dB (%) 1.67 1.72

Ef_BW@-10dB (%) 0.83 0.78 Radiation Characteristics

First Resonance (F1) Peak Directivity, (dBi) 7.142 7.36

Peak Gain, (dB) -0.083 -0.11 Radiation Efficiency (%) 19.27 17.92

Second Resonance (F2) Peak Directivity, (dBi) 7.298 7.74

Peak Gain, (dB) 5.984 5.85 Radiation Efficiency, (%) 73.89 64.83

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