A Novel Metamatarial SRR for WaveguideAntenna

Mahd i Jalali

Departm ent of Electr ical Engineering, IAUUrmia, Iran

Jalal i.mahdiiWgmail.com

Tohid Sedghi

Department of Electrical Engineering,Urmia, Iran

st t.sedghiiWurmia.ac. ir

Majid Shokri

Department of Electr ical Engineer ing,Urmia, Iran

Maj id.shokr i2944iWgmail.com

Abstract- In this paper, an open - ended rectangularwaveguide antenna loaded with three type ofSRRs, radiatingbelow the cut-off frequency of the waveguide are desigendand a novel metamaterial SRR, Triangular Split RingResonators and Wire Strip (TSRR-WS), is proposed. Thiswork has investigated design development, simulation,miniaturization and are comparing with these four types ofSRRs of an open end a waveguide dual band antenna. A noveltechnique was employed to miniaturize the open-endedradiator using electromagnetic metamaterials (MTM). Theantenna is capable of radiating below the cutoff frequency ofthe waveguide by supporting backward waves. Comparingprevious work of miniaturization of waveguides, a betterbandwidth about 600 MHz, good matching, dual band andlow profile (with 5 unit cell ofMTMs) antenna is obtained.

Index Terms- dual band antenna ,metamaterials,waveguide.

I. INTRODUCTION

In the last few years, there have been several new ideaswhich may to the miniaturization of waveguides [1].Recently, a very unusual waveguide was proposed byMarques et al. in [2] and then extensively studied byHrabar et al. in [3]. Marques et al. proposed a rectangularmetallic waveguide periodically loaded with resonantmagnetic scatterers, so-called split - ring resonators(SRR's) [3]-[6], [9], [10]. The design of split rings is veryimportant to construct a new type of MTMs. Numeroustypes of different ring and ring-like structures such ascircular, square, Q-shaped, V-shaped, S-shaped and othersare used to create new MTMs [7]. In the light of the knownstructures we decided to use a new MTM which consist ofa triangular shaped ring which has been proposed in[8]. Weuse this structure in an open ended waveguide antenna anddo simulation in the frequency range of 5-9 GHz.Simulation results are presented below. This kind of

Manuscript received May 10,2009. This work was supported in part bythe IslamicAzad university of Urmia branch.

M. Jalali is with the Islamic Azad University of Urmia branch, Iran(phone: 098-914-389-9112); e-mail: JalaILmahdi@gmail.com).

T. Sedghi was with the Islamic Azad University of Urmia branch, Iran.He is now with the Department of electrical engineering, Urmia University,Iran (e-mail: stJ sedghi@urmia.ac.ir).

Y. Zehforoosh is with the Electrical Engineering Department, IslamicAzad university of Urmia, Iran, (e-mail: y.zehforoosh@srbiau.ac.ir).

resonator has negative permittivity and permeability in theused frequency band. An X-band, open ended waveguideantenna loaded with five unit cells TSRR-WS, which isradiating below the cutoff frequency with a goodbandwidth and better impedance matching, is designed andsimulated.

II.THEORETICAL ANALYSIS AND SIMULATION

In the simulations first we use combination of SRR1 andWS2 structures to fabricate artificial MTM. Figure 1illustrates the geometry of the unit cell comprised ofTSRRand WS.

Figure 1. Unit cell of new metarnaterial

A FR4 sheet of 0.25 mm thickness (with relativepermittivity 4.4) is used as substrate for each configuration.TSRR and WS are made of copper with conductivity of5.8x107 S/m. the width ofall TSRRs is 0.4 mm. TSRRs arelocated on one face of FR4 and WSs are etched on theiropposite face. We use Ansoft's High Frequency StructureSimulator (HFSS) software; based on finite-elementmethod (FEM).The width of WS is chosen 0.5 mm. Thebase and height of TSRR are 7.794 and 6.75 mmrespectively. The gap in each TSRR is O.3mm and spacebetween TSRRs is O.4mm [8].Left handed medium is simulated by a regular array of fiveTSRR-WS placed in the symmetry plane of60mm long. Ina lossless case, the longitudinal propagation factor of thiswaveguide is given by the simple set of equations [4]:

1 Split Ring Resonator2 Wire Strip

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_+ [(!c)2] _ !co _mekz -_ko e.u; 1- - .t. - ~'!co-- m=I,2,3,···f +-.j&rJ.1/r 2a

Here, k z stands for waveguide propagation factor, kg isa free space propagation factor, e; is relative permittivityand Jitr and /lir stand for relative permeability intransversal(x) and longitudinal (z) directions of thewaveguide, respectively. The symbol f stands for

frequency of the signal, whereas fCD and fc are thecut-off frequency of an empty waveguide and thewaveguide filled with a material respectively. The X-bandwaveguide loaded with TSRR-WS is excited by a C-bandwaveguide-to-coaxial transition (cutoff frequency 4.3GHz). To ensure the excitation ofthe first SRR in the array,the first ring was partially placed out from the X-bandwaveguide; and to improve the radiation, the last ring waspartially placed out from the open end of the waveguidealong with an extra ring as shown in figure 2.

Figure 2. Schematic of the waveguide antenna with 5 unit cell ofMTMs

Obtaining passband below the cutoff frequency of thewaveguide is not proof of a backward wave. In figure 4,which shows the phase and magnitude of the guided wave,it is clearly seen that in the passband, the phase of the waveincreases unlike as in an ordinary waveguides where phasedecreases. Thus, physically longer waveguides exhibitlarger phase of SII' This is because the direction of thephase velocity is opposite to the energy flow. This provesthat there is a phase advance in such waveguides unlikephase delay in an ordinary waveguide. With this, one canconclude, physically longer backward wave waveguideappears electrically shorter with phase advance (figure 4).

4.00

2.00

e- 0.00>-

-4.00~?;;-~~~....,....;----~~-----;-=-~~~....,.... ,.........-~~---;;-;,5. 0 7. 0

Freq[GHz]

Figure 4. Phase (solid) and magnitude (dotted) of Sj, for antennawith 5 unit cells

In the figure 5 and 6 E-plane and H-plane patterns of theantenna in resonance frequencies are depicted. Thepatterns show that the antenna works like an ominidirectional antenna on resonance frequencies.

o

Reflection coefficient SII at the input port for antenna isplotted in figure 3. From the plot, one can notice that thepropagation passband is located well below the cut offrequency of X-band waveguide with the bandwidth 600MHz. Minimum return loss computed is 18 dB. Comparingthis to previous works of miniaturization of waveguides in[2], [3], a larger bandwidth obtained with low profile andthe less number ofcells.

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..in;? -e

"-10

-12

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-185 5.5 6.5 7 7.5

Frequency[GHz)8.5 9

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1

.90 1----'---I- -+-- - ----';jIlE'---- - -+------if----------,·, 90

•J.JJ

J,.120

·150

·180

Figure 5. E-plane (solid) and H-plane (dotted) of antenna with 5unit cells in 5.48GHz

Figure 3. Return loss plot for Antenna with 5 unit cells

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o

-901-_-7_1-"7"'~~~__-J-j -j

B. Analysis ofwaveguide antenna for different dielectricsubstrate

To see the effect of using different dielectric substrates inthe waveguide antenna structure we use a Rogers RT/duroid5870 with relative permittivity of 4.4 and dielectric losstangent of 0.0012. Simulation results are presented in figure8. As it is obvious using a substrate with lower relativepermittivity cause a shift in bandwidth frequency range forlower band and a smaller bandwidth for higher band . Sochoosing FR4 as a proper dielectric substrate to have a lagerbandwidth and less return loss is suitable .

-150 150

-180

Figure 6. E-plane (solid) and H-plane (dotted) of antenna with 5unit cells in 7.8GHz

--FR4epoxy- ,_ .•Roger1s RTduroid5870

A. Analysis ofwaveguide antenna for different number ofcells

8.5

8.5

i/

II

IiI

. 1I~

\'\\ / I

III

7.5

6.5 7 7.5

FreqJellt)'{GHzj

7FrequenCYIGHz)

6.5

5.5

5.5

·J55~-___::'::_---"---~--_':__--__:'_:----l.-----I-=-----J

-5

-15

-10

-20 '--__-"-__--'--__--'-__---1 -'-__--'-__--'-__---'

5

Figure 9. Return loss plot for Antenna with different Substrates

51

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'5r-'. C"y_' ,I f

.for\ iI J

I'- ,I<ll \'

~ .15 \:- "" """

r.3Q-

Figure 8. Return loss plot for Antenna with different substrates

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I,j

I ;i ii ii ii i\ijiiiiiYii;

III. PARAMETRIC ANALYSIS i5'::.

There are lots of parameters that affect on the antenna Vi

characteristics such as return loss and bandwidth. To see theeffect of the parameters, there are some parametric analysesbelow.

For analysis of the antenna characteristics for differentnumber of cells we use 3, 4,5 and 6 cells in the antenna anddo simulat ion. The SII is presented in figure 7. results showsthat the bandwidth is fully depend on the number of cellsused in the antenna. Also it is obvious that a larger bandwidth with the respect of cut-off frequency of the waveguideis obtained when we use 5 cells in the antenna .

-25

o

-40

·5

-35

-10

-15

-30

~ -20

"

98.56.5 7 7 .5Frequency[GHZ]

65.5.45 5~-----='::----:------=:'::---=------=:'::----=---::'::----:

Figure 7. Return loss plot for Antenna with different number ofcells

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IV. CONCLUSION

Simulation of TSRR-WS loaded X-band waveguideantenna radiating below the cutoff frequency wassuccessfully carried out. According to simulations, theantenna operated about 5 GHz, 1 GHz below the cut offfrequency ofthe waveguide. The antenna had a bandwidth of600 MHz. The primary goal of the research was tominiaturize a waveguide antenna using novelelectromagnetic metamaterial rather than classical dielectricinclusion. The radiation property of the antenna does notdepend on the cross section of the waveguide, but on theinclusion. Transverse width of such a waveguide can be, inprinciple, arbitrarily small. The lowest frequency ofradiation, and therefore the miniaturization, is dictated byfeasibility of fabrication of the metamaterial at the frequencyof interest. We design a smaller, compact, and low profileantenna with better bandwidth from before works.

ACKNOWLEDGMENT

The authors would like to thank Islamic Azad universityofurmia branch for it's support.

REFERENCES

[1] Waveguide handbook, Nathan Marcuvitz, 1986, lET.[2] R. Marques, J. Martel, F. Mesa, and F. Medina, "Left-handed-mediasimulation and transmission of EM waves in subwavelengthsplit-ring-resonator-loaded metallic waveguides," Phys. Rev. Lett., pp.183 901-183 904, Oct. 2002.[3] Silvia Harbar, Juraj Bartolic, Zvonimir Sipus, "WaveguideMiniaturization Using Uniaxial Negative Permeability Metamaterial",IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION,VOL. 53, NO.1, JANUARY 2005.[4] X.-C. Zhang,Z.-Y. YU,and J. Xu, "Novel band -pass substrate

intenerated waveguide (SIW) filter based on complementary split ringresonators(CSRRS)" Progress In Electromagnetics Research, PIER 72,39-46,2007[5] J.-X. Niu, X.-L. Zhou, andL.-S. Wu, "Analysis and application ofnovel structures based on split ring resonators structures based band onsplit ring resonators and coupled lines" Progress In ElectromagneticsResearch, PIER 75, 153-162,2007[6] S. Xi, H. Chen, B.-I. Wu and 1. A. Kong, "Experimental confirmationof guidance properties using planar anisotropic left-handed metamaterialsslabs based on s-ring resonators," Progress In Electromagnetics Research,PIER 84, 279-287, 2008

[7] J. B. Pendry, A. J. Holden, D. J. Robbins, and W. J. Stewart,"Magnetism from conductors and enhanced nonlinear phenomena," IEEETrans. Microwave Theory Tech., vol. 47, p. 2075, 1999.[8] C.Sabah and S.Uckun"Traingular Spit Ring Resonator and Wire Stripto From New Metamatrial" URSI General Assembly Proceeding pp. 216­220, August 2008.[9] D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, and S.

Schultz, "A composite medium with simultaneously negativepermeability and permittivity," Phys. Rev. Lett., vol. 84, no. 18, pp.4184-4187, May 2000.[10] C. Caloz, A. Sanada, and T. Itoh, "Microwave circuits based onnegative refractive index material structures," in Proc. EuMc2003,Munich, 2003, pp. 389-392. X.-L. Zhou and L.-S. Wu, "Analysisand application of novel structures based on split ring resonatorsstructures based band on split ring resonators and coupled lines" ProgressIn Electromagnetic Research, PIER 75, 153-162,2007.

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