Garg et al

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Research Journal of Physical and Applied Science Vol. 1(1), pp. 013 - 019, August 2012 Available online at http://www.wudpeckerresearchjournals.org2012 Wudpecker Research Journals

Full Length Research Paper

Analysis and design of microstrip patch antenna loadedwith innovative metamaterial structure

Bimal Garg, Ankit Samadhiya, Rahul Dev Verma

Department of Electronics Engineering, Madhav Institute of Technology and Science, Gwalior, India

Accepted 20 June 2012

In this work the values of permeability and permittivity of proposed innovative metamaterial structure,which is composed of “Array of rectangular rings with rectangular strips”, are obtained by using afictitious rectangular waveguide having perfect electric conductor and perfect magnetic conductor

walls. For verifying that the proposed metamaterial structure possesses negative values of Permeabilityand Permittivity within the operating frequency range, Nicolson-Ross-Weir method (NRW) has beenemployed. The patch antenna along with the proposed metamaterial structure is designed to resonateat 1.47GHz. Simulation results showed that the impedance bandwidth of the RMPA is improved by22.3MHz and return loss is reduced by 15.33dB by inco rporating the proposed metamaterial struc ture.For simulation purpose CST-MWS software has been used.

Key words: Impedance bandwidth, Nicolson-Ross-Weir (NRW) Rectangular Microstrip Patch Antenna (RMPA),Return loss.

INTRODUCTION

Microstrip Patch Antennas are designed on a dielectricsubstrate, which is composed of aradiating patch on oneside and ground plane on the other side as shown inFigure 1. These are low profile, lightweight, low costantennas. In spite of having a lot of advantages theseantennas have some drawbacks like narrow-bandwidth,

low gain, high return loss etc. (Gupta and Dhaliwal 2011).

To overcome Patch Antenna’s drawbacksseveralresearches have been done on patch antennas. In thisarea of research,Victor Veselago (1968) Engheta andZiolkowski (2006) introduced the theoretical concept of metamaterials. According to the theory of Veselago, theseare generally artificial materials used to provide

properties, which are not found in readily availablematerials in nature Pendry (2000) Garg et al., (2011). For improving the performance of patch antennas (Pendry etal., (1999) added more information. They proved that thearray of metallic wires can be used to obtain negativepermittivity and split ring resonators for negativepermeability. On the basis of this information,

*Corresponding author E-mail:[email protected].

Smith et al. (2001) fabricated a structure which was acomposition of split ring resonator and thin wire. It hadbeen observed that the structure proposed by thempossessed the negative values of permittivity andpermeability simultaneously and was named as LHM (Wuet al., 2005) Burokur et al., 2005).

In this work “Array of rectangular rings with rectangulastrips” as a metamaterial structure has been introducedfor reducing the return loss and ameliorating thebandwidthand directivity of the RMPA. Metamateriasubstrate size variation may affect the antennaparameters and to see its effect on proposed antennaparameters, variations in metamaterial substrate have

been done. Along with these outcomes, it has been observed thathis structure satisfies the double negative property withinthe operating frequency range.

ANTENNA DESIGNING PROCEDURE ANDSIMULATION RESULTS OF RMPA WITH andWITHOUT METAMATERIAL STRUCTURE

The RMPA parameters are calculated from the formulae

given below.



Figure 1. Microstrip Patch antenna.

Desired parametric analysis (Balanis, 1997;Stutzmanand Thiele, 1998)

Calculation of Width (W)

= = ……….. (1)

Where;c = free space velocity of lightεr = Dielectric constant of substrate

Theeffective dielectric constant of the rectangular microstrippatch antenna.

= + …………...(2)

The actual length of the Patch (L)

L =Leff - 2ΔL ………………………………… (3)

Where

Leff= …………………………… (4)

Calculation of Length Extension

∆ =0.412.... ……… …(5)

The Rectangular Microstrip Patch Antenna is designedonFR-4 lossy substrate with εr = 4.3 and height from theground plane d= 1.6mm.The Length and width of RMPAare L=47.9563mm, W=61.4295mm respectively, whichare calculated from the formulae discussed in parametricanalysis section. For cut width, cut depth, length of transmission line and width of the feed, some specific

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values have been chosen to obtain the resonatingfrequency of the proposed antenna at 1.47 GHz. Thesevalues can be varied to change the resonatingfrequency.The parameter specifications of rectangulamicrostrip patch antenna are mentioned in Table 1.

Return loss

and Impedance Bandwidth o

Rectangular Microstrip Patch Antenna is shown in Figure3. According to this figure return loss and bandwidthare -10.447dB and 10MHz respectively.

In this paper the proposed metamaterial structure isintroduced to form the superstate of a rectangularmicrostrip patch antenna (Figure 2). The requiredspecifications of this design are shown in the Figure 4.

Nicolson-Ross-Weir (NRW) approach

The values of permittivity and permeability affect thepotential parameters like return loss and radiation patternof an antenna, this is the reason why these values arecalculated. For obtaining the values of permeability andpermittivity different methods can be used, some of themare Nicolson-Ross-Weir (NRW), NISTiterative, Non-iterative and Short circuit techniques. In this workNicolson-Ross-Weir (NRW) technique (Mazid et al.2008; Ziolkowski, 2003) has been used to obtain thevalues of permittivity and permeability as this is a verypopular technique to convert S-parameters due to thefact that this technique provides easy as well as effectiveformulation and calculation. All these methods discussedabove required S-parameters for obtaining the values ofpermeability and permittivity.

Here in this work for extracting the S-Parameters

proposed metamaterial structure is placed between thetwo waveguide ports (Hrabar and Bartolic, 2003) Hrabaret al., 2005) at the left and right hand side of the X axisas shown in Figure 5. In Figure 5, Y-Plane is defined asPerfect Electric Boundary (PEB) and Z-Plane is definedas the Perfect Magnetic Boundary (PMB), which createsinternal environment of waveguide. The simulated S-Parameters are then exported to Microsoft ExceProgram for verifying the Double-Negative properties othe proposed metamaterial structure (Garg et al., 2012).

Equations used for calculating permittivity and

permeability using NRW approach (Garg et al., 2012Majid et al., 2009; Samadhiya and Verma, 2012)

= .()..()…………………………….…… (6)

Ɛ = .()..()....…………………………….. (7)

= + …………………………. (8)

= − …………………………. (9)



015 Res. J. Phy. and Appl. Sci.

Table 1. RMPA specifications.

Dimensions Unit

Dielectric Constant (ԑr) 4.3 -

Loss Tangent (tan ∂) 0.02 -

Thickness (h) 1.6 mmOperating Frequency 1.9275 GHz

Length (L) 35.4413 mmWidth (W) 45.6435 mm

Cut Width 5.0 mmCut Depth 10.0 mm

Path Length 33.82175 mm

Width Of Feed 3.009 mm

Figure 2. Rectangular Patch Antenna at 1.47 GHz.

Figure 3. Simulation of Return loss and impedance

bandwidth of Rectangular Microstrip Patch Antenna.

Where;εr = Permittivity μr = Permeabilityc= Speed of Lightω = Frequency in Radiand = Thickness of the Substratei = Imaginary coefficient = Voltage Maxima = Voltage Minima

Figure 4. Design of proposed metamaterial structure.

Figure 5. Proposed metamaterial structure between the two

waveguide ports.

For satisfying Double Negative property, the values ofpermeability and permittivity should be negative withinthe operating frequency range. The obtained values othese two quantities from the MS-Excel Program aregiven in Table 2 and 3, whereas Figure 6 and Figure 7shows the graph between permeability and frequencyand permittivity and frequency respectively.Rectangular Microstrip Patch Antenna with Proposedmetamaterial is given below in Figure 8.Return loss and Impedance Bandwidth of Rectangulamicrostrip Patch Antenna with proposed metamateriastructure is shown in Figure 9. According to this figurereturn loss and bandwidth are -25.772dB and 32.3MHzrespectively.

From Figure 3 and 9 it has been observed that thereturn loss has significantly reduced by 15.33 dB andbandwidth has increased by 22.3 MHz by incorporatingproposed metamterial structure with RMPA.

The radiation pattern of an antenna is generally itsmost basic requirement because it determines thedistribution of radiated energy in to the space.Gaindepends on directivity and directivity is totally depends onthe shape of the radiation patterns of an antenna. TheRadiation Pattern of the RMPA operating at 1.47GHz isshown in Figure 10. This shows that the directivity is



Garg et al. 016

Table 2.Obtained values for Permeability versus Frequency from the MS-Excel program.

Frequency(GHz) Permeabilit y [µr] Re [µr]

1.4699998 -374.607339659479+3.45618384526422i -374.607

1.472 -366.919300540636+2.86948228882631i -366.919

1.474 -360.018040176235+0.731096575437185i -360.0181.476 -354.394182884314-2.51093557285303i -354.394

1.4779998 -350.339037560325-6.30143536916735i -350.3391.4799998 -347.928829930846-10.0203032019875i -347.929

Table 3. Obtained values for Permittivity versus Frequency from the MS-Excel program.

Frequency (GHz) Permitt ivi ty [Ɛr] Re [Ɛr]

1.4699998 -29.0168213445691-0.0961040378037559i -29.0168

1.472 -28.3655580620901-0.0176464610117287i -28.3656

1.474 -27.6834397492795+0.0364691431149244i -27.6834

1.476 -26.9840623306393+0.0534416269108215i -26.98411.4779998 -26.284494584046+0.0279434158733502i -26.2845

1.4799998 -25.6015651919585-0.0379574358370813i -25.6016

Figure 6. Permeability versus Frequency graph.

Figure 7. Permittivity versus frequency graph.

6.575dBi, whereas Figure 11 shows that the directivity of the RMPA with the proposed metamaterial structurewhich is 6.604. These results are showing that there isamelioration in directivity of RMPA by incorporatingproposed metamaterial structure.

Figure 8. Rectangular Microstrip Patch Antenna withproposed metamaterial structure.

Figure 9. Simulation of Return Loss andimpedance bandwidth of RMPA with proposedmetamaterial structure.

Smith et al., (2000) charts play a very important role foran antenna as it provides valuable information about




Figure 10. Radiation pattern of a Rectangular Microstrip Patch

Antenna.

Figure 11. Radiation pattern of RMPA with proposed metamaterialstructure.

Figure 12. Smith chart of Rectangular Microstrip Patch Antenna.

Figure 13. Smith chart of RMPA with proposed metamaterial

structure.

Figure 14. Fabricated rectangular microstrip patch antenna on

PCB.

Figure 15. Fabricated metamaterial structure on PCB.

Figure16. Setup for measurement of antenna parameters.

Figure17. Combined simulated and measured result of proposed

antenna.

impedances at different frequency point so that decisionabout the impedance matching can be taken. FromFigure 12 and 13, it is clear that the RMPA with theproposed metamaterial structure provides bette



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Table 4. Variation in metamaterial substrate size.

Metamaterial substratesize (mm×mm)

ReturnLoss (dB)

Bandwidth(MHz)

Directivity (dBi)

122.85 ×95.91 -23.923 29 6.806

120 ×94 -31.935 30.5 6.726118 ×92 -22.041 32.9 6.429

116 ×93.4 -25.923 32.2 6.613116×93.2 (Proposed size) -25.772 32.3 6.604

124×96 -23.489 28.9 6.809

126 ×98 -22.122 28.5 6.822

impedance matching at 1.47GHz, when compared toRMPA alone.

In this work metamaterial substrate size has beenvaried to see its effect on patch antenna parameters likereturn loss, bandwidth and directivity. These variations inmetamaterial substrate size along with the values of patch antenna parameters are shown in table 4. Initially

the dimension of the metamaterial substrate was122.85mm ×95.91mm, which is equal to the substratesize on which patch has been designed.It is clear fromthe table 4 that, if the metamaterial substrate size isvaried then due to this variation patch antennaparameters are also varied.

FABRICATION, TESTING AND EXPERIMENTALRESULTS

Return loss patternof RMPA with the proposedmetamaterial structure within the simulated frequencyrange given in Figure9 has been obtained from CST-MWS software, for verifying this result,hardware hadbeen fabricated on PCB. RMPA and proposedmetamaterial structure after fabrication on PCB havebeen given in Figure 14 and 15.After the fabrication of antenna the antenna parameters like return loss andbandwidth are measured on the spectrum analyzer. Thesetup which is used for antenna parametersmeasurement is shown in Figure16.Figure17 shows the Simulated and Measured result of proposed antenna.According to this graph the return lossand bandwidth at 1.47 GHz are -24.4dB and 29.835MHz(approximately) for fabricated antenna. This shows thatthere are very less variations in practically measured

results and simulated results of RMPA incorporated withproposed metamaterial structure.

Conclusion

On the basis of the simulation results it is observed thatthe minimum return loss obtained at the design frequencyfor the RMPA with proposed metamaterial structure is -25.77 dB and bandwidth is 32.3 MHz this is remarkableimprovement in L-band (1-2GHz), when compared to the

results of RMPA alone. It is clearly observed that thereturn lossbandwidth and directivity has improvedsignificantly by incorporating the proposed metamateriastructure at 3.2 mm layer from the ground plane of theantenna. Along with these improvements thisstructuresatisfies Double Negative property within thesimulated frequency range.

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