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ANALYSIS OF TRIANGULAR MICROSTRIP

PATCH ANTENNA WITH KOCH BOUNDARY

FOR WLAN APPLICATION

1M.Arulaalan and 2L.Nithyanandan1Pondicherry Engineering College, Pondicherry

Email: [email protected] Pondicherry Engineering College, Pondicherry

Email: [email protected]

Abstract A triangular Microstrip patch antenna with and without Koch boundary for

Wireless local area networks (WLAN) is proposed. The inset fed feeding technique is chosen

because it provides good impedance matching. The performance of the inset fed triangular

Microstrip patch antenna is improved by the addition of Koch boundary. With the Koch

boundary of single iteration added to the antenna the resonant frequency of the antenna is

maintained with improved return loss and gain. Details of the proposed antenna with Koch

boundary are described and the experimental results are presented and analyzed with the

antenna without Koch boundary. There is a good agreement between the simulated and

measured results. Results show that the antenna gain and return loss is improved by the

addition of Koch boundary

I ndex TermsMicrostrip patch antenna, inset fed, return Loss, WLAN, Koch.

I.INTRODUCTION

WLAN applications has become more popular especially those operating in ISM band. Printed

antennas shown to be promising for WLAN applications. They are easy to fabricate at low cost. Microstripantennas in general have the attractive features of low profile, light weight, easy fabrication. However,Microstrip antennas inherently have a narrow bandwidth and low gain. The Koch fractal geometry was firstintroduced by Von Koch [1]. The fractal geometry was applied to monopole, loops, patch, antenna arrays and

dipoles. If the return loss of the antenna is improved the gain of the antenna increases. Several research arecarried out for improving return loss and gain in a Microstrip antenna and most of the research targeted onrectangular and square patch antenna. In this paper triangular Microstrip inset fed antenna is chosen and thereturn loss is improved by adding additional structure, the Koch boundary. The triangular patch antenna ischosen because it occupies less space compared to rectangular patch antenna. For the improvement of returnloss and gain several researchers modified the patch shape which resulted in complexity. For improving

return loss, application of fractal geometries has been shown to enhance gain and directivity [1]. Fractal slotantennas are used to improve the gain and directivity [2]. However these techniques increased the antennasize. Partial Koch boundaries with two iteration and air gap are introduced in a triangular patch antenna toimprove the return loss and gain [3]. The slotted triangular patch shows lower reflection loss compared to aconventional triangular patch antenna [4] .This technique introduced a complex structure around thetriangular patch which is difficult to fabricate. The return loss and gain in this paper is improved with single

Int. J. of Recent Trends in Engineering & Technology, Vol. 11, June 2014


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iteration of Koch boundary thereby reducing the complex structure with higher iteration. In this paper design,simulation and fabrication results of a simple Microstrip patch antenna based on first iteration of Koch shapeis presented. The design, simulated results and measured results are discussed in section II and III

II. ANTENNA GEOMETRY AND DESIGN

A.Equilateral Triangle Microstrip Antenna Design

The triangular patch antenna is a good replacement for rectangular patch antenna due to similar radiationcharacteristcs and triangular patch antenna occupies smaller area on substrate than other existing shapes likerectangular and circular.FR4 substrate is chosen to fabricate the antenna with the thickness of t=1.6mm anddielectric constant value of r =4.4.The FR4 substrate is chosen because of low cost , zero water absorptionand good mechanical strength. For an equilateral triangular microstrip antenna the value of a as shown in

Fig. 1is obtained from the cavity model with perfect magnetic walls [5,6].

Figure 1. Equilateral triangular Microstrip patch antenna

(1)

Where a=length of a side of the equilateral triangle in mm, C= velocity of electromagnetic waves in freespace light and r = Relative dielectric constant of the substrate (FR4).

The feed technique plays an important role in the design of Microstrip patch antenna. The inset fedfeeding technique is chosen because the input impedance of the antenna can be easily controlled by varyingthe feed length to achieve 50 impedance.

For calculating the inset fed length (y0) the inset fed rectangular Microstrip antenna formula [7-9]

is chosen which is around Yo = 8mm and the inset fed width Wi =3mm as shown in Fig. 2.The dimensions ofthe antenna are tabulated in Table I

Figure 2. Layout of the inset fed equilateral triangle Microstrip patch antenna.

=60

a


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TABLE I. THE DIMENSIONS OF INSET FED TRIANGULAR PATCH ANTENNA

B. Measured Results of inset triangular patch antenna

The inset fed triangular microstrip patch antenna is designed, simulated using AdvancedDesign System 2008 and fabricated using FR4 substrate. The antenna covers the frequency range of 2.4GHz(IEEE 802.11b). Fig. 3 shows the fabricated Inset fed triangular patch Microstrip antenna .Figs. 4 shows thesimulated and measured return Loss of Inset fed Microstrip antenna without Koch boundary. Return loss is ameasure of impedance matching. The antenna measurement is carried out using Rohde & Schwarz ZVH4.The parameters return loss and VSWR of the Microstrip antenna are measured using Vector network

analyzer.The simulated return loss is -19.44 dB and the fabricated antenna return loss is -16dB . Thesimulated resonant frequency of the antenna is 2.37GHz and the fabricated antenna resonant frequency is

2.51GHz. The measured impedance of the antenna is 51.The measured VSWR value is 1.39 as shown inFig.7 and gain of the antenna is 5.6dB with directivity of 5dB as shown in Fig.6 and Fig.8 shows the 2-Dradiation pattern of the antenna. The measured and simulated results difference is due to SMA Connector, thefeed position error, measurement and fabrication error.

Figure 3. Fabricated Inset fed triangular Microstrip

patch antenna.

1 1.5 2 2.5 3-20

-15

-10

-5

0

Frequency (GHz)

S11(dB)

Simulated

Fabricated

Figure 4.The simulated and measured return loss of inset fed

triangular patch antenna

Patch antennaParameters

L W a Yo Wi

Units in mm 32.3 3 39.5 8 3


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Figure 5.Current Distribution in inset fed triangular patch antenna Figure 6. Gain and Directivity of inset fed triangular

Patch antenna

Figure 7. Measured VSWR Figure 8. 2-D pattern of Inset fed patch antenna

III.TRIANGULAR MICROSTRIP PATCH ANTENNA WITH KOCH BOUNDARY

The Koch fractal curve is one of the most well known fractal shapes. Fractal shaped antennasexhibit some interesting characteristics, which correlate with their geometrical properties. The word fractal,derived from the Latin word fractus meaning broken, i.e., fragmented, fractional or irregular. A fractal is a

rough or fragmented geometric shape that can be subdivided in parts, each of which is a reduced size copy ofthe whole. Fractals are generally self similar and independent of scale. The main idea of using fractal

geometries in the design of microstrip antenna is to increase the effective electrical length through whichcurrent travels. There are an infinite number of fractal geometries available, but a few can be applied tomicrostrip antennas to observe their behavior particularly on the size reduction. Sierpinski carpet andSierpinski gasket antennas are familiar fractal geometries for their multiband operation [10]. The Koch curveis one of the most familiar fractal curves which can be used to reduce the size of the antenna. Fractalstructures are generally composed of multiple copies of themselves at different scales and the size of a fractal

is determined by the initiator and iteration number. Koch fractal geometry is one of the well known fractal


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shapes. The first iteration of Koch fractal is obtained by replacing the sides of an equilateral triangle by aKoch curve characteristics. Fig. 9 shows Koch curve for zero iteration. Fig. 10 shows Koch curve for oneiteration. Fig. 11 shows Koch curve for two iteration. With each iteration the length of Koch increases by one

third of its previous length. The Koch is constructed by adding smaller and smaller triangles to the structure

in an iterative fashion. In this paper to improve the antenna performance an inset fed triangular microstripantenna is chosen and return loss and gain is improved by adding Koch curve with single iteration on twosides of the triangular patch antenna and the antenna structure is modified by introduction of Koch curve. It isobserved that the 1/4.5 Koch patch has much improved return loss and gain compared to that of the inset fed

Triangular patch

Figure 9. Koch curve with zero iteration. Figure 10. Koch curve with one iteration.

Figure 11. Koch curve with two iteration.

The Koch curve with one iteration is applied to the two sides of the inset fed triangular patchantenna. The sides of the equilateral triangle a=39.5mm.The sides of the triangle is divided by 4.5, the valueis around 8.5mm which is used to form the Koch curve for single iteration.

A. INSET FED MICROSTRIP PATCH ANTENNA MEASURED RESULTS WITH KOCH BOUNDARY

The performance of the inset fed antenna is improved by the addition of Koch boundaryto the antenna .The antenna parameters return loss and gain is improved by the addition of Koch boundary.The inset fed triangular Microstrip antenna with Koch boundary is fabricated in a FR4 with thickness of1.6mm.The antenna operates for WLAN application. Fig. 12 shows the fabricated inset fed triangularMicrostrip patch antenna with Koch boundary .Fig. 13 shows the simulated and measured return Loss of

Inset fed triangular Microstrip patch antenna with Koch boundary. The return loss improved by -10dB by theaddition of Koch boundary on the two sides of triangular patch antenna and the antenna resonated in WLAN

frequency band of 2.47GHz. The gain of the antenna improved to 6.4 dB as shown in Fig.14.The impedanceof the antenna is 51 .Fig.15 shows the current distribution in the antenna with Koch boundary. The VSWR

value at the resonating frequency is 1.27 as shown in Fig.16. Fig.17 shows the 2D radiation pattern of theantenna.


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1 1.5 2 2.5 3-30

-25

-20

-15

-10

-5

0

Frequency (GHz)

S11(dB)

Fabricated

Simulated

Figure 12. Fabricated Inset fed Microstrip antenna Figure13.Measured and simulated reflection coefficient ofMicrostrip with Koch boundary antenna with Koch boundary

Figure 14. Gain and Directivity in inset fed triangular Figure 15.Current distribution in antenna with Koch boundary

patch antenna with Koch boundary


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[5] Jaswant.S.Dahele, Kai Fong Lee,on the resonant frequencies of the triangular patch antenna, IEEETransactions on Antennas and Propagation, vol-35, pp.100-101,Jan 1987.

[6]

Lee K.F, Luk. K.M and Dahele, Characteristics of the equilateral triangular patch antenna, IEEE Trans.,

vol.36, pp. 1510- 1518, Nov 1988.

[7]

Jeen-Sheen Rowand Yen-Yu Liou, Broadband Short-Circuited Triangular Patch Antenna,"IEEE Transactionson Antennas and Propagation, vol.54,pp. 2137-2141, July 2006.

[8] T. Samaras, A. Kouloglou, and J. N. Sahalos, A Note on the Impedance Variation with Feed Position of aRectangular Microstrip-Patch Antenna, IEEE Antennas and Propagation Magazine, vol.46, pp.90-92, April

2004.

[9]

Ying Hu, David R. Jackson, Jeffery T.Williams,Stuart A.Long, and Varada Rajan Komanduri,

Characterization of the Input Impedance of the Inset-Fed Rectangular Microstrip Antenna,IEEE Transactionson Antennas and Propagation, vol. 56, No.10, pp.3314-3318 October 2008.

[10] C.Puente-Baliarda, J. Romeu, R. Pous, and A. Cardama, On the behaviour of the Sierpinski multiband fractalantenna,IEEE Transactions on Antennas and Propagation, vol. 46, pp. 517524, 1998.

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