DESIGN OF HYBRID COUPLERCONNECTED HEXAGONAL

FRACTAL PATCH FOR VARIOUSWIRELESS APPLICATIONS

A.Sahaya Anselin Nisha1, R.Narmadha2,1,2Faculty of Electrical and Electronics Engineering,

Sathyabama Institute of Science and Technology,Chennai, India.

anselinnisha.ece@sathyabama.ac.in,narmadha.enc@sathyabama.ac.in

June 21, 2018

Abstract

Generator and turbine units are the major machineriesused in the wind energy conversion system. The efficiency ofsuch system depends greatly on the generators performance.Switched Reluctance Generator (SRG) is slowly replacingconventional induction and permanent magnet synchronousgenerators in the area of wind energy generation system.This paper presents the fuzzy logic based inductance pro-file evaluation technique for SRG. The main objective of thiswork is to determine the suitable fuzzy membership functionfor inductance profile estimation. The various membershipfunctions such as Trapezoidal, Gbell, Gaussian, Psigmoidand Triangular functions are used to develop the non lin-ear inductance pattern for SRG. The results of inductanceprofiles estimated from all these membership functions arecompared, analyzed and presented in detail. From the anal-ysis of results, it has been proved that the triangular mem-bership function has developed a good inductance profile

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compared with the other functions. The high non-linearitynature of SRG is well handled by triangular membershipfunction. The developed FIS for SRG is certain to be aprospective candidate in real time wind energy conversionsystem.

Keywords: Fractal Antenna, HFSS, Hybrid Coupler,Patch Antenna, Radiation pattern, Return loss.

1 INTRODUCTION

Fractals are a bend or geometrical figure, which has similar pat-terns happen again at progressively smaller scales. Fractal hascompact physical shape with electrically long curves due to spacefilling property. Different types of fractal shapes are available forexample Koch curve [1], Minkowski [2], Hilbert Curve [3], M. Susila[4] etc. Hybrid Minkowski fractal antenna for GPS system withdual frequency is achieved by Thanh Nghia Cao and Wojciech J.Krzysztofik [5] and miniaturization is done. The iteration order islimited to the complexity of the design because as the number ofiterations increases a more complex structure that is difficult to fab-ricate is formed [6]-[11]. With the evolution of antenna theory newdesign concepts of antenna have been introduced. By using fractalgeometry multiband antenna can be constructed and this is knownas Fractal Antenna. It is more than a decade, fractal geometriesare being applied in the design of passive components in the RF(radio frequency) and microwave domain. This geometry came into its existence due to B.B. Mandelbrot in the year 1975 [12]. Thisintensive study was being conducted in 1970s. Later in the midof 1990s, it was seen that the properties of such geometry couldbe used to design frequency selective surface, multiband antennaand also new configurations of antenna array. Several fractal basedantenna geometries have been reported in recent years [13, 14].

Coupler is one of the most popular passive circuits used in mi-crowave and millimeter-wave applications. It gives equal ampli-tude and phase outputs within the designed operating frequencies.These passive components are commonly used in variety of appli-cation such as mixers, phase shifters, power amplifiers and bridgingmany microwave circuits [15]. The hybrid couplers are designed us-ing three main topologies. They are branch-line, coupled line and

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Figure 1: Proposed design of hybrid coupler

Figure 2: Geometry of proposed microstrip patch antenna

patch-line structure. Each topology has its own advantages anddisadvantages. In a branch-line structures stubs are loaded on theconventional branch line sections to realize dual-band operation. Inother way, additional pairs of cross coupling and transmission linesections are to be added to the conventional branch line couplerto enable dualband operation [16-21]. In this paper we proposed anovel techniques that fractal antenna is fed by hybrid coupler andanalysed for wireless applications.

2 ANTENNA DESIGN

The dual fed circular polarized microstrip patch antenna is etchedon a FR4 epoxy with a height of 1.6mm. Ground plane length

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and width is taken as 37.9x47.6mm2. The operating frequency ischosen to be 2.4 GHz. The proposed hybrid coupler along with thedimensions is shown in Figure 1. The geometrical configuration ofthe suggested antenna is shown in figure 2. The antenna is fed bydual feed by using hybrid coupler. By adding the fractal geometrythe resonant frequencies are being shifted towards right side.

The design procedure for fractal structure is shown in figure3. The basic unit of fractal structure is a hexagon. The primaryhexagonal shaped patch is having a side length of 8mm. Fromthe hexagonal patch, six equilateral triangles of side 4mm is takenout to obtain first iteration. Then six equilateral triangles of sidelength 2mm is taken out which results in second iteration. Thensix equilateral triangle of side 1mm is taken out which results inthird iteration.

Figure 3: Various iterations of hexagonal shaped fractal antenna

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3 SIMULATION ANDMEASURED RE-

SULTS

The simulated return loss characteristics of the proposed antennaare shown in figure 4. From the return loss plot it is observed thatthe proposed design is resonating at five different frequencies forall the iterations. A comparison has been made for different pa-rameters like resonant frequency, return loss and gain for all theiterations and it is shown in table 1. The minimum return lossobtained from all the bands is found to be -27dB. By adding thefractal geometry to the hexagonal patch it is observed that thefrequency is slightly being shifted towards lower frequency side.For the first three iterations it is clear from the plot that there ispoor impedance matching and for the final iteration the impedancematching is improved. Apart from that a wider band has beenobtained in between the frequencies 3-4 GHz. Gain plots and radi-ation patterns of the proposed antenna are shown in figure 5 and 6.Comparing the gains of all the iterations it was observed that thegain has been improved for the final iteration at all the resonatingfrequencies.

Figure 4: Return loss plot for the proposed design

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Figure 5: Gain plots for the proposed antenna at (a) 2.5 GHz, (b)3.27 GHz, (c) 3.8 GHz, (d) 5.16 GHz and (e) 5.8GHz

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Figure 6: Comparison of simulation results for all the iterations ofproposed design

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Figure 7: Radiation patterns of proposed antenna at (a) 2.5 GHz,(b) 3.27 GHz, (c) 3.8 GHz, (d)5.16 GHz, and (e)5.8 GHz

Finally the prototype model is developed using Chemical vapourdeposition (CVD) method and the results are measured using Vec-tor Network Analyser shown in figure 7. The measured results areshows return loss at 2.8 GHz= -11.3 dB, at 4.16 GHz= -11.9 dBand at 5.24 GHz= -22.07 dB. Then comparison between measured

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and simulated result is done. These results are having very goodagreement between them which is shown in figure 8.

Figure 8: Measured return loss

Figure 9: Comparision between Simulated and Measured returnloss

4 CONCLUSION

In this paper a novel microstrip fractal antenna fed with hybrid cou-pler for different wireless applications is reported. Three iterationsof antenna are designed and various parameters such as return lossand gain are observed and on comparision with each other it showsthat impedance matching was improved for final iteration and along

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with it gain has been improved. So the proposed antenna is atrrac-tives and can be practical for various wireless applications.

References

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