MINIATURISATION OF PATCH ANTENNA USING NOVEL FRACTAL GEOMETRY

Volume 7, Issue 1, Jan-Feb 2016, pp. 63-74, Article ID: IJECET_07_01_007 Available online at

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MINIATURISATION OF PATCH ANTENNA

USING NOVEL FRACTAL GEOMETRY

Padmavathi C

Department of Electronics & Communication Engineering, ACED Alliance University, Bangalore, Karnataka, India

ABSTRACT

In the Field of low profile antenna micro strip patch antennas have attracted many researchers due to small size and low cost of fabrication. One of trending member of new designs is Fractal antenna. Fractal shapes are recursive/repetitive self-similar geometries, due to this self-similarity they can provide high gain, multiband, wideband solutions and design miniature antenna. Fractal shapes are widely used in computing, analysis and design; recent trends suggest positive outcomes of using fractal shapes in electromagnetics and communication system. In this paper Jerusalem cube fractal shape is introduced in probe fed conventional patch antenna for L1 band. A dual band antenna resonating at 1.41 GHz (L) and 3.37 (S) GHz, band is constructed using said fractal shape. The comparison of Return loss, Gain, VSWR, % miniaturisation and radiation patterns are shown with conventional patch antenna. Analysis is done on RT duroid 5880 with dielectric constant εr = 2.2. The novel fractal antenna is designed, simulated using an soft HFSS 13.0.

Key words: Fractal Antenna, Jerusalem Cube Fractal, Miniaturisation, Patch Antenna

Cite this Article: Padmavathi C. Miniaturisation of Patch Antenna Using Novel Fractal Geometry. International Journal of Electronics and

Communication Engineering & Technology, 7(1), 2016, pp. 63-74.

http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=7&IType=1

1. INTRODUCTION

Advancements in Wireless communication have paved the way for many researchers to make the system smarter and smarter. In most of RF and Microwave applications antenna plays an important role, As per the IEEE std.145-1983 the antenna is considered as means for radiating or receiving radio waves. Theoretically they are the transducers which convert RF signal into Electromagnetic waves and viceversa. Antenna in early days used to be voluminous and high profile.

Technically, the need is for wider bandwidths, higher gain, smaller size and multiband abilities in antennas. Cost too, is a factor of consideration. Hence low profiles and less complexity in fabrication are areas of interest in antenna research. Printed antennas have capabilities of answering all these demands. In addition, printed antennas can be smaller in size and can be used for smallest applications to the largest ones. These printed antennas are widely used in mobile and satellite communication, the patch antenna allows modifications in their design which can make them suitable for wideband and multiband applications and also help in miniaturisation. These micro strip patch antenna are light weight, low cost, easy to design / manufacture, on the other side these antenna are low profile, low power handling capabilities, low efficiency and are not suitable for high bandwidth applications these limitations is overcome by Fractal antenna.

The method to design patch antenna with better properties is to use fractal shapes in design [9]-[12]. Fractal is an object achieved by recursive arrangement of a shape or pattern keeping it same at every scale, they are space filling contours and offers longer electrical length in smaller spaces this help in antenna miniaturisation, offering multiple resonant frequencies. The term fractal means uneven or broken, the geometries are complex and cannot be defined using Euclidean geometries and mathematically infinite structure. The conventional methods available for antenna miniaturisation does not maintain good characteristics after certain percentage of miniaturisation and losses its performance. Fractals can help enhancing antenna performance in terms of Gain, Return Loss, Side Lobes Reduction, etc. If we can prepare an antenna with enhanced transmission / reception of GPS signals, it would help in betterment of number of devices. The research in Fractal Antennas is still in its emerging phase.

Very promising results are seen for further studies in enhancement of antenna characteristics. Along with Gain and Return Loss enhancement, using fractals not only creates other frequency bands but shifts the original frequency down. This can be widely utilized in antenna miniaturization. Literature shows more use of Koch and Sierpinski models of fractal shapes in monopole, dipole and patch antennas. Wide scope of combining more than one GPS frequency or combine GPS with classical GSM or ISM application is there using fractal shapes. Some of the fractals like Koch curve and Sierpinski gaskets are, even at present, widely used to create multiband and wideband antennas. Using Sierpinski Carpet fractal, up to 14 % of miniaturization in conventional L1 band antenna (1.575 GHz) was achieved. Up to 19 % of miniaturization is achieved using another fractal shape of Koch Curve / Koch Snowflake.

In this paper an antenna which resonates at L5 (1.17 GHz) GPS frequency band is designed. The primary model for implementing the fractal is designed using conventional patch antenna designing parameters. The results show clear resonance at L5 band with positive gain value and a reasonably good radiation pattern. The co-ax probe feeding method is tested and results are extracted. In this paper a dual band antenna which resonates at L and S band with Probe fed technique along with up to 20% miniaturization is achieved using Jerusalem Fractal with promising Return Loss as well as Gain values. Radiation patterns and VSWR plots are also extracted for each

2. MICROSTRIP PATCH ANTENNA

Micro strip patch antenna is a printed metal patch on ground dielectric substrate, patch radiates depending on its length, width, feed location, gain, radiation pattern, dielectric constant of substrate. The patch antenna operating frequencies range from 900 MHz or lower to 30-40 GHz and have three layers top metallic layer is the patch which radiates, bottom metallic layer is the ground, and middle layer is dielectric. The resonating frequency of antenna depends on length of patch and dielectric constant of substrate along with other parameter [16].

Figure 1 Micro strip patch antenna

The patch is made of conducting radiating materials such as gold, copper etc. The Radiating metallic patch and the probe feed lines are usually photo etched on the dielectric substrate. Micro strip patch antenna radiate mainly because of the fringing fields effect between the patch edge and the ground plane. For a rectangular patch, the length L of the patch is usually 0.3333λ0<L<0.5 λ0, where λ0 is the free space wavelength. The patch is selected to be very thin such that t << λ0 (where t is the thickness of patch). The height h of the dielectric substrate is usually 0.003 λ0 ≤ h ≤ 0.05 λ0. The dielectric constant of the substrate (εr) is typically in the range 2.2 ≤ εr ≤ 12.

2.1. Conventional Rectangular Patch – Co-ax Feed

Since the length of the patch and operating frequency has a direct relation, any of them has to be defined in the beginning. We will try making an Antenna for L5 band applications i.e. 1.17 GHz of operating frequency. The antenna Design Equations are f0 = 1.17 GHz

0=c/ 0 = 256 mm εr = 4.4 for Material FR4

h = 1.56 mm, height of substrate For Width of Patch,

=

=

= 78.023 mm For effective relative permitivity in the medium

ε

+

Substituting the values we get,

ε

For the actualwavelength in the medium, λ =

= 124.61mm Effective length can be found as Leff =

=

62.40mm Difference due to fringing field can be expressed as

ΔL = 0.412h

= 0.641mm The actual patch length

L = Leff - 2ΔL = 61.11mm Ground plane dimensions are

LG = 6(h) + L = 70.47mm, WG = 6(h) + W = 87.38mm

2.2. Simulations of coventional rectangular patch antenna

(a) (b)

(c)

Figure 2 Antenna for L5 Frequency with Co-ax Feed (a) Top view (b) Side view (c) Angular view

Figure 3 Return loss of the reference antenna for L5

From Fig.3 it is seen that the antenna resonates at 1.172 GHz which is the L5 band used for aeronautical navigation along with L1 and L2. The return loss value at the said frequency is less than -35 dB which shows good VSWR.

Figure 4 Gain plot of the reference antenna for L5 From Fig.4 the positive gain value of 1.89 dB is seen.

3. DESIGN OF ANTENNA

3.1. The Jerusalem Cube Fractal

The Fractal Jerusalem curve is not widely used in printed antenna design is mostly used in 3D modelling. A novel dual band antenna is conceptualised, simulated and compared using Jerusalem cube fractal shape on patch. The fractal shape is simple and easy to design compared with other fractals, the fractal shape is made on a square or a rectangular patch, the whole patch is made into 9 parts and + cross sign is cut out of the centre square, this is repeated up to number of levels. In this fractal design, a cross sign is used, the curve is applied at the edges of conventional patch antenna as slots in shape of cross used in Jerusalem fractal.

Figure 6 Jerusalem Fractal up to three levels

3.2. Dual Band Novel Fractal antenna Design

The specifications of the antenna are given as F0 = 1.57 GHz (L1 Band), resonating Frequency, εr = 2.2 for Material Rogers RT / Duroid 5880, h = 1.56 mm, height of substrate, L = 59.1 mm (W=L, since square antenna), length of the edge of square patch LG = 80 mm (WG = LG), length of the edge of square ground plane, Length of each segment in Jerusalem Fractal L1 = 10 mm, Feed Location fx = 11 mm from centre for impedance matching, The width of single side of cross is 3.33mm, the feed location is 14.6mm to ensure maximum power transfer, and size of slot is cut from the patch in square of 10mm*10mm

(a)

(b)

Figure 7 (a) Conventional Patch Antenna (b) Jerusalem Slots on Patch Antenna

(a) (b)

(c)

Figure 8 (a) Conventional Antenna (b) Antenna with Jerusalem Slots (c) Patch Antenna using Jerusalem Fractal as slots

From Fig.9 it reveals the antenna resonates at L (1.412 GHz) band and S (3.377 GHz) band.

Figure 9 Return Loss plot of Jerusalem Fractal Antenna

(a) For 1.412 GHz

(b) For 3.377 GHz

Figure 11 Radiation Patterns at individual resonant frequencies on Jerusalem Fractal Antenna The radiation patterns show that both the frequencies show symmetric response over the theta. Only for 3.377 GHz, the Phi = 90 plot is different in nature from others and shows response similar to an isotropic antenna.

Figure 12 VSWR plot of the Jerusalem Fractal Antenna

The VSWR plot shown above is in synch with the Return Loss plot. Since the RL value of the first resonant frequency was high, the VSWR plot shows 3.31. However, for the second resonant frequency, it shows only 1.56 value of VSWR which can be considered as good.

Figure 13 Comparison of Return Loss of Conventional (L1) band and Jerusalem Fractal

Antenna (L and S) band

The return loss plot shows clear shift in frequency from 1.57 GHz of conventional antenna to 1.412 GHz of Jerusalem fractal. The 1.5 GHz shift in frequency can provide a miniaturization of considerable level.

Figure 14 Gain comparisons of Conventional Antenna and Jerusalem Fractal

Fig.14 shows that gain value of both the bands is considerably good compared to that of the conventional antenna.

Table 1 shows the summary of the Return Loss, Gain, and VSWR and Miniaturization level of both the antennas.

Table 1 Results and Miniaturization of Jerusalem Fractal Antenna

Antenna Type Results

Return Loss (dB) Total gain (dB) VSWR Miniaturisation (%) Conventional Antenna (1.57 GHz) -20.00 7.35 1.5650 0 Jerusalem Fractal Band 1

(1.412 GHz) 5.41 6.42 1.4120

20%

4. CONCLUSION

The novel antenna is designed and simulated using HFSS 13.0. Coaxial probe feeding is used in designing of an antenna. In the paper the dual band antenna resonating at L and S Band using Jerusalem fractal as slots in patch for miniaturisation is proposed. The work shows the positive results of using this fractal shape on conventional patch antenna. The results show that dual band antenna had better gain and improved miniaturisation characteristics suitable for GPS and navigation applications. There lies immense scope of trying further various fractal geometries into patch antenna. Selective geometries cam be evaluated to achieve further better results compared to present ones. Also, present antennas can be tuned for further optimization of results.

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