Design of Dual-band Textile Antenna for 2.45/5.8-GHz Wireless ...

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[5] M. Mantash ; A. C. Tarot ; S. Collardey ; K. Mahdjoubi , “Zip based monopole antenna for wearable communication systems”, Antennas and Propagation ...
Design of Dual-band Textile Antenna for 2.45/5.8-GHz Wireless Applications Ameni Mersani and Lotfi Osman Department of Physics, UR "CSEHF" 13ES37 Faculty of Sciences of Tunis, University of Tunis El Manar, 2092 Tunisia [email protected], [email protected] Abstract—Microstrip patch antennas are widely used in microwave applications. The substrate used in their realization is a key parameter. On one hand, it may be considered as a technological level to ensure good performance (efficiency, bandwidth, radiation, ...). On the other hand, speaking of the economic side, it may be used in order to obtain cheap antennas. In this work, we are interested in the use of two different types of substrates: polyester and jeans cotton, and two different types of conductive textile materials (Electro-textile) which are Pure Copper Polyester Taffeta Fabric and Zelt for the realization of Wearable antennas. The antenna consists of a rectangular planar patch element embedded with L shaped slots and stair shape slot in the middle of the patch element. This antenna, fed by a coplanar waveguide (CPW) is intended to be integrated and carried in a person's clothing. The proposed antenna is simulated and the results show that the operating band covers 2.25 GHz to 2.74 GHz and 4.3 to 6.8 GHz corresponding to the WLAN and WiMAX bands.

and Voltage Standing Wave Ratio (VSWR) [3]-[4]. Finally, some formulas to predict the antenna dimensions are given. II. MATERIAL SELECTION AND ANTENNA DESIGN The proposed textile antenna is illustrated in Fig. 1.

Keywords-CPW antenna; textile Substrate; electro-textile; WLAN; WiMAX.

I. INTRODUCTION Wearable antenna, also known as textile antenna, is well-known for its attractive merits such as low profile, low weight, flexible, washable and more importantly, easy to be integrated within everyday clothing [1]. The substrate plays an essential role in manufacture the patch antennas. It is necessary to choose a substrate which is not fragile with low dielectric constant to ensure greater efficiency, high bandwidth and good radiation of the antenna. The characterization of material proprieties is required so as to design an efficient antenna using textile material with substrate. Advances in wireless communication technologies are placing greater demands on higher antenna impedance bandwidth and smaller antenna size [2]. The proposed antenna has been used in WLAN and WiMAX because of some good features like low cost, low profile and easy to fabricate [6]-[7]. The currently popular designs suitable for WLAN operation in the 2.4 GHz (2.4–2.484 GHz) and 5.2/5.8GHz (5.15–5.35 GHz/5.725–5.825GHz) bands and WiMAX operation in the 2.5/3.5/5.5 GHz bands have been reported in [8]-[9]. In this paper a new textile antenna is designed and simulated to cover two bands of WLAN and WiMAX Application. The performance characteristics of two antennas made from two substrates using different electro-textiles have been presented. The characteristics that have been studied are reflection coefficient, radiation pattern

Figure 1. Geometry of the proposed antenna.

The basis of the antenna structure is chosen to be a rectangular patch element. In the basic design of a patch antenna, equations (1), (2), (3), (4) and (5) are used to calculate preliminary dimensions of the radiating element. As can be seen, the width W depends on the material used in designing the printed antenna and the operating frequency. Hence, the value of L can be calculated as [10].

εr =

+

-

(

. )( .

L= 0.412

.

(

) )

)(

)

The effective length of the patch is expressed as Leff = L+∆L The formula for Patch width is given by W=



(

(1)

)

(2)

(3)

(4)

And the length is given as L=



(5)

Therefore, Textile and Electro-textile are important components in wearable antenna fabrication. Electro-textile is obtained by interleaving normal fabric with conductive metal/polymer [5]-[13].

perfect matching (S11< -10) for different antennas which checks the position of the 50Ω point.

The substrates selected for this work are polyester and cotton. The properties of these substrates and electro-textiles are listed in Tables I and II, respectively [1]-[11]. TABLE I. DIELECTRIC PROPERTIES OF SUBSTRATE MATERIALS Substrate

Jeans cotton

Polyester

Loss tangent

0.033

0.0044

Permittivity

1.67

1.748

Thickness (mm)

2.84

0.28

TABLE II. CHARACTERISTIC OF THE CONDUCTIVE TEXTILE Figure 2. Simulated return loss for different textiles substrates. Pure Copper Polyester Taffeta Fabric

Zelt

Surface Resistance (Ω)

0.05

0.05

Conductivity (105 S/m)

2.5

1.749

Thickness (mm)

0.08

0.0635

Electro-textile

A.

Three antennas chosen with different textiles and electrotextile substrates are in good agreement at lower frequency band 2.45 GHz while at 5.8 GHz, Jeans antenna simulated bandwidth for a return loss of -10 dB is less than the Polyester antenna. B.

The antenna dimensions are given in Table III. TABLE III. ANTENNA D IMENSIONS

Parameters

Value (mm)

W

24

L

29

Gr

10.37

Fs

3

Ls1

10.5

Ls2

6.5

Ws

19

Li

4

Wi

4.25

G

3.25

III. RESULTS AND DISCUSSION The antenna was simulated using CST software. The simulation results are presented in Fig. 2. The parameters of the textile antenna for different substrates are varied so as to obtain the desired antenna characteristic which operates at 2.45 GHz and 5.8 GHz. The simulation results show a

Return Loss

Radiation Patterns

The radiation patterns of the antenna on the two substrates and electro-textile are similar (Table IV), but in future simulation, we will choose the jeans to avoid any kind of dimension variation due to the stretching and compression. Zelt fabric is considered better compared to others because: low surface resistivity 0.01 Ω/sq and high conductivity 1 e+0. 006 S/m. TABLE IV. SIMULATED AND MEASURED RADIATION PATTERNS OF THE ANTENNA FOR DIFFERENT SUBSTRATES

Substrate

Realized gain (dB)

Directivity (dBi)

2.45 GHz

5.8 GHz

2.45 GHz

5.8 GHz

Polyester- Pure Copper

0.591

2.36

2.51

3.22

Jeans cottonZelt

0.622

2.61

2.41

3.68

Jeans cottonPure Copper

0.644

2.39

2.67

3.68

demonstrates that the VSWR value lies below 1.7 at both resonant frequencies as desired. IV. CONCLUSION In this paper, an investigation of the effect using different substrates and electro-textiles is presented. The proposed antenna is successfully capable to cover dual band frequency (2.45 GHz and 5.8 GHz). The proposed wearable textile antenna has the potential to integrate on the garment and can be used for WIFI and WiMAX applications. REFERENCES [1]

[2]

[3] Figure 3. Simulated radiation patterns.

The simulated results of the textile antenna radiation patterns depicted in Fig. 3 show that the directivity is omnidirectional. Therefore a metamaterial structure is needed to change the radiation pattern more directional hence less radiation exposure to the human body and also to increase the antenna performance. C.

VSWR Parameter

[4]

[5]

[6]

[7]

[8]

[9]

[10] Figure 4. Plot of VSWR vs. frequency at 2.45 GHz. [11]

[12]

[13]

Figure 5. Plot of VSWR vs. frequency at 5.8GHz.

The VSWR vs. frequency graph of the proposed antenna is shown in Fig. 4 and Fig. 5 respectively, which

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