31978-1-4673-5513-1 ©2013 IEEE

Design a 3.5 slot Antenna using Coplanar Waveguide (CPW) for Dual Band Application

M.Z.A. Abd. Aziz, M. Md. Shukor, M.K. Suaidi, B. H. Ahmad, M. A. Othman, N. Hasan Center for Telecommunication Research and Innovation,

FKEKK, Univ. Teknikal Malaysia Melaka (UTeM), Melaka, Malaysia

mohamadzoinol@utem.edu.my

Abstract—The proposed antenna is designed to overcome the demand in dual band issues. The basic shape structures of antenna are designed at frequency 2.4 GHz based on radiating structure 5 and 5.2 GHz based on radiating structure 3. Then, the changes on the position of radiating structure 3 have been carried out to investigate the effect for dual band. The coplanar waveguide technique is used to design the basic structure 3.5 antenna to achieve dual band resonant frequencies. Then, the position of the radiating structure 3 is turned to 90° so that the resonant frequencies can achieve at 2.4 GHz and 5.2 GHz. The results from the simulations were then validated with experimental measurements of a prototype that has been fabricated. The return loss for both resonant frequencies are less than -10 dB where 90% of the input signal is transmitted and only 10% of the input signal is reflected back.

Keywords—coplanar waveguide, dual band, microstrip feed line, radiating structure, resonant frequency

I. INTRODUCTION This nowadays wireless communications is rapid in

increasingly the technology development. The rapid progress promises to make interactive voice, data and video services available anytime and anyplace. Wireless communication systems come in variety of different sizes ranging from small hand-held devices to wireless local area networks [1]. The increasing in the use of the wireless portable devices and many others commercial applications in the wireless communications have increasing the demand of the services such as data or video transfer [2].

In the wireless systems there are lot types of antennas that have been developed for its commercial. As mention before, the higher demands of wireless portable devices have drag to the developing of dual band antennas which have multi applications and also can provide large bandwidth so that it can cover all operating frequencies needed in the system [2-5].

The designed antennas also need to satisfy the IEEE802.11 WLAN standards. The IEEE802.11 is the most famous protocol that has been used widely nowadays. This has led to the development of the antenna that can cover multiband applications and provide enough bandwidth to cover the operating frequencies within it. People found that wireless portable devices are very attractive because the user can use the devices without any cables and they also can move anywhere

as long as they in the coverage area. There is also a reason of developing a dual band antenna is to increase the bandwidth. The popularity of wireless communications has made the system need to be more specific regarding the capacities it can carry and also the speed of the transmission [6-9]. In the wireless communication today, the antenna design has facing many problems such as challenges to make a broadband antenna and now dual band antenna issues are arises. The proposed antenna is designed to overcome the dual band issues

II. ANTENNA DESIGN Previous work has been done on the novel compact printed

antenna with radiating structure of 2.5 for dual band applications at 2.4 GHz and 5.2/5.8 GHz [2]. This paper has proposed different radiating structure for same applications. The radiating structure that has been proposed in this paper is 3.5.

The basic structure for the 3.5 antenna consists of 3 layers which are patch, dielectric substrate and ground plane as shown in Fig. 1. The top layer is patch or antenna layer which is the radiator that made from the copper (annealed) with thickness of 0.035 mm. Then, the second layer is dielectric substrate (80 mm×80 mm). In this paper the material that has been used for dielectric substrate is FR4 board with thickness of 1.6 mm, dielectric constant of 4.4 and tangent loss of 0.019. While the bottom layer is the ground plane that used material from the copper annealed with thickness of 0.035 mm. The ground plane also consists of SMA connecter which used as RF connecter to connect the 50 Ω coaxial cable and the 50 Ω microstrip lines on a board. The proposed antenna was designed and simulated using CST Studio Suite software.

Lengths of the radiating structure 3 and 5 are based on the /4 [10-14]. The antenna geometry of radiating structure 3 and

5 are shown in Fig. 2. The feeding methods that have been used in this paper is coplanar waveguide feed line. The feed line is inserted at the radiating structure 5 to achieved dual band. The antenna dimensions are shown in Table I.

13th Conference on Microwave Techniques COMITE 2013, April 17-18, Pardubice, Czech Republic

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Figure 1. Basic antenna structure from side view

(a) (b)

Figure 2. Antenna geometry using microstrip technique (a) Structure 3

(b) Structure 5

TABLE I. THE DIMENSIONS OF THE 3.5 ANTENNA IN MM

Symbol Dimension L1 12.5

L2 5

L3 3.3

L4 3.5

L5 4.5

L6 16.67

L7 3

L8 7.5

L9 3

L10 2.39

LF 46.5

wf 1.913

The basic structure of 3 and 5 as in Fig. 3 is designed. Then, both structures 3 and 5 are combined to form 3.5-shaped antenna. A coplanar waveguide technique has been used to achieve dual band frequencies. The feeding method that has been used is coplanar waveguide feed. The radiating structure 3 is placed at the same plane with radiating structure 5. The radiating structure 3 and 5 are combined to achieve dual band frequencies. Both radiating structures are surrounding with slot.

The position of the radiating structure 3 is turned to 90° so that the antenna can achieved dual band frequencies at 2.4 GHz and 5.2 GHz. The prototype of the antenna is shown in Fig. 4.

(a)

(b)

Figure 3. Antenna structure using Coplanar Waveguide (CPW) technique (a) Front view (b) Back view

(a) (b)

Figure 4. Antenna Prototype using Coplanar Waveguide (CPW) technique (a) Front view (b) Back view

III. RESULTS AND ANALYSIS The results are obtained from the simulation and also

measurement process. The simulation is done by using CST studio suite software. The results from the simulations were then validated with experimental measurements of a prototype that has been fabricated.

A. Return Loss The simulation results shown the return loss for the 2.4

GHz is -16.443 dB while for 5.2 GHz is -19.964 dB where the return loss is less than -10 dB. Thus 90% of signal is transmitted to the receiver and only 10% of signal is reflected back to the transmitter from the receiver.

B. Bandwidth The bandwidth for 2.4 GHz is 1259.3 MHz and 5.2 GHz is

1191.4 MHz. The bandwidth is met the design specification which is required more than 200 MHz which can cover the applications that needed for the antenna.

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C. Gain and Directivity The gain for 2.4 GHz is 4.697 dB and for 5.2 GHz is 5.683

dB. These results are shown good agreement to the design specification which is more than 3 dB for 2.4 GHz and 5.2 GHz. The directivity for 2.4 GHz is 5.335 dBi and for 5.2 GHz is 6.529 dBi.

D. Radiation Efficiency While the radiation efficiency for 2.4 GHz is -0.6382 dB

and for 5.2 GHz is -0.8466 dB which is more than 50% efficiency where the antenna able to receives more than 50% of power transmitted.

E. Surface Current and Radiation Pattern The surface current at 2.4 GHz is less radiated at the

radiating structure 5 and 3 while surface current at 5.2 GHz is radiated more at radiating structure 3 and 5. At 5.2 GHz the current is more at radiating structure 3 and 5. Currents are more radiated at feed line for both frequencies. Fig. 5 and Fig. 6 are shown the surface current and radiation pattern for the proposed antenna.

(a)

(b)

Figure 5. Surface current at the (a) 2.4 GHz (b) 5.2 GHz

(a)

(b)

Figure 6. Radiation pattern at the 2.4 GHz and 5.2 GHz (a) = 90 ° (b) 0 °

F. Radiation Comparison between simulation and measurement results Most of the measurement results are agreed with the

simulation results but there are still a few different between simulation and measurement results. This is due to the environmental effect when the measurement process and fabrication process that need to take into account. The measurement result of the proposed antenna is shown in the Fig. 7. Table 2 is shown the comparison between simulation and measurement results of the proposed antenna. Fig. 8 is shown the comparison of the return loss of the simulation and measurement of the proposed antenna.

TABLE II. COMPARISON BETWEEN SIMULATION AND MEASUREMENT RESULTS

Frequency (GHz)

2.4 5.2 Simulation Measurement Simulation Measurement

Return Loss (dB)

-16.443 -23.213 -19.964 -18.702

Bandwidth (MHz)

1259.3 1006.2 1191.4 1067.9

Gain (dB) 4.697 2.749 5.683 3.299

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Figure 7. The measurement result of the proposed antenna

Figure 8. Comparison between the return loss of the simulation and measurement of the proposed antenna

IV. DISCUSSION Few parametric studies have been done on length feed, LF and width slot, s1 as shown in Fig. 9. When the length feed, LF is increasing, the upper frequency and the lower frequency are shifted. The bandwidth for the upper frequency is decreasing as the LF is increasing as shown in Fig. 10. When the LF is increasing, the gains for lower and upper frequency are also increase. The directivity for lower and upper frequencies is decreasing as the LF is increasing.

Figure 9. Comparison between the return loss of the simulation and measurement of the proposed antenna

Figure 10. Graph return loss when length feed is vary When the width of slot, s1 is increasing, lower frequency is shifted. The return loss for the upper frequency is increasing when the s1 is increasing shown in Fig. 11. When the s1 is increasing, the directivity of the upper frequency is decreasing while the directivity of the upper frequency is increasing. As the s1 is increasing, the gain at the lower frequency is decreasing while the gain at the upper frequency is increasing.

Figure 11. Graph return loss when width of slot is vary when length of feed,

LF = 48.6mm

V. CONCLUSION The 3.5 slot antenna by using Coplanar Waveguide (CPW)

technique is proposed in this paper. The return loss for both resonant frequencies are less than -10 dB where 90% of the input signal is transmitted and only 10% of the input signal is reflected back. The bandwidth is wider enough to cover the operating frequencies for the application needed. The proposed antenna can operate at dual band frequencies which can cover more than one application in one system with wider bandwidth, higher gain and good radiation efficiency.

ACKNOWLEDGMENT The authors thank to UTeM for their support in obtaining

the information used and material in development work, and we thank the anonymous referees whose comments led to an improved presentation of our work.

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