Designing Dual-band Antenna for WiMAX

Nguyen Van Trinh College of Technology Viet Nam National University,

Ha Noi, Viet Nam. E-mail: regret.dtvt@gmail.com

Tran Minh Tuan National Institute of Information and Communications

Strategy, Viet Nam E-mail: tm_tuan@mic.gov.vn

Abstract—This paper concentrates on studying, designing and manufacturing a dualband microstrip antenna, that is able to operate within 2.5 – 2.69 GHz (2.5 GHz band ) and 3.4 – 3.6 GHz (3.5 GHz band). Antenna is made from FR4-epoxy substrate having ε = 4.4, h= 1.6 mm (thickness). It has folder structure and includes three branches: two resonant branches and tuning branch which are fed by 50 Ω microstrip line.

Keywords-component; WiMAX; antenna; dual-band; microstip antenna.

I. INTRODUCTION In recent years, the wireless communication has been

developed very rapidly, especially WiMAX technology.

Worldwide Interoperability for Microwave Access (WiMAX) is currently one of the emerged wireless technologies. The Institute of Electrical and Electronics Engineers (IEEE) 802 committee, which sets networking standards that define WiMAX IEEE 802.16-2004 (also known as Revision D) was published in 2004 for fixed application; 802.16 Revision E (which adds mobility) is publicized in July 2005.

The WiMAX Forum has adopted certain profiles based on the 802.16 standards operating in the 0.7 – 0.8 GHz, 2.3 GHz (2.3 – 2.4 GHz), 2.5 GHz (2.5 – 2.69 GHz), 3.3 GHz (3.3 – 3.4 GHz), 3.5 GHz (3.4 - 3.6 GHz), 3.6 - 3.8 GHz and 5.8 GHz (5.725 – 5.850 GHz) frequency bands. WiMAX can be used for a number of applications, including “last mile” broadband connections, hotspots and high-speed connectivity for business customer. It provides wireless metropolitan area network (MAN) connectivity at speeds up to 70 Mbps and the WiMAX base station on the average can over between from 5 to 10 km [1].

Recently, two frequency bands (2.5 GHz and 3.5 GHz) are most preferable, but design of an antenna working simultaneously in these frequency bands is costly and complicated. This paper concentrates in designing and manufacturing of planar monopole microstrip antenna with 2D structure working in 2.5 GHz and 3.5 GHz frequency bands. By selecting an antenna structure and carefully adjusting the parameters, we can achieve multi-resonant and broadband properties [2], which are able to satisfy designing demands of applications in WiMAX network.

II. DESIGN ANTENNA AND SIMULATION RESULTS

Figure 1. Overview of the antenna

The planar monopole antenna includes two resonant branches and a tuning branch. Antenna is printed on a FR4 - epoxy substrate and is fed by a 50 Ohm microstrip line. This antenna can be used for WiMAX within 2.5 GHz, 3.5 GHz bands, with VSWR Belows 2.5.

An overview of this antenna is as in Fig. 1. The antenna surface area is 80 mm x 45 mm. The antenna structure includes two parts: radiator and 50 Ohm microstrip line. On the other surface, ground plane (GND) is printed with an area of 45 mm x 45 mm.

The length of 50 Ohm microstrip line is about 47 mm and the width is about 3 mm.

The radiator includes two resonant branches and a tuning branch.

The length of the first resonant branch from feeding point to its end is about 30 mm. This value is approximate to ¼ of the wavelength at the 2.5 GHz in the free space. The width of the first resonant branch is about 3 mm. It should be noted that resonant frequency depends on both the length and the width of the end.

In the same way, the length of the second resonant branch from feeding point to its end is about 21.5 mm, approximately

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to ¼ of the wavelength at 3.5 GHz in the free space. The width of the second resonant branch is about 3 mm.

The tuning branch is added to reach demanded bandwidth. The width of tuning branch is designed to be 3 mm length. By carefully tuning the length of the tuning branch, the bandwidths of two resonant frequencies (2.5 GHz and 3.5 GHz) are increased significantly. In this case, we adjusted the length of tuning branch is 23 mm as in Fig. 1.

Impedance matching is performed by two resonant branches and tuning branch.

Figure 2. Return Loss (dB)

The simulation carried out by Ansoft HFSS 11.0 software. Fig. 2 shows the result for Return Loss of antenna.

With Return Loss = -30 dB (similar to VSWR = 1.0634) at 2.5 GHz, and Return Loss = -20 dB (similar to VSWR = 1.212) at 3.5 GHz. We can see that antenna with the tuning branch have bandwidth from 2.25 GHz to 2.75 GHz (about 500 MHz) at 2.5 GHz frequency band and from 3.2 GHz to 3.85 GHz (about 650 MHz) at 3.5 GHz frequency band.

Belows are bandwidth as set of 802.16 standard and bandwidth as in simulation

TABLE I. BANDWITH OF 802.16 STANDARD

Bands Frequency Bandwidth

2.3 GHz 2.3 – 2.4 GHz 100 MHz 2.5 GHz 2.5 - 2.69 GHz 169 MHz 3.3 GHz 3.3 – 3.4 GHz 100 MHz 3.5 GHz 3.4 – 3.6 GHz 200 MHz

3.6 – 3.8 GHz 3.6 – 3.8 GHz 200 MHz

TABLE II. THE RESULT OF THE SIMULATION

Bands Resonant frequency Bandwidth VSWR = 1.92

2.5 GHz 2.5 GHz 2.25 – 2.75 GHz 3.5 GHz 3.5 GHZ 3.2 - 3.85 GHz

From TABLE I and TABLE II, we can see that this antenna not only covers almost 2.5 GHz and 3.5 GHz bands but also can cover 2.3 GHz, 3.3 GHz and 3.6 – 3.8 GHz bands.

Therefore, the antenna in this paper can cover five bands: 2.3 GHz, 2.5 GHz, 3.3 GHz, 3.5 GHz, and 3.6 - 3.8 GHz bands. Beside, this antenna can be used in RFID at 2.45 GHz band and in WIFI at 2.4 GHz band.

Radiation patterns in XOY, XOZ and YOZ planes (Fig. 3) bellows:

(a) XOY plane

(b) XOZ plane

(c) YOZ plane

Figure 3. Radiation patterns in 2D

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From Fig. 3, we can see that at 2.5 GHz, this antenna almost radiates isotropy in XOY plane, and direction in XOY, YOZ plane. At 3.5 GHz, this antenna almost radiates isotropy in YOZ plane, and direction in XOY, XOZ plane.

Belows are radiation pattern in 3D (Fig. 4).

(a) Radiation pattern at 2.5 GHz

(b) Radiation pattern at 3.5 GHz

Figure 4. Radiation pattern in 3D

From Fig. 4, we can see that when frequency is increased, radiation pattern of antenna is distorted gradually. The reason of this problem is the impact of ground’s radiation, the impact of microstrip line and impedance deviation…

III. MEASUREMENT RESULT Fig. 4 shows measurement result for Return Loss. Return

Loss is displayed by Network Analyzer.

Figure 5. Measurement result

With Return Loss = -10 dB, VSWR equal to 1.92, bandwidth from Network Analyzer for respective bands are as follows:

TABLE III. BANDWIDTH AS MEASUREMENT

Bands Frequency range Bandwidth VSWR = 1.92

2.5 GHz 2.363 – 2.645 GHz 282 MHz 3.5 GHz 3.420 – 3.582 GHz 162 MHz

From TABLE III. BANDWIDTH AS MEASUREMENT, we can see that bandwidth of this antenna can only cover a part 2.3 GHz band (2.363 - 2.4 GHz equal to 37 MHz bandwidth) and almost cover 2.5 GHz band (2.5 – 2.645 GHz equal to 145 MHz bandwidth). This antenna can almost cover 3.5 GHz band (3.420 – 3.582 GHz equal to 162 MHz bandwidth). But the antenna can not cover 3.3 GHz and 3.6 – 3.8 GHz bands as in simulation result. Beside, from the result of measurement, we see that this antenna can use in RFID at 2.45 GHz band and in WIFI at 2.4 GHz band as well.

Belows graph shows measurement and simulation result.

Figure 6. The comparision between the measurement and simulation result

The measurement result and simulation result quite agree to each other. However the achieved bandwidth has not

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completely covered all five demanded bands, especially the 3.3 GHz and 3.6 – 3.8 GHz band as in simulation.

The real shape of antenna is shown in Fig. 7

(a) Top view

(b) Bottom view

Figure 7. The real shape of the antenna

IV. CONSULION The designed antenna is well designed and can completely

apply for WiMAX within 2.5 GHz, 3.5 GHz bands and a part 2.3 GHz band. Beside, this antenna can apply for RFID and WIFI within 2.45 GHz and 2.4 GHz band. However, the measurement result is not good as simulation one and therefore, we need to adjust further some parameters of the antenna so that it’s bandwidth can cover all 3.3 GHz, 3.6 – 3.8 GHz and 2.3 GHz bands

REFERENCES

[1] Sanida Omerovic, “WiMax Overview,” Faculty of Electrical

Engineering, University of Ljubljana, Slovenia. [2] Girish Kumar and K.P. Ray, “Broadband Microstrip Antennas,” Artech

House antennas and propaggation library. [3] Prof. Phan Anh, “Antenna Theory and Technique”, Science and

Technical Press, Hanoi 2000.

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