a wideband rectangular-slot microstrip array antenna...

A Wideband Rectangular-slot Microstrip Array

Antenna for Wireless Applications

Obeng Kwakye Kingsford Sarkodie

Abstract—This paper presents the design of a 2 x 2 microstrip

array antenna suitable for wireless applications. The proposed

antenna comprises of 4 rectangular patches where diagonal patches

have the same length and width. A larger bandwidth and the desired

resonant frequency are achieved because of a reduction in the quality

factor (Q) of the patch resonator, which is due to less energy being

stored beneath the patch due to the rectangular arrangement of the

slots. The characterization results of return loss, gain, and radiation

pattern are presented consecutively. From the results, the simulated

impedance bandwidth defined for S11<-10dB reaches 1850MHz

(4.69-6.54GHz) representing 16.47%.

Keywords— wideband, array antenna, slot, patch, wireless

I. INTRODUCTION

ICROSTRIP antennas have been popular for decades

because they exhibit a low profile, small size,

lightweight, low manufacturing cost, high efficiency,

and an easy method of fabrication and installation.

Furthermore, they are generally economical to produce since

they are readily adaptable to hybrid and monolithic integrated

circuits fabrication techniques at radio frequency (RF) and

microwave frequencies [1]. One of the most important

disadvantages of microstrip patch antenna is their narrow

bandwidth. To overcome this problem and for the antenna to

work within a stipulated band, a number of methods and

structures have recently been proposed. Mention can be made

of wideband aperture coupled microstrip array antennas [2],

U-slot with proposed π-shaped stub [3], double rectangular

patch with bridges [4], stacked layered structures [5],

resonator antennas with capacitive coupled parasitic patch

element [6], circular edge truncation [7].

This paper presents a wideband 2 x 2 rectangular slot

microstrip antenna which covers the WLAN band. WLAN

takes advantage of license free frequency bands, industrial,

scientific, medical (ISM) bands and uses one of frequency

band 5.15 to 5.825 GHz (IEEE 802.11a) [8]. Since WiMAX

has three allocated frequency bands called low band (2.5 GHz

to 2.8 GHz), middle band (3.2 GHz to 3.8 GHz), and high

band (5.2 GHz to 5.8 GHz), the proposed antenna is also

applicable to WiMAX. The impedance bandwidth in

percentage is 16.47% which is far higher than that of [4] who

compared double rectangular patch with 4 bridges for 2.4GHz

and 5.5GHz WLAN applications.

Obeng Kwakye Kingsford Sarkodie is a PhD Student at the University of

Electronic Science and Technology of China, China, Chengdu, Sichuan.

(Email: [email protected])

It also has a higher bandwidth than [8] and [9] who recorded 14% for WiMAX and 14.1% for WLAN applications respectively.

II. ANTENNA CONFIGURATION

Fig. 1 depicts the structure of the 2 x 2 rectangular slot

microstrip array antenna which comprises of three layers,

including top, middle, and bottom layers. The radiating

elements are on the top layer, the middle layer is a metal

ground with rectangular slots and the bottom layer consists of

a microstrip feed line. The bottom layer is between the feed

line and the metal ground. The top layer is between the

radiating element and metal ground.

Fig. 1 Configuration of the 2 x 2 microstrip array antenna elements

In this design, a material with a permittivity Єr2=2.2 and

Єr1=1 are chosen as the top and bottom materials respectively,

with same height of 0.8mm. It is noted that the sizes of all

substrates and the ground plane are the same (50x50mm2). The

radiating elements A has a size of 7.5x11mm2 whiles that of B

has a size of 9x11mm2 as shown in Fig. 1. The arrangement of

the slots on the ground plane accounts for the double

frequency resonance, that’s 5.23GHz and 6.31GHz. The

spaces between the radiating elements are set at 20mm for

better radiating characteristics. The rectangular arrangement of

the slots in the ground plane has a size of 3x7mm2 and spaced

10mm apart. To obtain the desired radiation pattern with its

associated characteristics, a 2x2 planar microstrip slot array

antenna is designed. The bottom substrate consists of the

microstrip feeding network which is designed to give equal

amplitude and phase to each element where it is matched to a

50 ohms feed line.

M

2nd Intl' Conference on Advances in Engineering Sciences and Applied Mathematics (ICAESAM’2014) May 4-5, 2014 Istanbul (Turkey)

http://dx.doi.org/10.15242/IIE.E0514063 80

III. RESULTS

The array antenna is simulated using the commercial Ansoft

HFSS design software. Fig. 2 shows the simulated return loss

of the proposed antenna. The simulated impedance bandwidth

defined for S11<-10 (VSWR) reaches 1850MHz (4.69-

6.54GHz) which covers the 5.15-5.95GHz WLAN and

WiMAX bands. There is a double frequency resonance which

is primarily due to the arrangement of the slots on the ground

plane. Fig. 3 shows the radiation patterns for Phi, Theta =

0degrees and Phi, Theta = 90degrees at both resonant

frequencies (5.23GHz and 6.31GHz). We can also find from

Fig. 3(a) and (b) that the half-power beam width (HPBW) is

60o in both E and H planes at 5.23GHz, in Fig 3(c), HPBW is

60o in the E plane and 62o in the H planes. Similarly, in Fig.

3(d) HPBW is 60o in the E plane and 58o in the H plane.

Fig. 2 Return of the 2x2 array antenna

(a)

(b)

(c)

(d)

Fig. 3 Antenna pattern, E-plane is the solid blue line while H-plane is

the dotted red line (a) 5.23GHz, Phi, Theta = 0degrees (b) 5.23GHz,

Phi, Theta = 90degrees (c) 6.31GHz Phi, Theta = 0degrees (d)

6.31GHz, Phi, Theta = 90degrees

IV. OPTIMIZATION

Since radiating element is the basis of antenna array and its

form determines the realization and electrical performance of

antenna array, it is necessary to investigate the influence on

the element antenna due to the structure parameters.

Optimization about the size of the patch is showed in Fig.

4(a), 4(b), 4(c) and 4(d). As the width of patch A is varied, the

6.31GHz resonance decreased considerably, increasing that of

the 5.23GHz resonance to more than -50dB. When the length

of the patches takes a small change, it will have great

influence on the resonant frequency. So the effects on resonant

frequency due to the length of the patch should be paid

attention to. Different resonant resistances of the patch

antenna can be realized through the variation of width of the

patch. Optimization about the size of the slot is shown in Fig

4(e) and 4(f). The resonant frequency decreases when the

length of the slot of reduced and changes when the length is

increased. Meanwhile the resonant resistance increases

significantly and the coupling strength increases. The length of

the slot cannot be set too long, or it will enhance the backward

radiation. But if the length of the slot is too short, it cannot

ensure enough coupling. The width of the slot has the same

performance as well as the length. But the width usually is

limited below a very small value for decreasing the backward

radiation. So the length rather than the width is adjusted in the

design process. Fig. 4(g) shows the return loss when the slots

are removed. It can clearly be seen that the slots plays an

important role in widening the bandwidth.



(a)

(b)

(c)

(d)

(e)

(f)

(g)

Fig. 4 Parameter Optmization (a). about width of patch B (b). about

length of patch B (c). about width of patch A (d). about length of

patch A (e). about length of slot (f). about width of slot (g) about

without slot

V. CONCLUSION

A rectangular slot 2 x 2 microstrip array antenna has been

proposed where the simulated impedance bandwidth defined

for S11<-10dB (VSWR) reaches 1850MHz (4.69-6.54GHz)

representing 16.47% has been achieved. The proposed antenna

can be used for wireless applications such as WLAN and

WiMAX.

VI. REFERENCES

[1] L. G. Maloratsky, “Reviewing the basics of microstrip lines,” Microwave & RF. pp. 79-88, March 2000.

[2] Mohanna, S,; Ghassemi, N., “Wideband aperture coupled microstrip array antennas for radar applications,” Microwave Radar and Wireless Communications(MIKON), 2010 18th International Conference on Radar and Wireless Communications. pp. 1-2, June 2010

[3] K.L.Lau, K.M.Luk and K.F.Lee, ”Wideband U-slot microstrip patch antenna array,” IEE Proc.-Microw. Antennas Propag., Vol. 148, No. 1. pp. 41- 44 February 2001.

http://dx.doi.org/10.1049/ip-map:20010220

[4] Chang won Jung and Franco De Flaviis, “A Dual-Band Antenna for WLAN Applications by Double Rectangular Patch with 4-Bridges,” Antennas and Propagation Society International Symposium, 2004. IEEE, vol. 4, pp 4280 – 4283, June 2004

[5] S. Egashira, E. Nishiyama, A. Sakitani, “Stacked microstrip antenna with wide band and high gain,” IEEE Antennas and Propagation Society International Symposium, vol. 3, pp. 1132-1135, May 1990.

[6] Pues H.F. and Van De Capelle A.R. “Impedance matching of microstrip resonator antenna,” Proceedings of the North American Radio Science Meeting, Quebec, pp. 189, 1980.

[7] Swapnil S. Thorat, R.C. Jaiswal, Dr. Rajkumar, S.D. Lokhande, “Efficient technique for Bandwidth Improvement of Microstrip Patch Antenna,” International Journal of Computer Networks and Wireless Communications(IJCNWC), Vol. 2, No6, pp. 728-732, Dec 2012







[8] Amir Reza Dastkhosh and Hamid Raza Dalili Oskouei, “A wideband High-Gain Dual-Polarized Slot Array Patch Antenna for WiMAX Applications in 5.8GHz, “International Journal of Antennas and Propagation, vol. 2012, Article ID 595290, 6pages 2012.

[9] Chao Sun; Jiu-sheng Li, “A novel planar microstrip array antenna for WLAN applications,” Microwave, Antenna, Propagation, and EMC Technologies for Wireless Communications (MAPE), pp. 16-17, Nov 2011

Obeng Kwaye Kingsford

Sarkodie (S’14) was born in Kumasi, Ghana in 1986. He received the B.S degree from the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in 2009. He received the M.S degree from the University of Electronic Science and Technoly of China in 2012, where he is currently working toward the PhD degree. Prior to his continuing education at the University of Electronic Science and Technolgy of China, he was a

teaching assistant at the Kwame Nkrumah University of Science and Technolgy, Kumasi, Ghana.

His research interests includes electromagnetic fields in layered media, Sommerfeld integrals and microstrip array antennas.



a wideband rectangular-slot microstrip array antenna...

Documents