4A5_1438

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1438 PIERS Proceedings, Beijing, China, March 23–27, 2009

Microstrip Slot Antenna with a Finite Ground Plane for

3.1–10.6 GHz Ultra Wideband Communication

Huan-Cheng Lien1, Yung-Cheng Lee1, Wen-Fei Lee2, and Huei-Chiou Tsai2

1Department of Security Management, WuFeng Institute of Technology, Taiwan2Department of Electrical Engineering, WuFeng Institute of Technology, Taiwan

Abstract— This paper introduces an Ultra Wideband microstrip Slot Antenna conformed tocraving for the band of IEEE802.15.3a UWB (3.1GHz ∼ 10.6 GHz) communication. In thispaper, the design for enhancing impedance bandwidth of wideband microstrip slotting antennawith a finite ground plane is proposed and studied. With this design, a matching impedancebandwidth (SWR ≤ 2) about of more than 146% was achieved; as a result, the bandwidth canbe located at the wireless communications from 2.3 GHz to 12 GHz. The variations of gain arechanging from 0.2 to 6.98 dBi. In addition, the design has been a planar profile and it can easilybe integrated in small mobile units; besides, it also can be in the laptops or various remote-sensingdevices etc..

1. INTRODUCTION

In the communication systems, to develop small size, lightweight, low profile, broad bandwidth, andproper polarization are fundamental demands in the antenna design for the miniaturization of thecommunication equipment. Microstrip antennas have many desirable features, such as low profile,lightweight, and are usually fabricated by a photolithographic etching process or a mechanicalmilling process of these kinds antennas, making the construction relatively easy and inexpensive.These features make microstrip antennas are one of the most widely used types of antennas inthe microwave frequency range, and they are often useful for many applications in the satellitecommunication and mobile communication systems. However, the ma jor drawback of these kindsof antennas inherently has limited impedance bandwidth (VSWR? 2), if the narrow bandwidthof the microstrip antenna can be widened, then it can serve as a dual antenna for second- andthird-generations of mobile communications systems. Therefore, developing broadband techniques

to enhance the bandwidths of the microstrip antennas is very important.Recently, most of the research on microstrip antennas focused on methods to increase theirbandwidth. Slot antennas exhibit wider bandwidth, lower dispersion and lower radiation loss thanmicrostrip antennas, and when feeding by a coplanar waveguide they also provide an easy means of the parallel and series connection of active and passive elements that are required for improving theimpedance matching and gain [1]. The U-slot antenna, which achieves a relatively broad bandwidthwithout a parasitic patch, has been reported [2]. A lot of slot antennas for enhancing impedancebandwidth have been investigated [3–5].

A broader bandwidth, obtained using an improved feeding method, has also been reported [6].It is very important to choose a suitable feeding circuit since it controls the antenna performance interms of bandwidth. A bandwidth of 10 GHz ultra wide bands square planar metal-plate monopoleantennas has been proposed propos ing in a 3D geometric configuration [7]. However, this 3Dgeometry designs needs more space, which is not suitable for mobile terminals, where the space is

very limited.The recent allocation of the 3.1–10.6 GHz frequency spectrums by the Federal Communications

Commission (FCC) for Ultra Wideband (UWB) radio applications has had presented challenges forthe antenna designers. For many UWB wireless communications, the successful transmission andreception of UWB pulses, sufficient impedance matching, the characteristics of the antenna withomni directional radiation pattern, high radiation efficiency, and easy manufacturing are required.

In this paper, a novel design of microstrip slot antenna with a finite ground plane for the desiredband of IEEE802.15.3a UWB (3.1GHz ∼ 10.6 GHz) is studied. This design of the proposed antennais different from that of the other slot antennas with a tuning stub to enhance impedance band-width [8–12], and successfully implemented and the simulated results show reasonable agreementwith the measured results. From experimental results, the proposed antenna shows that geome-tries can a significant increase in the impedance bandwidth obviously and, with respect to 10-dBimpedance, the widest band obtained was 95%. Radiation patterns and gains are also examined.

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2. DESIGN AND REALIZATION

The configuration of the ultra wideband microstrip slot patch antenna is shown in Fig. 1. Theantenna has compact dimensions of 30.5× 35.3 mm2, which consists of wide-slot ground plane withthe same four small corners, fork-like U-type radiating element, a 50 O microstrip feed line, a smallparasitical ground plane and a finite ground plane. Where the fork-like U-type radiating elementand the 50 O microstrip feed line is coplanar with place in the back of the wide-slot ground plane,and printed on the substrate FR4 of thickness 1.6 mm and relative permittivity 4.4.

X

t

hFeed line

SMA connector

Small parasitical ground plane

U-type radiator

Wide-slot ground plane

Z

(b) Cross section(a) Wide-slot ground plane

2W

1W

1 L 2 L

Z

X

a b×

Figure 1: Configurations of the ultra wideband microstrip slot antenna with a small parasitical ground plane.

The internal and external wide-slot ground plane has dimensions of L1 (L’ 2) wide, W 1 (W ’ 2)long, respectively. The dimension of the small corner is Xa by Y b. The fork-like U-type radiatingelement is divided into three parts., These dimensions are 1 by w1, 2 by w2, and 3 by w3,respectively. The small parasitical ground plane finite ground plane has dimensions of x wide ylong, and the thickness of d, that is suspended at h mm under the fork-like U-type radiating element,and connected to the 50 ohms SMA connector. By properly adjusting the dimensions of the smallparasitical ground plane finite ground plane, the radiator element, and the spacing h of betweenthe small parasitical finite ground planes relative to the radiating element, a better impedancematching can be achieved. The design optimized parameters of all the components are listed in the

Table 1. A photograph of the fabricated rectangular patch antenna is shown in Fig. 2.

Table 1: The relative parameters of the proposed antenna (Unit: mm).

1 U-type radiating element c = 0.9, d = 10, e = 10.4, f = 1.1

2 Rectangular microstrip feed line 3 × 4.12

3 Wide-slot ground plane L2 = 23.9, W 2 = 30.5

L1 = 35.3, W 1 = 42.8

4 small parasitical ground plane x = 16, y = 8, thickness = 0.35

5 SMA connector 50 ohm

6 small corner a = 2.5, b = 3.2

FR4 Dielectric substrate εr1 = 4.4, tan δ = 0.022RO Dielectric substrate εr2 = 3.38, tan δ = 0.0025

3. MEASUREMENTS AND DISCUSSION

The design was also analyzed using Zeland Software’s IE3D simulation package. According tothe above-mentioned design optimized parameters of all the components are listed in the Table 1,the performance of impedance bandwidth is improved for y is between 8 mm ∼ 9 mm. Using anHP8720D vector network analyzer, the return loss curves of both simulated and measured withthe finite ground plane proposed antenna is obtained at 2 ∼ 12 GHz, as depicted in Fig. 3. Thecomparison between the measurements and software predictions are very close. The differencebetween the two graphs is also due to the fact that the proposed antenna was built on a finite

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1440 PIERS Proceedings, Beijing, China, March 23–27, 2009

Top view

X

Y

Z

U-type radiator c d

e f ×

×

Figure 2: Configuration top view of the widebandslot antenna with a small parasitical ground plane.

Figure 3: Measured and simulated return loss forthe proposed antenna.

finite ground plane (102 mm× 76.2 mm) and the parasitical ground plane, while the computationsassume an infinite ground plane. For the 10 dB return loss, the measured maximum impedancebandwidth of the proposed antenna is from 2.3 GHz to 12 GHz, corresponding to an impedancebandwidth of 136.6 percent centered at on 7.1 GHz. Here, the impact of the finite finite groundplane is more pronounced. Therefore, the proposed antenna has good impedance bandwidth forthe band of IEEE802.15.3a.

The radiation patterns of the proposed antennas with a finite ground plane are measured. Fig. 4plot the measured radiation E -plane patterns patterned at on 3.1 GHz for the proposed antenna.From the measured test results, the finite ground plane does not dominate the radiation powerpatterns. Fig. 5 shows the measured gain versus the frequency. Within the operating frequency

band, the gain of the proposed antenna is 0.04dBi to 6.98dBi for the antenna with finite groundplane.

Figure 4: The experimental E -plane patterns of pro-posed antenna.

Frequency (GHz)

dBi

Figure 5: Measured and simulated gains versus fre-quency.

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4. CONCLUSIONS

A new ultra-wideband antenna has been proposed for UWB applications. This The proposedantenna is uses employing a fork-like U-type radiating element structure with a finite groundplane and wide-slot ground plane for bandwidth enhancement. The simulated results conductedby the Zeland Software’s IE3D simulation package show reasonable agreement with the measuredresults. The obtained results show an impedance bandwidth of more than 137% covering the wholeIEEE802.15.3a defined UWB frequency band. Acceptable radiation characteristics at on the 3.1,5.1, and 10.6 GHz, and the measureding antenna gain is 0.04dBi to 6.98dBi cover the 2 ∼ 12 GHzoperation frequency ranges that makes this class of antennas a good candidate for a variety of thecommunication applications. Except for the enhancement of impedance bandwidth, the effects of the ground plane to the power patterns and peak gain value are small.

REFERENCES

1. Wong, K.-L., Compact and Broadband Microstrip Antennas , John Wiley and Sons Inc., NewYork, NY, 2002.

2. Lee, K. F., et al., “Experimental and simulation studies of the coaxially fed U-slot rectangularpatch antenna,” IEE Proceedings — Microwave Antennas and Propagation , Vol. 144, No. 5,354–358, 1997.

3. Kahrizi, M., T. K. Sarkar, and Z. A. Maricevic, “Analysis of a wide radiating slot in ground

plane of a microstrip line,” IEEE Trans. Microwave Theory Tech., Vol. 41, 29–37, Jan. 1993.4. Tong, K.-F., K.-M. Luk, K.-F. Lee, and R. Q. Lee, “A broad-band U-slot rectangular patchantenna on a microwave substrate,” IEEE Trans. Antennas Propagat., Vol. 48, 954–960,Jun. 2000.

5. Chen, H.-D., “Compact circularly polarized microstrip antenna with slotted ground plane,”Electron. Lett., Vol. 38, Jun. 20, 2002.

6. Mak, C. L., K. M. Luk, and K. F. Lee, “Microstrip line-fed L-strip patch antenna,” IEE Proceedings — Microwave Antennas and Propagation , Vol. 146, No. 4, 282–284, 1999.

7. Wong, K.-L., C. H. Wu, and S. W. (Stephen) Su, “Ultra wide-band square metal-platemonopole antenna with a trident-shaped feeding strip,” IEEE Trans. Antennas Propagat.,Vol. 53, No. 4, 1262–1269, Apr. 2005.

8. Lin, X.-C. and L.-T. Wang, “A broadband CPW-fed loop slot antenna with harmonic control,”Antennas and Wireless Propagation Letters , Vol. 2, 323–325, 2003.

9. Chen, H.-D., “Broadband CPW-fed square slot antennas with a widened tuning stub,” IEEE Trans. Antennas Propagat., Vol. 51, 1982–1986, Aug. 2003.

10. Leung, K. W. and C. K. Leung, “Wideband dielectric resonator antenna excited by cavity-backed circular aperture with microstrip-line tuning fork,” Electron. Lett., Vol. 39, 1033–1035,Jul. 10, 2003.

11. Sze, J.-Y. and K.-L. Wong, “Bandwidth enhancement of a microstrip-line-fed printed wide-wide-slot antenna,” IEEE Trans. Antennas Propagat., Vol. 49, 1020–1024, Jul. 2001.

12. Chiou, J.-Y., J.-Y. Sze, and K.-L. Wong, “A broad-band CPW-fed strip-loaded square slotantenna,” IEEE Trans. Antennas Propagat., Vol. 51, 719–721, Apr. 2003.

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