SMALL UWB PRINTED ANTENNA WITH SLOTTED GROUND PLANE

Rozanah Amir Khan, Chandan Kumar Chakrabarty and Lee Chia Ping Center for Communication Service Convergence Technologies Department of Electronics and Communication Engineering

Universiti Tenaga Nasional Kajang, Malaysia

rozanah@uniten.edu.my, chandan@uniten.edu.my, cp.lee87@yahoo.com.

Abstract-This paper presents an optimization design for the rectangular printed antenna with a slot ground plane for ultra wideband (UWB) application. A slot in the ground plane is shown to improve the bandwidth. The proposed antenna has a small size of 15 x 14.5 mm². The design is on FR-4 substrate with dielectric constant of 4.4 and thickness 1.6 mm. Simulation is performed by using the CST Microwave Studio software.

Keywords: Partial ground plane, printed ultra- wideband antenna, ground plane slot.

I. INTRODUCTION

The commercial use of frequency bands from 3.1 to 10.6 GHz was approved for ultra-wideband (UWB) systems by the Federal Communications Commission (FCC) in 2002 [1]. With the development of the high data rate wireless communication systems, there is always an increasing demand for smaller antenna size, greater capacities and transmission speeds, which certainly require more operating bandwidth [2-3].

Due to the attractive features, such as low profile, low cost, small size, radiation properties and ease of fabrication, the printed ultra-wideband antenna has received more and more attention with the advancement of communication technology [3-4]. However, a major disadvantage is their narrow bandwidth. For this reason, several techniques have been used to improve the impedance bandwidth of the printed antenna. These include the use of beveling technique, cutting notch, ground plane shaping and etc [3]. Bandwidth is affected very much by the size of the ground plane. By varying the size of the ground plane and introducing rectangular slot in the ground plane, the bandwidth of the printed antenna can be adjusted.

In this paper, the effect of varying the ground plane size and introducing a rectangular slot onto

the ground plane to improve bandwidth is shown. The design uses only simulation using the CST Microwave Studio software.

II. ANTENNA GEOMETRY

(a)

(b)

Wp

Lp

Ls

Wg

Lg

Ws

SL1SL2

Fw SW1 SW2

Proceedings of the 2009 IEEE 9th Malaysia International Conference on Communications 15 -17 December 2009 Kuala Lumpur Malaysia

978-1-4244-5532-4/09/$26.00 ©2009 IEEE 46

(c)

Figure 1. Antenna Configuration (a) Top (b) Bottom (c) Slot

The configuration of the proposed UWB antenna is illustrated in Figure 1. The antenna consists of rectangular patch antenna with two steps, a single slot on the patch and a partial ground plane. The printed antenna structure, which has compact dimensions of 15 x 14.5 mm², is printed on one side of the FR4 substrate with thickness of 1.6 mm and having dielectric constant of 4.4 with the ground on the other side. The dimensions of the antenna structure are shown in Table 1.

Table 1. Dimensions of antenna structure

Basic configuration

Variable Dimension (mm)

Patch antenna

Wp 15.0

Lp 12.5

SL1 1.5

SW1 1.5

SL2 1

SW2 1.5

Fw 2.4

Slot SlotW 10.0

SlotL 1.0

Ground plane Ws 2.4

Ls 6

Wg 35

Lg 9

The feedline is approximately a half wavelength transmission line with a characteristics impedance of 50 ohms. The length of Lg and Wg and the rectangular slot of width Ws and length Ls are introduced. To improve the impedance matching performance of the rectangular printed antenna, the effect of the size of the ground plane and rectangular slot at the ground plane is introduced. The design was then simulated in CST Microwave Studio.

III. EFFECTS OF SLOT ON IMPEDANCE BANDWIDTH

The proposed antenna has a slot imprinted on the printed antenna. Figure 2 shows the comparison between slotted antennas with unslotted antennas. It is shown that the impedance bandwidth of the slotted printed antenna is much wider than the unslotted antenna. This is due to the increased inductance of the patch radiator [9]. The unslotted antenna operates in the frequency between 2 GHz - 10 GHz whereas the slotted antenna is in the range between 2 GHz-12 GHz. The unslotted antenna displays patch resonant frequencies at 2.8 GHz and 6.32 GHz as compared to 2.68 GHz and 6.84GHz for the slotted antenna. The lower frequency is almost similar for both antenna and the upper frequency is shifted downward and slightly to the right for the slotted antenna. Therefore, the antenna with slot exhibits a better return loss value than the one without slot. Note that the slotted antenna introduces another resonant frequency at 8.94 GHz. Thus, the bandwidth broadening for the slotted antenna is due to the coupling of the patch antenna and slot.

SlotW

SlotL

47

Frequency (GHz)

Figure 2. Return loss characteristics for slotted and unslotted antenna.

IV. THE EFFECT OF GROUND PLANE SIZE ON IMPEDANCE BANDWIDTH.

The ground plane dimensions parameter plays an important role for designing an antenna due to its strong dependence of bandwidth on ground plane size [3].

Frequency (GHz) Figure 3. Return loss characteristics as a function

of Lg.

Figure 3 shows the return loss for different value of Lg. It is shown that the return loss at the lower-edge frequency increases with decreasing Lg for Lg = 7 mm, 8 mm and 9 mm. But for the Lg = 10 mm, the graph is shifted from 3 GHz to 4 GHz.

The return loss curves of frequency approximately at 7 GHz are getting worse as the Lg decreases for Lg = 7 mm , 8 mm, and 9 mm. The return loss at the higher-edge frequency decreases when Lg decreases for Lg = 7 mm, 8 mm and 9 mm except for Lg = 10 mm where it is shifted by 1 GHz. The bandwidth increases as the Lg increases. For Lg = 8 mm and 9 mm, it shows a good performance of ultra-wideband characteristics but for Lg = 10 mm the bandwidth is much wider. However for Lg =7 mm the bandwidth covered from 2 Ghz to 4 Ghz results in a narrow band characteristics where the return loss exceed – 10 dB.

Frequency (GHz)

Figure 4. Return loss characteristics as a function

of Wg.

Figure 4 shows the return loss for different value of Wg. The pattern of the graph shows similar impedance bandwidth which approximately covers the frequency range from 2 GHz to 11 GHz with respect to -10 dB. The return loss at the lower-edge frequency increases with increasing Wg for Wg = 25 mm, 30 mm and 35 mm. The return loss at the higher-edge frequency increases with decreasing Wg for Wg = 25 mm, 30 mm and 35 mm. Variation value of Wg in this graph exhibits good performance of ultra-wideband characteristics.

48

V. THE EFFECT OF SLOT GROUND PLANE ON IMPEDANCE BANDWIDTH

The modified rectangular slot ground plane acts as an impedance matching elements to control the impedance bandwidth of the printed antenna.

Frequency (GHz)

Figure 5. Return loss characteristics as a function of Ws

Figure 5 illustrates the simulated return loss for various Ws on the ground plane. It is shown that the return loss at the lower-edge frequency decreases as the Ws increases. But the return loss at the higher-edge frequency increases as the width slot increases. The resonance frequency at 7 GHz for Ws = 2.3 is nearly the same with Ws = 2.4 but the return loss curves for Ws = 2.3 is much better. The graph patterns of the impedance bandwidth for all variation of Ws are relatively similar which approximately cover the frequency range from 2 GHz to 11 GHz with respect -10 dB. The return loss curves of frequency approximately at 7 GHz get worse for Ws = 2.1 mm.

Figure 6 illustrates the simulated return loss for various Ls on the ground plane. The dimension for the Lg is 9mm and Wg is 30 mm. It is shown that as the Ls increases, the return loss at the lower-edge frequency decreases. But the return loss at the higher-edge frequency increases as the Ls increases. But for Ls = 6mm, the resonance frequency is different from the other variations of

Ls where it is shifted to the right for the frequency of 0.5 GHz. The graph patterns of the impedance bandwidth for all variation of Ls are similar which approximately cover the frequency range from 2 GHz to 11 GHz with respect to -10 dB. The return loss curves of frequency approximately at 7 GHz are getting worse for Ls = 3 mm.

Frequency (GHz) Figure 6. Return loss characteristics as a function

of Ls.

VI. RADIATION PATTERN

Figure 7 shows the simulated radiation pattern at different frequency for f = 3 GHz, f = 5 GHz, f = 7 GHz and 9 GHz at phi = 90º and phi = 0º. For the radiation pattern at phi = 90º, it is observed that the directivity of the antenna increases when the frequency increases. As for phi = 0º, it is observed that the radiation pattern shows a fairly omnidirectional behavior, except for the one of f = 9 GHz.

49

(a)

(b)

Figure 7. Simulated radiation pattern at f = 3 GHz, 5 GHz, 7 GHz and 9 GHz at (a) phi = 90º (b)

phi = 0º

VII. CONCLUSION

In this paper, a small rectangular printed antenna has been proposed for promising ultra-wideband applications. It is shown by CST simulation that the introduction of rectangular slot in the ground plane and size of the ground plane can be used to improve the bandwidth. The simulated return loss of antennas exhibit ultra wideband impedance bandwidth for 2 GHz to 11 GHz with respect to -10 dB. The slot on the ground plane improves the return loss for all the frequency range. The proposed antenna is small, with dimensions of 15 x 14.5 x 1.6 mm . Thus, the proposed antenna is effective for ultra-wideband applications.

VIII. REFERENCES

1. ‘FCC 1st Report and Order on Ultra-Wideband Technology,’ Feb 2002.

2. Yusnita Rahaya, Tharek Abd. Rahman, Razali Ngah, P.S Hall, “A small novel ultra-wideband with slotted ground plane,” in Proc. IEEE Int Conference on Computer and Communication Engineering 13-15 May 2008.

3. X.L Bao and M.J. Ammann, “Investigation on uwb printed monopole antenna with rectangular slitted ground plane,” Microwave and Optical Technology Letter Vol 49, no. 7, July 2007.

4. L. Wang, W. Wu, X.-W. Shi, F. Wei, and Q.-L. Huang, “Design of a novel monopole uwb antenna with notched ground,” Progress In Electromagnetics Research C, Vol. 5, 13 – 20, 2008.

5. M.A Matin, B.S. Sharif and C.C Tsimenidis, “Dual layer stacked rectangular microstrip patch antenna for ultra-wideband applications,” IET Microwave Antennas Propagation, 2007, 1, (6), pp. 1192-1196.

6. Zhi Ning Chen, Senior Member, IEEE, Terence S.P. See, and Xianming Qing, “Small Printed Ultrawideband Antenna with Reduced Ground Plane Effect,” IEEE Transaction on Antennas and Propagation Vol 55, no. 2, Feb. 2007.

7. Seok. H. Choi, Jong K. Park, Sun K. Kim, and Jae Y. Park, “A new ultra-wideband antenna for uwb applications,” Microwave and Optical Technology Letter Vol 40, no. 5, March 5 2004.

8. Mohammad Hadi Badjian, Chandan Kumar Chakrabarty, Go Chin Hock, and Sanjay Devkumar, “ An impulse uwb patch antenna with integrated bandpass filter,” Telecommunication Technology, 2008 pg 166-169.

9. Ramesh Garg, Prakash Bhartia, Inder Bahl and Apisak Ittipiboon, “Microstrip Antenna Design Handbook,” Artech House, 2001, ch. 4, pp. 284.

50