28th NATIONAL RADIO SCIENCE CONFERENCE

(NRSC 2011) April 26-28, 2011, National Telecommunication Institute, Egypt

Impedance Bandwidth Enhancement ofUWB Monopole Antenna by Using

Rectangular Shaped Slot

ABSTRACT

Adel B. Abdel-Rahmanl, Adel Z. El Dein2, M A. Mostafa3 IFaculty of Engineering, South Valley University-Qena

2High Institute of Energy, South Valley University, Aswan 3Telecom Egypt Company of communication, Aswan

This paper presents a new design of a wide band monopole antenna with excellent impedance matching to enhancement the impedance bandwidth. The impedance bandwidth enhancement is achieved by inserting only one rectangular shape slot on the rectangular patch of the monopole antenna instead of inserting more than one slot on the patch as usual. Also the ground plane (GP) dimensions are very important parameters in the design of these antennas, because of strong dependence of bandwidth on ground plane size. Results and performance optimizations are carried out by using the commercial EM wave simulation program and FDTD technique.

Keywords: Monopole antenna, impedance bandwidth, rectangular shape slot.

I. INTRODUCTION

In application where size, weight, cost, performance, ease of installation, and aerodynamic profile are constrains, low profile antennas like microstrip patch are required. Such applications can include wireless and ultra wideband (UWB) communication systems; the standard UWB bandwidth covers band from 3.1GHz to 1O.6GHz. The demand for these specific applications is increasing greatly due to the need of fast and uninterruptible access to information. The need of this information trade and the increase in variety of mobile communication equipment requires adaptable and miniaturized UWB antennas to be integrated within the system.

The basic form of the microstrip antenna, consisting of a conducting patch printed on a grounded substrate, has an impedance bandwidth of 1-2% this value can be improved to a wider bandwidth if a proper choice of the feeding point is considered. Because microstrip antennas inherently have narrow bandwidth (BW) and, in general, are half-wavelength structures operating at the fundamental resonant mode [1], researches have made efforts to overcome the problem of narrow BW, and various configurations have been presented to extend the BW that by inserting more than one slot on the patch [2]. Another way of improving the bandwidth to 10-20% is to use parasitic patches, either in another layer (stacked geometry) or in the same layer (coplanar geometry) [1]. However, the stacked geometry has the disadvantage of increasing the thickness of the antenna while the coplanar geometry has the disadvantage of increasing the lateral size of the antenna. It would therefore be of considerable interest if a single-layer single-patch wideband microstrip antenna could be developed. Such an antenna would better preserve the thin profile characteristics and would not introduce grating lobe problems when used in an array.

This paper presents a wideband monopole antenna with rectangular shaped slot operating in frequency range 3.1 GHz to 10.6 GHz. The single element parameters are presented and discussed. The analysis and the design of this antenna element were carried out using EM wave simulation program and FDTD technique. Furthermore, the radiation pattern of the proposed antenna element was presented and discussed.

II. PROTOTYPE ANTENNA CONFIGURATION

Figure l(a) shows the configuration of the proposed antenna, which consists of a rectangular patch with rectangular shaped slot on the patch and a partial ground plane. The antenna has a compact dimensions of 21 * 18 mm2, which is printed on a substrate of thickness 0.75 mm and relative permittivity £r=3.3. The dimension of the rectangular-slot is 8*6 mm2 and the dimension of the ground plane is chosen to be 27*38 mm2 in this study. The excitation is a 50 n microstrip line printed on the partial grounded substrate. The antenna has the following parameters: Substrate length( Lsub = 47 mm), substrate width ( Wsub = 38 mm), patch length (Lp = 18 mm), patch width(Wp= 21 mm), and ground length ( Lg = 27 mm). The applied techniques to the proposed antenna are the finite ground plane and rectangular-shaped slot on the patch, which would lead to a reasonable impedance matching. The idea of inserting a rectangular slot into the patch is to generate number of resonance frequencies that should widen the impedance bandwidth. The antenna return loss before and after inserting the rectangular-

28th NATIONAL RADIO SCIENCE CONFERENCE

(NRSC 2011) April 26-28, 2011, National Telecommunication Institute, Egypt

shaped slot is illustrated in Fig. I (b), which indicates that the return loss is greater than 10 dB over a huge bandwidth after inserting the rectangular-shaped slot.

0.75

21

18

5_1

27

38

Figure lea) Top view of the antenna Dimension by mm

47 -30

Without slot -40

With slot

-50

-60

-70 2 4 6 7 9

Figure l(b) Simulation results with and Without slot

IV. EFFECT OF THE GROUND PLANE LENGTH ON THE BANDWIDTH

The ground plane (GP) dimensions are very important parameters in the design of these antennas, because of strong dependence of bandwidth on ground plane size [3-7]. Figure 2 illustrates the return loss for different values of ground plane length Lg (Width is constant at Wsub = 38 mm). It is seen that the bandwidth is heavily dependent on GP length. The ground plane length varied from 27mm to 47mm, from the simulation results we observed that the best impedance bandwidth is at Lg = 27mm . The partial ground shows better return loss compared to full ground patch on the bottom because the antenna is transformed from patch-type to monopole­type by the partial ground.

10 11

28th NATIONAL RADIO SCIENCE CONFERENCE

(NRSC 2011) April 26-28, 2011, National Telecommunication Institute, Egypt

10

0

-10

-20

-3,0

-40 Lg=27mm

Lg=30mm -50

Lg=32mm �60

Lg=47mm

-70 2 3 4 5, 6 7 8; 9 10

Figure 2 Simulation result for the effect of the ground length on the bandwidth

11

v . EFFECT OF THE POSITION OF RECTANGULAR-SHAPED SLOT ON THE RETURN Loss

In order to further improve the overall bandwidth, rectangular-shaped slot in the patch is incorporated. A parametric analysis for the effect of the position of rectangular slot with respect to the ground plane on the return loss is shown in Figure. 3. It is clear from the simulation results that the return loss of the antenna improves dramatically as the rectangular slot moves away from the ground plane, as we stared with the distance between the slot and the ground plane (d) equal to 2mm and we ended with the distance between the slot and the ground plane (d) equal to=6mm from the simulation results we observed that the best impedance bandwidth is at d=6mm

iD �

en

0

-10

-20

-30

-40

-50

�60

-70 2 3 4 5 6 7

Frequency (GHz)

.,� .� ... - .......... .

_ _ _ _ _ _ d=2mm __ ,d=6mm

8 9 10

Figure .3. Simulation results for the effect of the slot position on the return loss

11

28th NATIONAL RADIO SCIENCE CONFERENCE

(NRSC 2011) April 26-28, 2011, National Telecommunication Institute, Egypt

VI. RESULTS AND DISCUSSION

Antenna radiation pattern demonstrates the radiation properties on antenna as a function of space coordinate. For a linearly polarized antenna, performance is often described in terms of the E and H-plane patterns [8]. The electric field (E) and magnetic field (H) planes at different frequencies are shown in Figure 4. It is obvious that the antenna behaves like a typical monopole antenna that acquires omni-directional pattern in the lower frequencies and quasi omni-directional pattern in the higher ones.

F:�GHz

-=7G z

F=10GYz

T71\

90 �3GHz

F=10GHz

.,.,/\

Plane

Figure. 4. Radiation pattern for E and H planes for different Frequencies

28th NATIONAL RADIO SCIENCE CONFERENCE

(NRSC 2011) April 26-28, 2011, National Telecommunication Institute, Egypt

Frequency (GHz) Gain (dB)

Directn;ity (dBi)

Table 1: Gain and Directivity versus Frequencies

3 4 3.10 4.26 3.15 4.57

6

5.5

5

fi) 4 .5 �

OJ (!) 4

3.5

/ 3

2.5 3 4 5

5 3.20 3.01

6

F'''' qu ency (GHz),

6 7 2.812 3.79 2.67 3.58

T 9

Figure. 5. Maximum gain in dB of the optimized proposed antenna

VII. FDTD RESULTS

8 5.73 5.5

9 5.18 5 .. 09

In this part, we compare the results obtained by EM simulation program with those obtained by the FDTD code that written in Matlab [9], to verify the obtained results. Figure. 6. Compares the values of retum loss Sll in dB that obtained by both EM simulation program and FDTD technique, in case of monopole antenna without rectangular shape slot on the patch of the antenna. Figure .7. Compares the values of return loss S 11 in dB that obtained by both EM simulation program and FDTD technique, in case of monopole antenna with rectangular shape slot on the patch of the antenna. From both two figures 6 and 7, it is noticed the results from both EM simulation program and FDTD technique are agree well with others.

0

FDTD result

-5

w --u

-10 ......

(£J

-15

-20 2 3 4 5 6 1 8 9 10

F equ e n cy GHz

Figure .6. Results of both EM simulation program and FDTD technique of monopole antenna without slot

28th NATIONAL RADIO SCIENCE CONFERENCE

(NRSC 2011) April 26-28, 2011, National Telecommunication Institute, Egypt

0

-10

-20

-30

-40 EM wave result

FDTD result

-50

-'60

-70 2 3 4 5 <6 7 8 9 10 11

Figure 7. Results of both EM simulation program and FDTD technique of monopole antenna with slot

VIII. CONCLUSIONS

A compact UWB monopole antenna which can support large bandwidth has been proposed for WLAN applications. The parametric study showed that great wideband characteristics can be achieved for a small antenna by inserting a rectangular-shaped slot on the patch of the antenna. The length of the ground plane at the bottom layer and the position of the slot with respect to the ground plane play a great rule in optimizing the return loss and the antenna radiation parameters. The antenna behaves like typical monopole antenna that acquires omni­directional pattern in the lower frequencies and quasi omni-directional pattern in the higher ones. Results and performance optimizations are carried out by using the commercial EM simulation program and FDTD technique. Simulation results with EM wave simulation are verified with FDTD technique. From the simulation of monopole antenna with FDTD, it has been seen that the 3D FDTD method is a good technique for predicating electric field propagation. The FDTD technique can be used to generate wide frequency responses with no change in modelling. Also it provides a near complete solution of Maxwell's equations in a 3D model.

REFERENCES

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[2] Mohamed H. Al Sharkawy, "MINIATURIZED WIDEBAND SLOTTED MONOPOLE ANTENNA FOR WLAN

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20.10.2010

[3] M.J. Ammann and M. John, Optimum design of the printed strip monopole, IEEE Antennas Propag Mag 47

(2005),59 61.

28th NATIONAL RADIO SCIENCE CONFERENCE

(NRSC 2011) April 26-28, 2011, National Telecommunication Institute, Egypt

[4] M. John and MJ. Ammann, Optimisation of impedance bandwidth for the printed rectangular monopole antenna,

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[6] C. Zhang and A.E. Fathy, Development of an ultrawideband elliptical disc planar monopole antenna with improved

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[7] M. John and M.J. Ammann, Integrated antenna formultiband multinational wireless combined with

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[8] Hertz, H., Electrical Waves, London, Macmillan and Co., 1893.

[9] Adel Z. El Dein, "Interaction between the Human Body and the Mobile Phone", book published by LAP Lambert

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