2010 IEEE International Conference on Computational Intelligence and Computing Research

ISBN: 97881 8371 362 7

Bandwidth Enhancement of Coaxial Feed U Slotted Microstrip Antenna Modeled with FDTD Algorithm

Abstract - The aim of this paper is to design a U slotted rectangular patch antenna by way of direct coaxial probe feed technique and compare it’s performance with non slotted and rectangular slotted microstrip patch antenna. The composite effect of integrating these techniques offers a low profile, high gain, broadband and compact antenna element. Parameters like return loss, radiation pattern and bandwidth are analyzed using FDTD algorithm in MATLAB. From the simulated results, Bandwidth for the rectangular slotted antenna and U slotted antenna was found to be 2.4 times and 2.84 times respectively, that of the non slotted rectangular microstrip antenna. Also better directivity was observed. The experimental results supported the same. The U slotted microstrip antenna is fabricated and the radiation pattern is measured. Details of the antenna design and simulated results are presented and discussed. Keywords - Bandwidth Enhancement, FDTDAlgorithm, microstrip Patch Antenna, Radiation pattern.

I. INTRODUCTION

With the wide spread proliferation of communication technology in recent years, the demand for compact, low profile and broadband antennas has increased significantly. A number of new developed techniques to support high data rate wireless communication for the next generation technologies have been rapidly increasing. Basically, the maximum achievable data rate or capacity for the ideal band-limited Additive White Gaussian Noise (AWGN) channel is related to the bandwidth and the signal-to-noise ratio through Shannon-Nyquist criterion: SNR)+(1log B=C 2

(1) where C denotes the maximum transmit data rate, B stands for the channel bandwidth, and SNR is the signal-to-noise ratio. From this principle, the transmit data rate can be enhanced by increasing either the bandwidth occupation or the transmission power. However, the transmission power cannot be readily increased since many portable devices are battery powered and the potential interference should also be avoided. Thus, a large frequency bandwidth seems to be the proper solution to achieve a high data rate. To meet the requirement, the slotted microstrip patch antenna has been proposed because of its low profile, light weight and low cost. However, conventional microstrip patch antenna suffers from very narrow bandwidth. This poses a design

challenge for the microstrip antenna designer to meet the broadband techniques.

There are several well-known methods to increase the bandwidth of patch antennas, such as the use of thick substrate, cutting a resonant slot inside the patch, the use of a low dielectric substrate, multi- resonator stack configurations, the use of various impedance matching and feeding techniques, and the use of slot antenna geometry. However, the bandwidth and the size of an antenna are generally mutually conflicting properties, that is, improvement of one of the characteristics normally results in degradation of the other.

Several techniques have been proposed to enhance the bandwidth in the state-of-the art antenna research. A novel single layer wide-band U slotted rectangular patch antenna with improved bandwidth has been demonstrated. By using a U-slot patch and coaxial feed, a wideband patch antenna which is small in size have been reported.

II. FDTD ANALYSIS

Fig. 1. The 3-D FDTD unit cell.

The FDTD algorithm solves Maxwell’s time-dependent curl equations by first filling up the computation space by a number of “Yee cells”. The relative spatial arrangements of the E fields and the H fields on the “Yee cell” enable the conversion of Maxwell’s equations into finite-difference equations. These equations are then solved in a time matching sequence by alternatively calculating the electric and magnetic fields in an interlaced spatial field.

The first step in designing an antenna with an FDTD code is to grid up the object. A number of parameters must be considered in order for the code to work successfully. The

D.Sugumar 1, Shalet sydney2, Dhanaraju Athina3, T.Joyce Selvahephzibah4 1, 2, 3&4Department of Electronics and Communication

Karunya University Coimbatore 641114, Tamil Nadu, India

1sugumar.ssd@gmail.com,2shaletsydney@gmail.com

2010 IEEE International Conference on Computational Intelligence and Computing Research

2

grid size must be small enough so that the fields are sampled sufficiently to ensure accuracy. Once the grid size is chosen, the time step is determined such that numerical instabilities are avoided, according to the courant stability condition. A Gaussian pulse voltage with unit amplitude, given by 22t0)--(te=V(t) T (2) where T denotes the period and t0 identifies the center time, is excited in the probe feed. In this case, the frequency domain FDTD near to far field transformation is used because it is both memory efficient and time efficient.

III. DESIGN CONSIDERATIONS OF THE PROPOSED ANTENNA

The geometries of the considered antennas are given below:

Fig. 2. Geometry of the rectangular microstrip antenna without a slot (Antenna 1) and having coaxial feed. The dimensions given in the figure are in millimeters.

Fig. 3. Geometry of the rectangular microstrip antenna with a rectangular slot (Antenna 2) and coaxial feed. The dimensions given in the figure are in millimeters.

Fig. 2, shows the geometry of the rectangular patch antenna without any slot in it and Fig. 3, shows Geometry of the broad-band rectangular microstrip antenna with a rectangular slot. As shown in Fig. 4, a U shaped slot is placed on the patch. The rectangular patch has dimensions of 57.5055 mm 47.6975 mm and is printed on a grounded substrate of thickness (h) 1.6 mm, relative permittivity (ε) 3.2 and size 60 mm ×50 mm. The values of thickness (h), relative permittivity (ε) and resonant frequency are fixed previously and patch length and width are determined using transmission line model. The patch is fed by a coaxial probe along the centerline(x axis) at a distance of L6 from the edge of the patch as shown in Fig. 2,3, and 4.

Fig. 4. Geometry of the proposed broad-band rectangular microstrip antenna with modified U-shaped slot (Antenna 3) and coaxial feed. The dimensions given in the figure are in millimeters.

TABLE 1 VALUES OF THE DESIGN PARAMETERS

Parameter Value[mm]

L 47.6975 W 57.5055 L1 3.97479 L2 11.924375 L3 3.179839 L4 19.07900 L5 11.92437 L6 26.233625 L7 4.76975 W1 18.68928 W2 21.56457 W3 11.5011 W4 6.46936875 W5 10.06347

d(relative permitivity) 3.2

smashp

Fs

Fre

Fig. 5. The pr

IV.

Coding is doslotted microsmicrostrip patcantenna is obtaslot design, thehas become mopatch antenna.

Fig. 6. Radiation plot after 4000 time

Fig. 7. Radiation ectangular slot afte

60-50

0

50

60-40

-20

0

20

40

60

roposed antenna faGha

RESULTS AN

one in matlab astrip patch anch antenna andained as followe side lobes arore prominent i

pattern of rectangue steps.

pattern of rectanger 4000 time steps

0

20

40

Ex

0

20

40

Ex

abricated at scientiaziabad

ND CONCLUS

and radiation pntenna, a recd a U slotted

ws. It is observre reduced andincreasing the

ular microstrip pat

gular microstrip ps.

020

406

Position (micro

020

40

Position (m

2010 IEE

ific instruments,

SIONS

patterns for a nctangular slottmicrostrip pated that for thed the major lodirectivity of t

tch antenna withou

patch antenna wit

6080

ons)

6080

microns)

EE International C

non ted tch

e U obe the

ut a

th a

Fig. 8. Rslot after

Bandsides oantennawidth, as the performcharactbandwian opeeach of

BW

BW

PERFORMAN

THE LOWER

Antetyp

Ante(ant

withou

Ante(antennrectan

slo

Ante(antenn

u s

Conference on Com

Radiation pattern or 4000 time steps

dwidth can bef the centre frea such as the radiation patte

range of sumance of theteristic, confoidth is the ratioeration. Using f the three cons

Hbroadband f=

broadband =(%)

NCES OF THE PROPOSED BR

R AND HIGHER FREQUENCIE

ANTENNA

2

40

60-40

-20

0

20

40

60

Ex

enna pe

FL (MH

enna 1 tenna ut slot)

181

enna 2 na with ngular ot)

172

enna 3 na with

slot) 170

mputational Intellig

of rectangular micr

e said as the equency in wh

input impedaern etc are calcuitable frequene antenna, worms to a o of the upper

equations (3)sidered antenna

Lf-

C

LH

ff-f

TABLE 2 ROAD-BAND ANTENNAS; Fc

ES WITH 10-dB RETURN LOS

A BANDWIDTH IS DETERMIN

02

0

20

Hz)

Fc (MHz)

5

1837

20

1841

00

1808

gence and Comput

rostrip patch anten

frequencies onhich the characance, polarizatulated. It can ncies within with respect specific standand lower freq

) and (4) bandas is calculated

c IS THE CENTER FREQUENC

SS IN THE OPERATING BAND

NED FROM FH-FL

040

60

Position (microns)

FH

(MHz)

1930

2000

2021

ting Research 3

nna with a U-

n both the cteristics of tion, beam be defined which the

to some dard. The quencies of dwidth for d.

(3)

(4)

CY, FL AND FH ARE

DWIDTH, AND THE

80

Bandwidth

(MHz)

115

(6.25%)

280

(15.209%)

321

(17.75%)

2010 IEEE International Conference on Computational Intelligence and Computing Research

4

Fig. 9. Simulated return loss against frequency for antenna 1

Fig. 10. Simulated return loss against frequency antenna 2

Fig. 11. Simulated return loss against frequency antenna 3

The fundamental resonant frequency of the unslotted rectangular patch antenna is at about 1.837 GHz, with an operating bandwidth of 6.25 %. Since the obtained antenna bandwidths are as large as 15.209–17.75 %, the proposed antennas show a much greater operating bandwidth, more than 2.84 times that of an unslotted rectangular patch antenna. The experimental results supported the same. Thus a new technique for enhancing the bandwidth of a

microstrip patch antenna has been developed and simulated successfully. The simulated results demonstrate that it has a better bandwidth of 17.75% at 10 dB return loss, covering from 1.700 to 2.021 GHz frequency. Techniques for microstrip broad banding, size reduction and stable radiation pattern are applied with significant improvement in the design by employing the proposed u-slotted patch shaped design and coaxial probe feed.

REFERENCES

[1] Baharudin Yatim ., Mohammed N. Shakib., Mohammad T.

Isla., Norbahiah Misran , 2009,” Design Analysis of a Slotted Microstrip Antenna for Wireless Communication” World Academy of Science, Engineering and Technology,Page: 49 .

[2] J. A. Ansari ., R. B. Ram, May 2008,” Broadband stacked U-slot microstrip patch antenna”, Progress In Electromagnetics Research Letters, Vol. 4, Page(s):17–24.

[3] Mohammad Tariqul Islam., Mohammed Nazmus Shakib., Norbahiah Misran., Baharudin Yatim, Aug. 2000,” Analysis of L-Probe Fed Slotted Microstrip Patch Antenna” IEEE Transactions on Antennas and Propagation, Volume 48, Issue 8, Page(s):1149 – 1152

[4] Mohammad Tariqul Islam., Mohammed Nazmus Shakib., Norbahiah Misran., 2009,” multi-slotted microstrip patch antenna for wireless communication” Progress In Electromagnetics Research Letters, Vol. 10, Page(s):11-18.

[5] Mohammad Tariqul Islam., Mohammed Nazmus Shakib., Norbahiah Misran., Baharudin Yatim, 25-27 December, 2008, Khulna, Bangladesh 2008,” Analysis of Broadband Slotted Microstrip Patch Antenna” Proceedings of 11th International Conference on Computer and Information Technology (ICCIT 2008), Vol. 32, Page(s):121-148.

[6] Jia-Yi Sze., Kin-Lu Wong, Aug. 2000,”Slotted rectangular microstrip antenna for bandwidth enhancement” IEEE Transactions on Antennas and Propagation, Volume 48, Issue 8, Page(s):1149 – 1152.

[7] Jeun-Wen Wu., Jui-Han Lu, June 2003,” Slotted circular microstrip antenna for bandwidth enhancement” IEEE Antennas and Propagation Society International Symposium,Volume 2, Page(s):272 – 275.

[8] Jui-Han Lu , May 2003,” Bandwidth enhancement design of single-layer slotted circular microstrip antennas” IEEE Transactions on Antennas and Propagation, Volume: 51, Issue:5, page(s): 1126- 1129

[9] Balanis constantine,Antenna theory, wiley-india, 2008.

800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800-35

-30

-25

-20

-15

-10

-5

0

5

10

800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800-35

-30

-25

-20

-15

-10

-5

0

5

800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800-35

-30

-25

-20

-15

-10

-5

0