Effect of Slots on micrtostrip patch antenna

7/27/2019 Effect of Slots on micrtostrip patch antenna

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LETTERS

International Journal of Recent Trends in Engineering, Vol 2, No. 6, November 2009

34

Effect of Slots in Ground Plane and Patch on

Microstrip Antenna PerformanceRaj Kumar

1, J. P. Shinde

2and M. D. Uplane

3

1Defence Institute of Advanced Technology (DU), Girinagar, Pune-410025,India

Email: [email protected]&TC Department , Sinhgad Academy of Engineering, Pune

Email: [email protected] of Department of Electronics , Shivaji University, Kolhapur

AbstractThis paper presents the effect of the slots in

ground plane and patch on resonant frequency, impedance

bandwidth, gain and side lobe. The microstrip antennas

have been designed on r = 4.3 and h = 1.53 mm. It has been

observed as the slot length increases the resonant frequencyshifted to the lower side by 19.05 % and 5.04 % of

fundamental frequency of slotted patch and slotted ground

plane patch respectively. This indicates the size reduction of

slotted patch antenna is more than slotted ground plane

patch. Similarly as the slot width increases the resonant

frequency further shifted to lower frequency side. The shift

in the fr due to length variation is more in both case in

comparison to width variation. The impedance bandwidth,

Gain, side lobe and radiation efficiency effect due to slots

have also been studied. This type of study is useful to design

the compact antennas for Mobile communications.

Index TermsMicrostrip Antenna,Resonant Frequency

, slotted patch, Bandwidth and Miniaturization

I. INTRODUCTIONMobile communication systems (GSM900, GSM1800,

UMTS and PCS), wireless computer links, remote

controls, satellite mobile phones and wireless internethave shown a tremendous growth in present days. Now adays, the size of electronics needed for mobileapplications have decreased drastically, where as their

functionality has increased. The antennas required for thevarious applications should be of small size, lightweight,

low profile, broad bandwidth, low cost and integrablewith MIC/MMIC circuits [1-3]. The principal

disadvantages of Microstrip antenna is narrowbandwidth, poor efficiency and size [4]. For efficient

radiation, the size of Microstrip antenna should be /2. Ifthe size reduces less than /2, the radiation efficiency ofantenna decreases along with other antenna parameters.The miniaturization of antenna and improvement inbandwidth can be achieved by etching the slot in ground

and patch of Microstrip antenna of proper length andwidth [5-7]. This paper concentrates on the effect on

antenna resonant frequency and other antenna parametersdue to slots in patch and ground plane to design thecompact antenna with improved bandwidth andefficiency.

II. DESIGN OF RECTANGULAR MICROSTRIPPATCH

Rectangular Microstrip patch has been designed on r=4.3 and h = 1.53 mm. It is decided to design therectangular patch for 2.42 GHz. For a dielectric substrate

of thickness 'h', relative dielectric constant r and antennaoperating frequency fr. For the efficient antenna the width

and length of the patch can be calculated by

W = c/2f [(r+ 1) /2]-1/2 and L = c / 2fe 2l

Where, e l can be calculated from [8]. The antennahas also been designed using electromagnetic simulator

III. SLOT IN THE GROUND PLANE OFRECTANGULAR PATCH

In the simple rectangular microstrip patch, three slotsin the ground plane have been made as shown in Figure1. The three slots have been made along the axis ofresonating length. The two are in one side and third is inother side in the midest of two. The slot length is variedaround the axis of the resonating length of the rectangular

patch. This antenna has been studied by varying slotslength and width in the ground plane. The referenceantenna and its prototypes were designed and studied indepth using Electromagnetic simulator.

The antenna has a rectangular radiating patch ofdimensions L x W printed on the same substrate as that

used for simple reference antenna. Three identical slotsare etched in the antennas ground plane and aligned withan equal spacing of L/4 and in parallel with the patchesradiating edges or the y-axis as shown in Figure 2. In thisdesign, the slot width are kept very narrow 2mm andhave a slot length of (lin + lout) where lin and lout are the

slot lengths inside and outside the projection image of therectangular radiating patch in the ground plane. Themicrostrip patch is fed coaxially at distance of L/4 fromthe centre of the non-radiating edge for good impedancematching. The antenna has been studied usingelectromagnetic software.

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IV. NEARLY SQUARE MICROSTRIP PATCH

ANTENNA

Nearly square microstrip Patch was designed on a FR4

substrate r = 4.3 and h = 1.53mm with aspect Ratio =0.985. The microstrip patch was coaxially fed at position(- 4.5, - 5.5) mm along the diagonal as shown in Figure 3.

The 4 slots have been etched in patch. The effect of slothas been studied by varying length and width of slot.The effect on impedance bandwidth, half powerbeamwidth, gain and efficiency has been measured as theslot length and width varies.

Figure 1.Microstrip Rectangular Figure 2. Slotted ground planePatch Antenna Rectangular Microstrip Patch

Figure 3. Nearly Square Microstrip Patch with Four Slots

IV. RESULTS AND DISCUSSIONA. Slot in Ground plane

The simple rectangular microstrip patch antenna Ref.and its four prototypes of the proposed antenna (Rect-1 to

4) were designed on a FR4 substrate r= 4.3 and h = 1.53mm. The dimensions of the microstrip patch have beentaken L x W = 29.57 x 38.08 mm at the fundamentalresonant frequency of fr = 2.42 GHz. The slot length lout

for the prototypes was fixed to be (L/4) and the slot

length lin is varied in steps of 2 mm from 10 mm to 16mm. The reference antenna is having lin = lout =0.The feed position has been taken 5.3 mm down from

the centre of the antenna. The effect of embeddingmeandering slots length on the return loss and resonant

frequency is clearly visible in Figure 4. From the Figure4, it is clear as the slot length increases, the fundamentalresonant frequency shifted to lower frequency side whichindicates the size reduction of antenna. For a fixed lout,but with increasing lin it is observed that the fundamentalresonant frequency is lowered. In the case of rect-1 with

the slot lengths of 10 mm the resonant frequency isinitially shifted to 2.353 GHz with Return loss 18.58

dB, BW 37.2 MHz, directive gain of 6.908dBi andradiation efficiency of 93.27%. The Rect-2 exhibits themaximum bandwidth 38.8 MHz and rect-4 exhibits 17.7MHz bandwidth as shown in table 1. The measured

radiation efficiency of the ref. antenna is 87.89%. The

efficiency increases to 93.27% for rect-1, 91.55% for

Rect-2, 98.10% for rect3, and 92.45% for rect-4.Table 2 shows the behavior of fundamental frequency

as the slot width varies. As the slot width of Rect -2antenna increases from 1 mm to 6 mm, the resonantfrequency shifted slightly to lower side. The impedancebandwidth of Rect - 2 antennas with width 2mm exhibits

maximum bandwidth 42.9 MHz. The gain of the antennaincreases by 0.32dB and efficiency by 6.28%.

Figure 4. Simulated Return loss Vs Frequency of Rectangular

Microstrip Antennas

TABLE 1PERFORMANCE COMPARISON OF THE PROPOSED ANTENNAWITH DIFFERENT SLOTS LENGTH IN GROUND PLANE

r= 4.3, h = 1.53mm, L = 29.57mm, W = 38.08mmAnt. lin

mmfr

GHzR. L.(dB)

BWMHz

Gain(dB)

%

Ref. 0 2.42 -22.55 36.2 7.293 88.84

Rect-1 10 2.353 -18.58 37.2 6.908 93.27

Rect-2 12 2.339 -22.23 38.8 7.389 91.55

Rect-3 14 2.313 -44.52 31.3 7.30 98.10

Rect-4 16 2.298 -11.91 17.7 7.251 92.45

TABLE 2

PERFORMANCE COMPARISON FOR RECT- 2 FOR DIFFERENT

SLOT WIDTHS IN THE GROUND PLANE

SlotWidth

(mm)

fr(GHz)

Returnloss

(dB)

Gain(dB) %

BWMHz

1 2.3999 -9.018 7.035 92.40 ---

1.5 2.3901 -27.68 7.007 91.65 39.9

2 2.377 -20.39 7.005 91.55 42.9

2.5 2.3493 -19.84 7.065 92.59 41.5

3 2.3454 -20.16 7.103 93.32 39.5

4 2.3417 -22.23 7.362 98.29 38.8

5 2.3381 -22.88 7.326 98.68 37.6

6 2.3359 -23.16 - - 36.6

TABLE 3

COMPARISON OF VARYING SLOT LENGTHS AND WIDTH OFNEARLY SQUARE MICROSTRIP PATCH

Slot width 1.5 mm Slot length = 5mm

Slot

L

mm

fr

GHz

R.L.

(dB)

Gain

(dB)

Slot

Width

mm

fr

(GHz)

R. L.

(dB)

Gain

(dB)

3 1.714 -23.29 6.106 1 1.714 -22.61 6.11

5 1.704 -31.94 6.109 1.5 1.704 -31.74 6.12

8 1.608 -30.54 5.98 2 1.694 -29.41 6.10

10 1.544 -18.72 5.865 2.5 1.686 -31.17 6.09

12 1.465 -15.22 5.588

14 1.388 -17.19 5.570

B. Slot in Patch

Nearly square microstrip Patch was designed on a FR4

substrate r= 4.3 and h = 1.53mm. The 4 slots have been



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made by etching in the patch. The effect of slot has beenstudied by varying length and width of slots. Table 3reveals as the length of slot varies from 3 mm to 14 mmwith fix width 1.5mm, the resonant frequency of thepatch shifted from 1.714 GHz to 1.388 GHz i.e 19.05 %down of fundamental frequency The simulated gain of

antenna decreases drastically from 6.106 dB to 5.57 dB.

With the varying length, efficiency and impedancebandwidth of the patch are also decreases as shown inTable 6. Table 3 also shows the effect of width on theantenna parameters. As the width of slot increases from 1mm to 2.5 mm, the resonant frequency shifted lower side

from 1.7148 GHz to 1.6861 GHz. The gain, HPBW,efficiency and impedance bandwidth remain almost same

as shown in table 3 and table 6.

TABLE 4 TABLE 5

COMP. OF RADIATION ANTENNA RECT.2 FOR

PATTERNS OF PROPOSED FOR DIFFERENT SLOT WIDTHSANTENNA

V. RADIATION PATTERN MEASUREMENTThe radiation patterns of all the antennas were

simulated for the entire prototype antenna Rect-1 to Rect-4. In table 4, the Gain (dB), Half Power Beam Width(HPWB) and side lobe in dB have been tabulated. It is

observed as the slot length increases, the side lobe remainsame except the rect -1 antennas the side lobe level isbetter around 15.4 dB in comparison to other antennas.

A Good broadside Radiation pattern HPBW of 89.3 isobserved for rect-1and 71.1 for rect-4. Table 5 shows asthe slot width increase from 1 mm to 5mm, the HPBWvaries from 70.8 deg. to 69.7 deg. and side lobe levelsremain almost same. Table 6 shows, for nearly squarepatch the HPBW decreases from 114.9 deg. to 100.6 deg.as slot length increases from 3 mm to 14 mm. But effect

of width on HPBW, efficiency and BW is negligible fornearly square patch as shown Table 6. The radiationpatterns of Rect.-1 antenna have been shown in Figure 5.

TABLE 6

COMPARISON OF VARYING SLOT LENGTHS AND WIDTH OF

NEARLY SQUARE PATCH

VII. CONCLUSIONS

The Rectangular Microstrip Patch Antenna has beenanalyzed for the varying slot lengths and width in patch

and the ground plane of the antenna. It is demonstrated asthe slot length and width increases, the resonant

frequency shifted towards lower side. The effect onresonant frequency shift is more pronounced for slots inpatch than slots in ground plane. This indicates the moresize reduction due to slots in patch in comparison to slotsin ground plane. It has been observed that bandwidth andgain are more affected due to slot in patch than slot in

ground plane. The return loss variation exhibits

impedance match as the function of slot length and width.By proper selection of feed, slot length and width, theantenna performance can be optimized which can beeffectively and efficiently utilized for mobilecommunications Applications.

Figure 5. Radiation patterns of Rect 1 antenna.

ACKNOWLEDGEMENT

Authors acknowledge the support of all the staff ofDepartment of Electronics Engg., Defence Institute ofAdvance Technology, Girinagar, Pune and the researchscholar of Microwave and Millimeter wave Antenna Lab.

REFERENCES

[1] D. M. Pozar and D. H. Schaubert ed., MicrostripAntennas, New York, IEEE Press.

[2] K. R. Carver and J. W. Mink, Microstrip antennatechnology, IEEE Trans.,AP-29, pp. 2-24, Jan. 1981.

[3] R. Garg, Progress in Microstrip antennas , IETETechnical Review, Vol. 18,No.2 & 3 pp .85-

98,March-June 2001.

[4] R. B. Waterhouse, S. D. Targibski and D. M.Koktoff,Design and performance of small printed

antenna, IEEE Trans.,AP-46, 11, Nov. 1998, P. 1629[5] S. Dey and R. Mittra, Compact Microstrip patch

antenna, MOTL, Vol. 13, Sept. 1996, p. 12.[6] K. L. Wong and W. S. Chen,Compact Microstrip

Antenna with dual frequency operation, ElectronicsLetters Vol. 33, no. 8, April 1997, p. 646.

[7] R. M. Vane aet.al,A shorted Rectangular Microstrip

Antenna with slots in ground plane, IE(I), Journal-ET, Vol. 87, July 2006, pp. 19-20.

[8] M. Kirchning et.al,Accurate Model for open endeffect of Microstrip line, Electron.

Lett.17,Feb.1981, pp. 123-5.


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Effect of Slots on micrtostrip patch antenna