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International Conference on Computational Systems in Engineering and Technology, March 7 & 8 2014, Chennai

Design and Development of Antipodal LinearlyTapered Slot Antenna Using Substrate Integrated

Technology for Wireless Communications

M. Vidhya 1, M.E.,ECE. Valliammai Engineering CollegeKancheepuram, [email protected]

Mr. S. Ramesh 2, M.Tech.,(Ph.D), AP (Sel.G)ECE. Valliammai Engineering CollegeKancheepuram, [email protected]

Abstract A high gain, low cost, and efficient antenna isdesigned using the concept of Substrate Integrated Waveguide(SIW) and Antipodal Linearly Tapered Slot Antenna (ALTSA)for wireless communications. Antipodal designs are easy tomatch with the feeding systems. The metallization of either sideof the substrate is flared in opposite direction to form the taperedslots. SIW is used as the feeding system. SIW consists of substratewith metalized vias acting as two side walls ina dielectric substrate by densely arraying metallized posts or via-holes which connect the upper and lower metal plates of thesubstrate. The proposed antenna can be designed usingcommercial 3D Electromagnetic Simulation software- ComputerSystem Technology (CST). The parameters to be measured areReturn loss, VSWR, Gain & Radiation pattern.

Keywords Anti podal l inearly tapered slot antenna; Dielectri cloadin g; Substrate in tegrated waveguide.

I. I NTRODUCTION

Due to the easy integration and large bandwidthrequirements, Tapered Slot Antenna (TSA) is chosen to be theantenna configuration that will be studied within the scope ofthis work. Tapered slot antennas (TSA) [1-2] are travellingwave antennas. In general, all antennas whose voltage orcurrent distribution can be modeled by one or more travellingwaves are called travelling wave (nonresonant) antennas.Tapered slot antenna uses a slot line etched on a dielectricmaterial, which is widening through its length to produce anendfire radiation. An electromagnetic wave propagatesthrough the surface of the antenna substrate with a velocityless than the speed of light which makes TSAs gain slow waveantenna properties. The EM wave moves along the

increasingly separated metallization tapers until the separationis such that the wave detaches from the antenna structure andradiates into the free space from the substrate end. The E-

plane of the antenna is the plane containing the electric fieldvectors of the radiated electromagnetic (EM) waves. ForTSAs, this is parallel to the substrate since the electric field isestablished between two conductors that are separated by thetapered slot. The H plane, the plane containing the magneticcomponent of the radiated EM wave runs perpendicular to thesubstrate.These three main types of TSAs are compared [2] interms of beamwidths and side lobe levels. Three types are

Constant width tapered slot antenna (CWSA), LinearlyTapered Slot Antenna (LTSA), Vivaldi tapered slot antenna(VTSA).

For a TSA with the same antenna length, aperture widthand substrate parameters, CWSA has the narrowest

beamwidth, followed by LTSA and then Vivaldi. The sidelobelevels are highest for CWSA, followed by LTSA and thenVivaldi. So a transition between the LTSA and CWSAstructures could provide reconfigurability about antenna

beamwidth and sidelobe levels. LTSA [2] consists of a slotline that gets wider linearly through the antenna length. Thereare basically three main parameters that determine theradiation characteristics of a LTSA [1]. These are Antennalength (L), Aperture width (W), Ground extension (H). Duringthe literature survey about TSA, it is found that conventionaltapered slot antenna suffers from poor directivity in the lower

part of band. Consequently in this paper, it is aimed toinvestigate the radiation characteristics of ALTSA and toexplore the possibility of improving the radiation pattern anddirectivity of ALTSA.

A broadband high gain antipodal linearly tapered slotantenna was designed with substrate integrated waveguide.SIW was to build artificial channels using metallic vias withinthe substrate to guide the waves. SIW [3] is to remove the

bandwidth limitation. A tapered slot antenna uses a slot lineetched on a dielectric material, to produce an endfire radiation.ALTSAs [4] have moderately high directivity (on the order of10-17 dBi) and narrow beamwidth. Thus entire structure iseasy to fabricate in a planar single layer substrate resulting inlow cost and easy fabrication. Advantage of this antenna ishigh gain and lower side lobe level. In order to increase thegain and reduce the side lobe level, dielectric loading [5]-[6]are added. Dielectric slab is designed with same dielectricconstant and thickness of the antenna substrate. Now theantenna has shorter structure, easy to fabricate and high gain.

II. DESIGN OF ALTSA

The proposed antenna structure in this work is designed on aRogers Duroid5880 substrate with a dielectric constant of 2.98at 7 GHz. In this demonstration, a relatively thick substrate isused to lower the conductor loss of SIW and also to facilitate


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the fabrication process. The design procedure of SIW that was presented is utilized to calculate the spacing between twoadjacent vias (S) and the width of SIW (W).

In ALTSA, Antipodal doubles the input impedance of theLTSA. It has better VSWR or S11.Cross polarization levelsare higher in antipodal designs. Antipodal designs are easy tomatch with the feeding systems. This is required to rotate the

SIW E-field, which is perpendicular to the substrate as itwould be within the equivalent waveguide structure. Theantipodal flares ensure that this field is translated into the E

plane of the LTSA as the flares become more and moreseparated, the horizontal electric field is rotated into thevertical H plane parallel to the antenna substrate. Themetallization of either side of the substrate is flared inopposite direction to form the tapered slots. To solve a

potential mismatch problem, the flaring metals are designed tooverlap with each other is shown in Fig. 1 . Then, the proposedantenna has higher gain and also shorter structure, but it has awider configuration.

Fig. 1. Structure of ALTSA antenna .

Aperture width of the slot is given by

(2)

Where thickness of the substrate (t)- 0.8 mm, Dielectricconstant ( ) - 2.98, H-Height of the substrate.

Length of the tapered slot antenna is given by

(3)

(4)

In high frequency applications, microstrip devices arenot efficient, and because wavelength at high frequencies aresmall, microstrip device manufacturing requires very tighttolerances. At high frequencies waveguide devices are

preferred; however their manufacturing process is difficult.Therefore a new concept emerged: substrate integratedwaveguide. SIW is a transition between microstrip and

dielectric-filled waveguide (DFW). Dielectric filledwaveguide is converted to substrate integrated waveguide(SIW) by the help of vias for the side walls of the waveguideas shown in Fig. 2 .

Fig. 2. Dimensions for SIW.

For a rectangular waveguide, cut off frequency of arbitrarymode is found by the following formula

(5)

Where c is speed of light, m and n are mode numbers, a and bare dimensions of the waveguide.

For TE 10 mode, the much-simplified version of this formula is

(6)

For DFW with same cut off frequency, dimension is found by

(7)

Having determined the dimension for the DFW the designequations for SIW is as follows

(8)

In published articles about SIW design, the following twoconditions are required.

(9)

Where guided wavelength is expressed as follows.

(10)

(1) t25.1

41.133.0exp

H48.7w

r

r

o 003.0H

eff r f

c 2

L

r eff r 121

22

bn

am

2

c f c

ac

f c 2

r d

aa

sa

pd aa d s 95.0

2

5 g d

d p 2

22

22

2

ac

f r g


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SIW devices can be thought as a form of dielectric filledwaveguide (DFW), therefore the starting point can be DFW.For TE 10 mode, the dimension "b" is not important as it doesnot affect the cut off frequency of the waveguide. Thereforethe substrate can be at any thickness; it only affects thedielectric loss (thicker=lower loss).

III. RESULTS AND DISCUSSION

SIW fed LTSA is simulated using CST. For this particular antenna, the results taken into considerations wereReturn Loss, VSWR, Radiation Pattern and Gain of theantenna. The maximum gain of 4.275 dBi was obtained for asingle element antenna. Fig. 3 shows the measured return lossof the SIW fed ALTSA. The S11 is -20 dbi at 7GHz. Fromthis result, the resonance frequency of the proposed antenna is7 GHz.

TABLE I. Dimensions of ALTSA antenna.

PARAMETER VALUES

Frequency 7 GHZ

Impedence 50

Substrate Rogers RT 5880

Slot length 6 mm

Slot Width 5 mm

Tapered Length 15 mm

Fig. 3. |S11| of ALTSA.

Fig. 4 and Fig. 5 shows the measured VSWR andradiation pattern of the SIW fed ALTSA. The VSWR is 1.3 at7 GHz. Fig. 6 shows the far field of ALTSA and Table. I givesthe dimensions of the Antipodal linearly tapered slot antenna.The proposed antenna is designed for wireless applicationsoperating at 7GHz. Antenna is designed using Rogers RTDuroid 58880 substrate.

Fig. 4. VSWR of ALTSA Antenna.

Fig. 5. ALTSA radiation pattern .

Fig. 6 Far field of ALTSA.


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IV. CONCLUSION

The SIW fed antipodal linearly tapered slot antennaoperating at 7 GHz for wireless communications have beenstudied and optimized in this paper. It is designed on a RogersDuroid5880 substrate with a dielectric constant of 2.98. TheSIW and ALTSA are jointly used to design a low cost, high

gain and efficient antenna. It has better VSWR or S11. Cross polarization levels are higher in antipodal designs. Thisantenna structure can easily be transplanted into higherfrequency range. The low cost printed circuit board process isused to fabricate the antenna structure in single layer structure.

REFERENCES

1. Nasser Ghassemi, Ke Wu, PlanarHigh gain dielectric-loadedAntipodal linearly tapered slot antenna for E- and W-BandGigabyte point-to- point Wireless Services, IEEE Transactionson Antennas and Propogation, Vol 61, pp. 1747-1755, April 2013.

2. Vivek Unadkat, VedVyas Dwivedi, Design of CorrugatedLinearly Tapered Slot Antenna for Wireless Application ,Germany, LAP Lambert Academic Publishing, June 2013.

3. R.Kazemi, E.Fathy, and R. Sadaghzadeh, Dielectric rod antennaarray with substrate integrated waveguide planar feed network forwideband applications, IEEE Transactionson Antenna andPropogation., Vol. 60, no. 3, pp.1312-1319, March. 2012.

4. Lev Pazin and Yehuda Leviatan, "A Compact 60-GHz TaperedSlot Antenna Printed on LCP Substrate for WPAN Applications", IEEE antennas and wireless propogation letters, Vol 9, pp.272-275, 2010.

5. Z.Wang, C.C. Chiau, X. Chen, B.B.S. Collins, S. P. Kingsley,S.C. Puckey, Broadband dielectric loaded trapezoidal planarantenna, APMC Proceedings, Vol 4, 2005.

6. Chung-Tung Cheung, Cheh Ming-Liu, Po-Aun sung, David B.Rutledge, A Novel Dielectric Loaded Antenna For WirelessApplications, Antennas and Propagation Society InternationalSymposium, Vol 1, pp. 38-41, 1999.

7. H. Wang, D.-G. Fang, B. Zhang, and W.- Q. Che, Dielectricloaded substrate integrated waveguide (SIW) H-plane hornantennas, IEEE Trans. Antennas Propag ., vol. 58, no. 3, pp. 640 647, Mar. 2010.

8. D. Deslandes and K.Wu, Integrated microstrip and rectangularwaveguide in planar form, IEEE Microw. Wireless Compon.

Lett ., vol. 11, pp. 68 70, Feb. 2001.

9. D. Stephens, P. R. Young, and I. D. Robertson, W -bandsubstrate integrated waveguide slot antenna, Electron. Lett. , vol.41, no. 4, pp. 165 167, Feb. 2005.

10. Lev Pazin and Yehuda Leviatan, "A Compact 60-GHz TaperedSlot Antenna Printed on LCP Substrate for WPAN Applications",IEEE antennas and wireless propogation letters, Vol 9, pp.272-275, 2010.

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