Enhancement of gain in Microstrip Patch Antenna using EBG structure for WLAN Application

GRD Journals | Global Research and Development Journal for Engineering | International Conference on Innovations in Engineering and Technology (ICIET) - 2016 | July 2016

e-ISSN: 2455-5703

Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application 1S.Karpagavalli 2S.R.Shaaru

Nivetha 3D.S.Roland 1,2,3 Department of Electronics and Communication Engineering 1,2,3 Mepco Schlenk Engineering College, Sivakasi, Viruthunagar 626005, India Abstract In this paper, we demonstrate the performance characteristics of the gain, surface waves, return loss of microstrip patch antenna with and without Electromagnetic Band Gap structure (EBG) for WLAN application. Electromagnetic Bandgap Structure (EBG) is mainly focused on overcoming the limitation of Microstrip Patch antenna such as low gain, excitation of surface waves etc., The Microstrip Patch Antenna consists of dielectric substrate with ground plane at one end and patch at other end whereas in EBG concept, additional EBG substrate with EBG cells are inserted in between ground and dielectric substrate. The simulation is done by using High Frequency Structure Simulator (HFSS).We have obtained gain of 14.2 dB for circular EBG and gain of 8.64 dB for rectangular EBG model respectively. Hence, we improved the efficiency of the antenna the EBG model.

Keyword- Micro strip Patch Antenna, Electromagnetic Band Gap Structure (EBG), Band Gap Gain, Surface waves, Return Loss __________________________________________________________________________________________________

I. INTRODUCTION Wired LAN is replaced by Wireless LAN (WLAN) and is considered as an adjunct of wired LAN infrastructure which uses microwave band. In general there are two antennas in WLAN application which is mobile communication terminal and other is fixed WLAN base station. For base station application return loss needs to be greater than 14 dB (6). WLAN system requires low profile antenna in order to reduce the overall size of WLAN system. IEEE 802.11b is most commonly used WLAN system.

These requirements were satisfied by microstrip patch antenna. With a rapid development in wireless field, microstrip patch antenna plays a major role in antenna community. Advantages of patch antenna were low profile, low fabrication cost etc.

Excitation of surface waves is the major drawback of this type of antenna. In ordinary microstrip patch antenna, ground plane redirects one half of the radiation in opposite direction which affects the antenna gain. For complete radiation we need Îť/4 spacing in between ground plane and antenna. It is illustrated in Fig. 1.

Fig. 1: Illustration of difference in spacing between ground plane and antenna with and without EBG.

Since there is radiation in backward direction in basic micro strip patch antenna (MSA) due to back lobes we need to have infinitely large ground plane to avoid radiation in backward direction. But practically infinite ground plane is not feasible.

Excitation of surface waves in the substrate layer is main factor which reduce gain and efficiency. Surface waves occur when patch radiates, it only redirects the portion of total absorbed power. Therefore some of the power is trapped within the substrate layer.

Surface waves can be suppressed by using concept called Electromagnetic Band Gap Structure (EBG).

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Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application (GRDJE / CONFERENCE / ICIET - 2016 / 071)

II. MICRO STRIP PATCH ANTENNA In general, micro strip patch antenna (1) consists of radiating patch on one side of the dielectric substrate and ground plane on other side which is represented in Fig 2. The patch is generally made up of conducting material such as copper. The most preferred materials for dielectric substrates were FR4, RT duroid, alumina etc.

Fig. 2: Micro strip Patch Antenna

When two radiating elements such as patch and substrate are very close to each other fringing effect takes place. It is due to the presence of the Electric field arising between air and substrate. Hence, the phase velocity is different, so the dominant mode of propagation becomes quasi-TEM mode. Fringing depends on the length of the patch and height of the substrate. Fringing effect affects the resonant frequency. To overcome fringing, effective dielectric constant should be slightly less than the dielectric constant.

Fig. 3: Fringing effect

A. Design of micro strip patch antenna The design parameter essential for designing micro strip patch antenna were resonant frequency, dielectric constant and height of the substrate (3). The proposed antenna is designed for 2.42 GHz. FR4 material is used for the substrate with dielectric constant 4.4 and height of the substrate is need to be chosen according to desired frequency.

1) To calculate wavelength (λ) :λ = c/f0 where f0 is the desired frequency, c is the velocity of light.

By substituting c = 3x108 m/s, f0 = 2.42 GHz We get, λ = 0.122m=122mm 2) To calculate width of the patch (w):Width of the antenna is calculated by following equation:

(1) where, εr = relative permittivity of substrate.

By substituting known values, width of the antenna (W) = 37.6mm 3) To calculate effective dielectric constant (εr eff):-

(2)

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Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application (GRDJE / CONFERENCE / ICIET - 2016 / 071)

where, h is height of the substrate.

W is width of the patch.

By substituting known values (εr eff) = 5.142mm 4) To calculate effective length of the patch (Leff):-

(3) Then, Leff = 27mm 5) To calculate differential increase in length (ΔL):-

(4) ΔL = 0.718mm 6) To calculate actual length of patch (L):(5) L=25.564mm B. Analysis of Patch antenna without EBG This section describes the antenna model with and without EBG and its corresponding S 11 parameter Vs frequency plot. The designed antenna is simulated by using High Frequency Structure Simulator (HFSS). Microstrip patch antenna model is illustrated in Fig. 4 and its corresponding return loss VS frequency is illustrated in Fig 5.

Fig. 4: Micro strip patch antenna in HFSS

Fig. 5: S11 parameter (return loss) VS Frequency

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Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application (GRDJE / CONFERENCE / ICIET - 2016 / 071)

Fig. 6: Radiation pattern

III. ELECTROMAGNETIC BANDGAP STRUCTURE As the patch antenna radiates only portion of the total absorbed power, electromagnetic waves are trapped along the substrate. The trapped electromagnetic waves lead to the development of surface waves. The formation of surface waves leads to the radiation of the electromagnetic waves in undesired direction. The occurrence of surface waves has consequences such as reduction in gain, efficiency, front to back ratio etc. There is also formation of back lobes and side lobes etc. It is precisely important to eliminate surface waves in order to improve the performance of patch antenna.

The formation of surface waves is illustrated in Fig. 7

Fig. 7: Field lines radiated from patch illustrates formation of surface waves.

The EBG structure (2-4) is an additional layer placed above the ground plane. EBG is a periodic structure composed of dielectric, metallic or metallo dielectric material. EBG structure consists of radiating patches which is referred as EBG cells, dielectric substrate and vias. EBG structure act as LC resonant circuit (5) which has high impedance. This does not allow EM waves to propagate, it simply reflects EM waves . The presence of periodic metallic patches on EBG substrate has high impedance which does not support transverse electric (TE) and transverse magnetic(TM) field polarisation for a certain range of frequencies known as band gap. Thus, surface waves were eliminated along the structure in the band gap region. As the number of EBG cell increases, circulation of energy along EBG cell increases, hence more EM waves are reflected back which in turn increases Front to Back ratio, thereby there is an increase in efficiency and gain. EBG structure is of two types which includes one dimensional and two dimensional structure namely uniplanar and mushroom EBG. EBG patches are generally referred as EBG cells. The performance of the EBG structure depends on shape of EBG cell Some EBG cell structures were illustrated in

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432

Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application (GRDJE / CONFERENCE / ICIET - 2016 / 071)

(a) Circular EBG cell (b) Rectangular EBG cell Fig. 8: Different EBG cells A. Design of EBG Structure Among the various structure, we prefer mushroom structure because of its high impedance characteristics. The following parameters were important for designing EBG structure 1. Width of the patch (EBG patch) –‘w’ 2. Gap between adjacent patches –‘g’ 3. Height of substrate -’h’ 4. Radius of the via – ‘r’ The above parameters need to be within the following range: w = 0.04λ to 0.20λ (6) g = 0.02λ to 0.12λ (7) h = 0.04λ to 0.09λ (8) r = 0.05λ (9) where λ is the resonant frequency of the antenna.

On considering the above parameter the values obtained are, w = 8mm; g = 4mm; h = 14.9mm; r= 0.61 ‘L’ and ‘C’ are the functions of the mushroom parameter: (10) (11) The relation between resonant frequency and LC parameter (12) The value of w, g, h, r needs to be chosen according to the desired frequency.

B. Analysis of patch antenna with EBG Structure As mentioned in above section we applied a EBG concept over the basic MSA. Initially we printed a rectangular EBG cells over the EBG substrate which is placed above the ground plane. The micro strip patch antenna with rectangular EBG cell is illustrated in Fig. 9 and its corresponding plot is illustrated in Fig. 10.

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Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application (GRDJE / CONFERENCE / ICIET - 2016 / 071)

Fig. 9: MSA with rectangular EBG cell

Fig. 10: S11 parameter (return loss) VS frequency

Fig. 11: Radiation pattern

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434

Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application (GRDJE / CONFERENCE / ICIET - 2016 / 071)

Fig. 12: MSA with circular EBG cell.

Fig. 13: S11 parameter (return loss) VS frequency

Fig. 14: Radiation pattern

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Enhancement of Gain in Microstrip Patch Antenna Using EBG Structure For WLAN Application (GRDJE / CONFERENCE / ICIET - 2016 / 071)

IV. OBSERVATION The parameters such as gain, front to back ratio, return loss, efficiency, etc were discussed in this section.

A. Gain In basic micro strip patch antenna, gain obtained is 4.2 dB. On printing EBG rectangular cells over EBG substrate the gain we obtained is 31 dB due to its unique arrangement over the substrate. Due to the periodic arrangement of EBG cell there arises capacitive and inductive effect. Depending upon the structure of EBG cell the performance of EBG concept varies. We also designed circular EBG by using the same design that we followed for rectangular EBG cell. The gain obtained for circular EBG is 14.2dB. The gain gets increases when compared to basic MSA. B. Return Loss In basic microstrip patch antenna return loss obtained is 16dB whereas by using circular EBG cell return loss obtained is 23 dB. For rectangular EBG cell return loss obtained is 26 dB, performance of EBG concept varies for different structure. We also designed circular EBG by using the same design that we followed for rectangular EBG cell. The gain obtained for circular EBG is 14.2 dB. The gain gets increases when compared to basic MSA. Parameters

Basic MSA

Frequency

2.42GHz

MSA with circular EBG cell 2.42GHz

MSA with Rectangular EBG cell

Return loss

-16.52 dB

-23.18 dB

-26.3 dB

Gain

4.2 dB

14.2 dB

8.64 dB

Directivity

2.152 dBi

4.412 dBi

3.321 dBi

2.42GHz

Table 1: Performance Comparison

V. CONCLUSION In this paper, enhancement of gain for simple microstrip patch antenna is obtained by using new concept called EBG concept. This paper focussed on WLAN application. The antenna used for WLAN application requires high gain, high directivity, high return loss, low profile etc. Patch antenna satisfies above requirements and the only drawback is low gain. It is overcome by using EBG concept. Due to its periodic arrangement of EBG patches over the EBG substrate there is no chance of excitation of surface waves, thereby there is an increase in gain and other parameters.

REFERENCES [1] C.A.Balanis, “Antenna theory, Analysis and Design”, 2nd Edition.

[2] Dan Sievenpiper, Lijun zhang, Romulo F. Jimenez Broas, Nicholas G. Alexopolous and Eli Yablonovitch, “High- Impedence Electromagnetic Surfaces with the forbidden frequency band”, IEEE transactions on Microwave theory and techniques, 1999 [3] Ananias Parameswaran, Bandwidth Enhancement of Microstrip Patch Antenna using Metamaterials , IOSR Journal of Electronics and Communication Engineering (IOSR-JECE ), Dec 2013.

[4] M.N. Tan, T.A. Rahman, S.K.A. Rahim, M.T. Ali and M.F. Jamlos, “Antenna Array Enhancement Using Mushroom-like Electromagnetic Band Gap (EBG)”, Antennas and Propagation, April 2010.

[5] Sandhya Bhavsar, Prof. Bharati Singh “Electromagnetic Band Gap Structures Incorporated In Antenna Array: A Review”, International Journal of Computer Technology and Electronics Engineering (IJCTEE), March-April 2013.

[6] M.S. Alam, M.T. Islam and N. Misran, “Design Analysis of an Electromagnetic Band Gap Microstrip Antenna”, American Journal of Applied Sciences 8 (12): pp 1374-1377, 2011.

[7] Zaid A.Hamid, “Design and Implementation of a Microstrip Patch Antenna for WLAN 802.11b communication standard”, International Journal of Multidisciplinary and Current Research, 2015.

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