ISSN: 2379-3686 International Journal of Science Research and Technology

Volume 1 Issue 1, p p 9-16 , 15th

September 2015

9

Comparative investigation of Graphene Nano Patch

Antenna for different Substrate Materials in

Terahertz Region 1Rajni Bala ,

2Anupma Marwaha

1Research Scholar,

2 Associate Professor

1,2Department ECE, SLIET, Deemed-University, Sangrur, Punjab,India

Abstract: The dielectric substrate material is entirely

important in terms of controlling bandwidth as well as

radiation efficiency. The possibility of using appropriate

dielectric materials for graphene antenna design has been

explored and their effect on radiation characteristics of

rectangular patch antenna such as return loss, bandwidth,

gain, directivity, radiation efficiency, voltage standing wave

ratio (VSWR), absorption cross section and radiation pattern

has been further investigated. The present study performs to

comparative analysis of graphene based nano patch antenna

resonating around 2.9THz for five dielectric substrates

namely duroid, polyamide, quartz, silica and silicon. Finite

element method (FEM) based high frequency structure

simulator (HFSS) software has been used for carrying out the

numerical simulation. It is clear from the various results in

terms of return loss, gain, radiation efficiency, bandwidth,

front to back ratio and VSWR that the graphene nano patch

antenna based on silicon substrate realizes better

characteristic as compared to other substrate materials.

Keywords: Graphene, Substrate materials, Rectangular nano

patch antenna , Terahertz region, HFSS.

I. INTRODUCTION

Nanotechnology is the study of manipulating material on a

molecular scale and atomic scale. Richard Feynmann

explained the process of manipulating individual atoms and

molecules using a down-scaling approach based on the

equivalence of a mechanical device. Only recently

advances in technology such as the successful production

of graphene has attracted the attention of researchers.

Although the possibility to use graphene as antenna in

different frequency domains such as GHz, THz and optical

range has been studied theoretically but there is still very

less experimental validation has been performed. Graphene

is the name given to a flat monolayer 2D sheet of carbon

atoms are scattered at the edges of regular hexagons tightly

packed in a honeycomb lattice and very thin atomic

thickness of 0.345nm makes it unique.. The properties of

graphene make it an area under discussion of potential

recent research into latent technological applications,

ranging from ultra-high-speed transistors to transparent

solar cells and also very interesting systems for novel

electronics applications. Graphene has been recommended

for use in patch antenna for implementing electromagnetic

communications between nano-systems outstanding to its

ability to support Surface Plasmon Polaritons. Graphene

has a plasmonic resonant frequency in the THz regime (0.1

- 10THz) making it well suitable for use as a plasmonic

nano-antenna. A rectangular nano patch antenna (NPA)

consists of a conducting portion placed above a perfect

conducting ground-plane. The patch and ground-plane are

separated by a dielectric substrate material [1]. In the

previous work carried out by numerous researchers, the

patch conductor normally used for patch antenna is the

copper material [1-2]. The use of nanotechnology will

result in less power consumption, cheaper, smaller in size

and provides improved performance for wireless

communications. A lot of demand for various portable

wireless communication devices to provide more bendable

applications in a small device. The semiconductor industry

is working for improving the performance of electronic

systems for the last few decades by making ever-smaller

devices which may however face both scientific and

technical limits. The industry therefore is now searching

for other alternative device technologies using different

substrate materials which may be able to produce higher

performance and better functionality. However graphene

has been used in the present work which has great potential

for future nano devices [3-4].The substrate material used in

antenna design not only provides mechanical strength to

antenna, but it also assists in providing variations in

radiation characteristics by suitably selecting the substrate

material. For better antenna performance it is mostly

desirable to have thick substrates having lower values of

dielectric constant which enhances the fringing fields

accounting for radiation, but higher values may also be

used in special conditions [5]. Further intelligent decision

while the cost of antenna design is also affected by

dielectric material, hence it requires selecting substrate. For

graphene based antenna, the presence of substrate material

additionally aids in establishing clear visibility of the single

layer graphene patch [6-7]. From the literature different

ISSN: 2379-3686 International Journal of Science Research and Technology

Volume 1 Issue 1, p p 9-16 , 15th

September 2015

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studies are available on the use of various substrate

materials for graphene based nano-patch antenna [8-10]. In

the present analysis, the detailed comparative analysis has

been performed with duroid (εr =2.2), polyamide (εr =3.5),

quartz (εr =3.78), silica is just another name of silicon

dioxide (εr =3.9) and silicon (εr =11.9). The rectangular

nano patch antenna considered here for investigation

basically resonates around 2.9 THz.

II. DESIGN OF A RECTANGULAR NANO PATCH ANTENNA

Graphene-based plasmonic nano-antennas, having

dimensions of the order of few micrometers have been

revealed to radiate the electromagnetic waves in terahertz

band [4], with appreciably higher radiation efficiency with

respect to the metal patch antenna correspondingly. The

unique properties of graphene will also allow to improve

the performance of antennas at the nanoscale. The edge fed

graphene based rectangular nano patch antenna has been

designed in this paper for operating at resonant frequency

of 2.9THz.The rectangular nano patch antenna consisting

of a conducting patch and a ground plane separated by a

thin dielectric substrate is designed here as shown in Fig.1.

The side length of rectangular nano patch antenna is ''Lp'',

printed on a substrate of height ''h'', having a relative

dielectric constant of ''εr''. The model of graphene patch

antenna is created on FEM based HFSS software with

physical dimensions of radiating patch having length

Lp=23µm and width Wp=31µm. The length of patch has

been calculated using SPP dispersion relation of graphene

antenna resonance condition [11]. The patch antenna is fed

by a microstrip line feed (L2 × W2) with quarter wave

transformer (L1 × W1) with following dimensions as

detailed in Table 1. The rectangular nano patch antenna is

designed by considering the height of the substrate h, as

3µm, length of substrate as Ls = 103µm and width of the

substrate as Ws = 104µm. The substrate made of different

materials selected are for comparative analysis as duroid (εr

=2.2), polyamide (εr =3.5),quartz (εr =3.78), silica is just

another name of silicon dioxide (εr =3.9) and silicon (εr

=11.9).

Table 1: Dimensions of graphene based terahertz rectangular NPA

Parameter Value

Operating frequency band (fo) 2.83 -2.96 THz

Substrate length and width(Ls × Ws) 103 µm × 104 µm

Substrate thickness (h) 3 µm

Side length and width of square patch (Lp × Wp) 23 µm × 31 µm

Length and width of edge feed

(λ/4 transformer) (L1 × W1)

14.5 µm × 1.4 µm

Length and width of feed (L2 × W2) 23 µm × 5 µm

Fig. 1. Graphene based rectangular patch antenna

At microwave and THz frequencies, the graphene scalar

conductivity as a function of bias electric field essentially

follows Drude-like behaviour [12-13]. One atom thick

graphene can exhibit mobility value as high as 20,0000

cm2V

−1s

−1 [14].The mobility of graphene selected here is

18,0000 cm2V

−1s

−1. It has ability to withstand current

density of 108A/cm

2, high charge carrier concentrations,

transmittance of about 97% of visible light and high

thermal conductivity of the order of 5 × 103 W/mK.

Graphene’s non-electronic property was found to have a

Young’s modulus of 1.0 TPa which is an outstanding value

[15-17].The parameters chosen for graphene patch here are

chemical potential, µc= 0 eV, scattering rate, Γ = 1meV, at

room’s temperature T = 300K [18-20][21-22].

III. RESULTS AND DISCUSSION

By using HFSS software, simulation was carried out to

analyze graphene based rectangular nano patch antenna for

varying dielectric constant values of the different substrate

materials. Fig. 2 depicts the return loss S11 plotted as a

function of frequency in the range of 2.83-2.96 THz

demonstrating the impedance matching conditions for

different substrate materials as Duroid (pink double dot

line), Polyimide (green dotted line), Quartz (blue short

dashed line), Silica (purple solid line) and silicon (red

solid line). It can be observed that return loss value for

different materials reach their peak values below -10dB at

resonating frequency around 2.9THz for all the selected

substrates. Moreover it is clear that the best matching

conditions are however achieved for silicon with return

loss reaching the maximum value of -28.39dB at resonating

frequency of 2.9 THz. The antenna resonates at 2.9THz in

contrast to the selected design frequency of 2.83 THz, the

ISSN: 2379-3686 International Journal of Science Research and Technology

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shift in frequency being caused due to the fringing fields

from the sides of the patch.

Fig. 2. Return Loss (in dB)

Fig. 3 depicts the corresponding VSWR values agreeable

the required conditions with values as 1.42 for duroid, 1.69

for polyamide, 1.42 for quartz, 2.58 for silica and 1.08 for

silicon at their respective resonating frequencies. Fig. 4

shows the 2D antenna gain plotted as function of resonant

frequency for different substrate materials. It can be clearly

seen that reasonably good dB gain with value more than 5

dB is achieved in the operating frequency band for all

proposed substrate materials. However for graphene as

patch material on silicon substrate material, the gain is 6.48

dB which is quite high than for substrates. The 3D (polar

plot) radiation patterns for gain and directivity for silicon

substrate material are as plotted in Fig. 5, keeping the other

dimensions of antenna model as given in the above section.

Fig. 3. VSWR curves for various substrates materials

ISSN: 2379-3686 International Journal of Science Research and Technology

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Duroid (pink double dot line), Polyimide (green dotted line), Quartz (blue short dashed line), Silica (purple solid line) and silicon (red solid line)

Fig. 4. Gain plot (in dB) for various substrates materials

Duroid (pink double dot line), Polyimide (green dotted line), Quartz (blue short dashed line), Silica (purple solid line) and silicon (red solid line)

(a) Gain ( in dB)

(b) Directivity ( in dB)

Fig. 5. 3D radiation patterns with Silicon substrate material

Fig. 6 shows the plots of 2D radiation pattern for dB gain

in the azimuth plane for all the substrates. The radiation

pattern is a graph which demonstrates the variation of

actual field strength of electromagnetic field at all the

points equidistant from the antenna radiation pattern graph

(ϕ = 0o

with "red colour" and ϕ = 90

o with "green colour").

The plots here indicate very much reduced back lobe level

for the silicon substrate material.

(a)

(b)

ISSN: 2379-3686 International Journal of Science Research and Technology

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(c)

(d)

(e)

Fig. 6. 2D Radiation patterns (a) Duroid, (b) Polyimide, (c) Quartz, (d)

Silica and (e) Silicon

The 3D E-field radiation patterns for different substrate

materials of given antenna are shown in Fig. 7.

(a)

(b)

ISSN: 2379-3686 International Journal of Science Research and Technology

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(c)

(d)

(e)

Fig. 7. 3D Radiation patterns (a) Duroid, (b) Polyimide, (c) Quartz, (d)

Silica and (e) Silicon

The comparative analysis of radiation parameters of

rectangular nano patch antenna with graphene material for

various substrate materials is shown in Table 2. Increased

atmospheric absorption make attractive THz

communication systems for WLAN antenna applications

with secure and ultrahigh bandwidth. Here the antenna

radiates with maximum absorption cross section for silicon

material with value of 99.9 dBm. Further it provides

excellent response with maximum radiation efficiency over

82.2% and sufficient bandwidth enhancement. Minimum

Table 2: Comparative comparison of rectangular nano patch antenna for various substrate materials

Parameters/Substrate

Materials

Dielectric Constant

Resonating

Frequency

Return

Loss

(dB)

Gain

(dB)

Directivity

(dB)

Minimum

VSWR

Value

Absorption

Cross Section

(dBm)

Front

to

Back

Ratio

Radiation

Efficiency

(%)

Bandwidth

(GHz) where

S11 = -10dB

Duroid εr =2.2 2.90 -15.20 5.54 7.01 1.42 96.7 110.6 71.4 105

Polyimide εr =3.5 2.90 -15.72 5.54 7.13 1.69 97.3 111.2 71.6 110

Quartz εr =3.78 2.94 -14.64 5.43 6.80 1.42 96.9 75.2 73.8 90

Silica εr =3.9 2.86 -11.21 5.89 6.92 2.58 80.6 127.6 69.6 100

Silicon εr =11.2 2.90 -28.39 6.48 7.46 1.08 99.9 40.9 82.2 120

ISSN: 2379-3686 International Journal of Science Research and Technology

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front to back ration of 40.9 indicates lesser back lobe level

for the silicon substrate material. Therefore it can be

concluded that silicon is the most appropriate substrate

material with value of 99.9 dBm. Further it provides

IV. CONCLUSIONS

In this paper, an effort has been made deal with comparative

investigation of different substrate materials for graphene

based microstrip edge feed rectangular nano patch antenna for

terahertz region. The simulation is numerically solved

considering zero chemical potential for graphene material for

simpler implementation on FEM based HFSS simulation

software is used for numerical modeling of the designed

antenna. The quarter wave fed patch antenna of graphene

parameters are optimized for operation in band of frequencies

in the range 2.83-2.96 THz. The substrate material as silicon

attains maximum return loss value of -28.39 dB with

acceptable value of VSWR. The gain and directivity obtained

are 6.48 dB and 7.43 dB respectively. The -10 dB bandwidth

for silicon observed from the return loss plot is 120 GHz

which shows much improvement in bandwidth as compared

with other substrate materials as evident from Table 2.

Moreover the antenna exhibits absorption cross section above

80% over the entire band of frequencies for all proposed

substrate materials. It has been concluded that proper

selection of substrate material and patch dimensions are key

features in achieving desired return loss, gain, directivity,

acceptable VSWR, bandwidth and radiation efficiency. The

accurate modeling further provides excellent response with

maximum radiation efficiency over 82.2% and sufficient

bandwidth enrichment for silicon as the best option for

substrate materials.

V. ACKNOWLEDGEMENTS

This work is supported by the Department of

Electronics and Communication Engineering and the

Department of Electrical and Instrumentation

Engineering of Sant Longowal Institute of Engineering

and Technology, Longowal, Punjab, by providing

access to High Frequency structural Simulator Software.

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September 2015

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[19] J.S. Moon and D. Gaskill, “Graphene: Its Fundamentals

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AUTHOR’S INFORMATION

Rajni Bala was born in Longowal. She obtained her

B.tech (Electronics and Communication Engineering)

from MIMIT Malout, PTU Jalandhar in 2010 & M.tech

in (Electronics and Communication Engineering) from

SLIET Longowal, Deemed University in 2012.

Presently she is pursuing P.hd (Research Scholar) in

Deptt. Electronics & Comm. Engg. from SLIET

Longowal, Deemed University. Her research interests

include Miniaturized Resonant THZ antenna. She is a

Associate Member of Institution of Engineers, India. She has published 2 research papers in International and

National journals and 15 research papers in National

and International conferences.

Dr. (Mrs.) Anupma Marwaha is associate professor in

Electronics and Communication Engineering

Department at SLIET Longowal, Distt. Sangrur,

Punjab. She did her B. E and M.Tech in Electronics &

Comm. Engg. in 1990 and 1992 respectively. She

completed her Ph. D. Degree in Electronics from Guru

Nanak Dev University, Amritsar in the year 2003 with

specialization in the field of ‘Design and Field Analysis of

Electromagnetic Devices by Finite Element Method with

applications to Communication Engg., Microwave and Antennas’.

She is a Life Member of ISTE, New Delhi and Member of

Institution of Engineers, India. She has more than 75 publications

to her credit in International and National Journals of repute. Her

continuing research interests primarily underpin the overarching

notion that there are many underutilized, yet powerful ways in

which electromagnetic phenomena may be exploited in the area of

bio-medical engineering and in microscale and nanoscale

structures atlarge