Ijecet 06 09_005

1. http://www.iaeme.com/IJECET/index.asp 39 editor@iaeme.com
International Journal of Electronics and Communication Engineering & Technology
(IJECET)
Volume 6, Issue 9, Sep 2015, pp. 39-47, Article ID: IJECET_06_09_005
Available online at
http://www.iaeme.com/IJECETissues.asp?JTypeIJECET&VType=6&IType=9
ISSN Print: 0976-6464 and ISSN Online: 0976-6472
© IAEME Publication
DESIGN AND PERFORMANCE
INVESTIGATION OF TUNABLE UWB THZ
ANTENNA BASED ON GRAPHENE
FRACTAL ARTIFICIAL MAGNETIC
CONDUCTOR
Hussein A. Abdulnabi and Riffat T. Hussiein
Department of Electrical Engineering, University of Technology, Baghdad, Iraq
Raad S. Fyath
Department of Computer Engineering, AL-Nahrain University Baghdad, Iraq
ABSTRACT
In this paper a tunable antenna using graphene-based fractal shape
artificial magnetic conductor (AMC) is proposed for ultra-wideband (UWB)
terahertz (THz) application. The resonance frequency of the proposed antenna
can be tuned by varying the applied DC voltage which leads to variation in
chemical potential of graphene. The antenna consists of a bowtie shaped patch
mounted on 15x15 graphene patches based on new fractal shape AMC unit. It
is observed that the resonance frequency and the bandwidth increase by
increasing the applied voltage.
Key words: Graphene, Artificial magnetic conductor, Terahertz antenna
Cite this Article: Hussein A. Abdulnabi, Riffat T. Hussiein and Raad S.
Fyath. Design and Performance Investigation of Tunable UWB THZ Antenna
Based on Graphene Fractal Artificial Magnetic Conductor, International
Journal of Electronics and Communication Engineering & Technology, 6(9),
2015, pp. 39-47.
http://www.iaeme.com/IJECET/issues.asp?JTypeIJECET&VType=6&IType=9
1. INTRODUCTION
Graphene has been named the simplest complex material. Graphene has drawn
attention due to its unique properties and advantages and it is used in many
application including electrical, thermal, and mechanical applications [1-3]. The
surface conductivity of the graphene can be varied by varying applied electrical
voltage [4-6], thus many graphene-based devices such as antennas, filters, absorbers

2. Hussein A. Abdulnabi, Riffat T. Hussiein and Raad S. Fyath
http://www.iaeme.com/IJECET/index.asp 40 editor@iaeme.com
and polarizer's have been proposed for band in microwave, THz and optical
frequencies [7-12].
The graphene can be used to design THz antennas, as radiating part [17-19],
parasitic component, or high impedance surfaces (HIS) [20-22]. High impedance
surface is a planar array of periodic surface which can enable the manipulation of
electromagnetic wave propagation. Thus this structures has been widely used in the
design of some antennas such as low profile leaky wave antenna operating at
microwave regime with high gain and efficiency in comparison with conventional
ground plane. Also adding active HIS elements loaded with varactor diodes to the
antennas enables efficient beam steering and easy frequency tuning [23-26]. It is also
possible to insert periodic graphene patches as antenna ground.
It has been shown that the reflection, absorption and polarization of graphene can
be controlled by varying external applied electric biased DC voltage [7]. In [21], a
graphene biased switchable HIS in the THz band has proposed for getting beam
steering.
The graphene biased reflective array has been applied for the antenna to get
frequency tuning and beam reconfiguration [17] and [22]. In this paper a novel
tunable antenna based on a new fractal shape of graphene AMC is proposed. The
applied voltage is used to tune this antenna in order to wide its bandwidth.
2. THEORETICAL BACKGROUND
2.1. GRAPHENE CONDUCTIVITY
The graphene can modeled as an infinitesimally thin surface which is characterized by
surface conductivity σ(ω,τ,µc,T ). The Drude model of graphene conductivity in
intraband can be written by [27]
σs(ω)= (1)
where ω is the angular frequency, τ is the scattering time , μc is the chemical
potential in eV, which can be controlled by chemical doping or by applying a bias
voltage, T is the absolute temperature, e is the electron charge, ħ is reduced
Planck’s constant, and kB is Boltzmann's constant.
The surface impedance of graphene can be expressed
Zs(ω) = 1/σs(ω) (2)
3. GRAPHENE-BASED AMC
The graphene is used as AMC unit cell which consists of a periodic of square patches
with dimensions D and the gap between adjacent patches g as shown in Fig(1) [27].

3. Design and Performance Investigation of Tunable UWB THZ Antenna Based on Graphene
Fractal Artificial Magnetic Conductor
http://www.iaeme.com/IJECET/index.asp 41 editor@iaeme.com
(a) (b)
Figure 1 (a) AMC unit cell (b) AMC graphene patches array.
The surface impedance of the patch array at THz band can be approximated by
[28]
Zg = j = (3)
where Cg represents the capacitance between adjacent graphene patches and
Ceff = εo (εr+1) D ln (4)
Here εo is the permittivity of free space, εr is the relative permittivity of the
substrate, and Ceff is the effective capacitance related to the patch geometry and
background environment.
The circuit model representing the equivalent circuit of graphene patches array
mounted on grounded substrate is shown in Fig. (2) [28].
Figure 2 The equivalent circuit model of the AMC surface [28].
The impedance of grounded transmission line can be expressed as

4. Hussein A. Abdulnabi, Riffat T. Hussiein and Raad S. Fyath
http://www.iaeme.com/IJECET/index.asp 42 editor@iaeme.com
Zd = jηo tan (kd h) / (5)
kd = ω (6)
where ηo is the wave impedance in free space, h is the substrate thickness, kd is the
wave number of the incident wave, and Ld represent the inductance of the grounded
substrate.
The total impedance is the parallel combination of Zd and Zg The reflection
magnitude of the incident wave can be computed as
R = (Zs - ηo) / (Zs+ ηo) (7)
The resonance frequency of AMC surface can be expressed as
ωo = 1/ (8)
4. PROPOSED ANTENNA
The proposed antenna is based on HIS and composed of array of periodic fractal
conductive graphene sheets [29]. Each sheet of graphene is formed to new shape, see
Fig. 3.
(a) 1st
iteration (b) 2nd
iteration (c) 3rd
iteration
Figure 3 Generation of fractal patch of graphene AMC.
Wpn = (3/4)n
Wp (9)
Lpn = (1/4)n
Lp (10)
where Wp and Lp are the width and length of initiator, respectively
A simple bowtie antenna made of gold is placed above the graphene-based AMC
ground plane, as shown in Figs. 4(a) and (b). A 10 um-thick grounded SiO2 is
employed as the AMC substrate. In consideration of the feasibility in fabrication, a
300 um-thick silicon handle wafer is bounded under the quartz substrate. Above the
quartz is a 50 nm-thick polycrystalline silicon layer and 10 nm-thick Al2O3 film in
sequence, which can be easily obtained by RF sputtering [27].
The AMC ground plane consists of 15 x 15 graphene fractal shape patches with D
= 10 um and g =1um. The graphene patches can be connected by 60 nm-wide
graphene nano- ribbons to keep all patches at the same µc when applying a DC
voltage between the AMC and polycrystalline silicon. A 2 um-thick SiO2 is deposited
on graphene-based AMC, and the gold bow-tie antenna can be finally placed on Sio2

5. Design and Performance Investigation of Tunable UWB THZ Antenna Based on Graphene
Fractal Artificial Magnetic Conductor
http://www.iaeme.com/IJECET/index.asp 43 editor@iaeme.com
layer method [27]. The detailed antenna structure with proposed fractal patches of
graphene AMC is illustrated in Fig (4) using CST environment.
(b) Top view
(c) Schematic of the proposed fractal patch of periodic AMC unit cells in CST environment.
Figure 4 Antenna structure with proposed AMC
w2
L
W1

6. Hussein A. Abdulnabi, Riffat T. Hussiein and Raad S. Fyath
http://www.iaeme.com/IJECET/index.asp 44 editor@iaeme.com
5. RESULTS
Simulation results are obtained using CST studio 2014 for two value of chemical
potential µc1and 0.4 eV. Fig. (5) shows scattering parameter S11 in dB of the
proposed antenna for µc = 1eV . The resonance frequency is 2.9 THZ and the
operating frequency bands are (2.4-3.1) THz and (3.5- 5) THz
Figure 5 S11 of the proposed antenna at 1eV chemical potential
The gain of the antenna at frequency 2.5THz is given in Fig. (6). the maximum gain at
this frequency is 6.59 dB.
Figure 6 Gain of the antenna at frequency 2.5THz
Figure (7) shows S11 in dB of the proposed antenna when µc = 0.4. Many
resonance frequencies appear at (2, 2.75, 3.4, and 4) THz and the operating frequency
bands are (1.8 - 2.2) THz and are (2.75 - 5) THz
Figure 7 S11 of the proposed antenna at 0.4eV chemical potential.
Figures (8) and (9) show the gain of the antenna at frequency 1.5THz in polar and
in 3D representations, respectively when µc = 0.4eV. The maximum gain at this
frequency equals to 2.46 dB

7. Design and Performance Investigation of Tunable UWB THZ Antenna Based on Graphene
Fractal Artificial Magnetic Conductor
http://www.iaeme.com/IJECET/index.asp 45 editor@iaeme.com
Figure 8 Gain of the proposed antenna in polar representation at 1.5 THz when µc = 0.4eV.
Figure 9 Gain of the proposed antenna in 3D representation at 1.5 THz when µc = 0.4eV.
CONCLUSIONS
In this paper a new graphene fractal shape- based AMC antenna has been designed. A
bowtie antenna has been mounted over graphene fractal AMC array and the tunability
of graphene is demonstrated by changing the chemical potential. It is shown that both
the bandwidth and the resonance frequency increase by increasing the chemical
potential. Further, the fractal shape of graphene AMC unit leads to multiband antenna
and many resonance frequencies.
REFERENCES
[1] A. K. Geim and K. S. Novoselov, The rise of graphene, Nature Mat., 6(3), Apr.
2007, pp. 183–191.
A. K. Geim. Graphene: Status and prospects, Science, 324(5934), Jun. 2009, pp.
1530–1534,
[2] A. N. Grigorenko, M. Polini, and K. S. Novoselov. Graphene plasmonics, Nature
Photon., 2012, 487, pp. 749–758.
[3] B. Sensale - Rodr´ıguez, R. Yan, L. Liu, D. Jena, and H. G. Xing. Graphene for
reconfigurable terahertz optoelectronics, Proc. IEEE, 101(7), Jul. 2013, pp.
1705–1716.
[4] Y. R. Padooru, A. B. Yakovlev, C. S. R. Kaipa, G. W. Hanson, F. Medina, and F.
Mesa. Dual capacitive-inductive nature of periodic graphene patches:
Transmission characteristics at low-terahertz frequencies, Phys. Rev. B, 87, article
no. 115401, Mar. 2013.

8. Hussein A. Abdulnabi, Riffat T. Hussiein and Raad S. Fyath
http://www.iaeme.com/IJECET/index.asp 46 editor@iaeme.com
[5] T. Low and P. Avouris, Graphene plasmonics for terahertz to mid-infrared
applications, ACS Nano, 8(2), 2014, pp. 1086–1101.
[6] A. Fallahi and J. Perruisseau-Carrier, Design of tunable biperiodic graphene
metasurfaces, Phys. Rev. B, 86, article no. 195408, Nov. 2012.
[7] F. Rano. Graphene terahertz plasmon oscillators, IEEE Trans. Nanotechnol. 7(1),
Jan. 2008, pp. 91–99.
[8] J. T. Kim and C- G. Choi. Graphene-based polymer waveguide polarizer, Opt.
Exp., 29(4), pp. Feb. 2012, 3556–3562.
[9] B. Gulbahar and O. B. Akan. A communication theoretical modeling of single-
layer graphene photodetectors and efficient multireceiver diversity combing,
IEEE Trans. Nanotechnol., 11(3), May 2012, pp. 601–610.
[10] B. Z. Xu, C. Q. Gu, Z. Li, and Z. Y.Niu, A novel structure for tunable terahertz
absorber based on grapheme, Opt. Exp., 21(20), Oct. 2013, pp. 23803–23811.
[11] A. Andryieuski and A. V. Lavrinenko. Graphene metamaterials based tunable
terahertz absorber: Effective surface conductivity approach, Opt. Exp., 21(7),
Apr. 2013, pp. 9144–9155.
[12] B. Wu, H. M. Tuncer, M. Naeem, B. Yang, M. T. Cole, W. I. Milne, and Y. Hao,
Experimental demonstration of a transparent graphene millimeter wave absorber
with 28% fractional bandwidth at 140 GHz, Sci. Rep., 4, article no. 4130, Feb.
2014.
[13] Y. Yao, M. A. Kats, P. Genevet, N. Yu, Y. Song, J. Kong, and F. Capasso. Broad
electrical tuning of graphene-loaded plasmonic antennas. Nano Lett., 13(3), Feb.
2013, pp. 1257–1264.
[14] R. Filter, M. Farhat, M. Steglich, R. Alaee, C. Rockstuhl, and F. Lederer. Tunable
graphene antennas for selective enhancement of THz-emission, Opt. Exp., 21(3),
Feb. 2013, pp. 3737–3745.
[15] H. J. Xu,W. B. Lu, Y. Jiang, and Z. G. Dong. Beam-scattering planar lens based
on grapheme, Appl. Phys. Lett., 100(5), p. article no.051903, 2012.
[16] M. Esquius-Morote, J. S. G´omez-D´ıaz, and J. Perruisseau-Carrier. Sinusoidally
modulated graphene leaky-wave antenna for electronic beamscattering at THz,
IEEE Trans. Terahertz Sci. Technol., 4(1), Jan. 2014, pp. 116–122.
[17] E. Carraso and J. P. Carrier. Reflectarray antenna at terahertz using grapheme,
IEEE Antennas Wireless Propag. Lett, 12, pp. 253–256, 2013.
[18] M. Tamagnone, J. S. G´omez-D´ıaz, J. R. Mosig, and J. Perruisseau-Carrier,
Analysis and design of terahertz antennas based on plasmonic resonant graphene
sheets, J. Appl. Phys., 112(11),article no. 114–915, 2012.
[19] M. Dragoman, A. A. Muller, D. Dragoman, F. Coccetti, and R. Plana. Terahertz
antenna based on grapheme, J. Appl. Phys., 107(100), p. 104 313, 2010.
[20] Y. Huang, L. S.Wu,M.Tang, and J.Mao. Design of a beam reconfigurable THz
antenna with graphene-based switchable high-impedance surface, IEEE Trans.
Nanotechnol., 11(4), Jul. 2012, pp. 836–842.
[21] M. Tamagnone, J. S. Gomez Diaz, J. Mosig, and J. Perruisseau-Carrier, Hybrid
graphene-metal reconfigurable terahertz antenna, in Proc. Int. Microw. Symp,
Seattle, WA, USA, Jun. 2013, pp. 1–3.
[22] R. Guzman-Quiros, J. L. Gomez-Tornero, A. R. Weily, and Y. J. Guo.
Electronically steerable 1-D Fabry-Perot leaky-wave antenna employing a
tunable high impedance surface, IEEE Trans. Antennas Propag, 60(11), Nov.
2012, pp. 5046–5055.

9. Design and Performance Investigation of Tunable UWB THZ Antenna Based on Graphene
Fractal Artificial Magnetic Conductor
http://www.iaeme.com/IJECET/index.asp 47 editor@iaeme.com
[23] F. Costa and A. Monorchio. Design of subwavelength tunable and steerable
fabry-perot/leaky wave antennas, Prog. Electromagn Res, 111, pp. 467–481,
2011.
[24] D. F. Sievenpiper, J. H. Schaffner, R. Loo, G. Tangonan, S. Ontiveros, and R.
Harold. A tunable impedance surface performing as a reconfigurable beam
steering reflector, IEEE Trans. Antennas Propag., 50(3), Mar. 2002, pp. 384–
390,.
[25] D. F. Sievenpiper, J. H. Schaffner, H. Song, R. Y. Loo, and G. Tangonan. Two-
dimensional beam steering using an electrically tunable impedance surface, IEEE
Trans. Antennas Propag., 51(10), Oct. 2003, pp. 2713–2722.
[26] X. C. Wang, W. S. Zhao, J. Hu, and T. Zhang. A novel tunable antenna at THz
frequencies using graphene-based artificial magnetic conductor (AMC), Prog.
Electromagn. Res. Lett., 41, May. 2013, pp. 29–38.
[27] X. C. Wang, W. -Y. Li, W.-S.Zhao, J. Hu, comparative study on graphene –based
artificial magnetic conductor (AMC), PIERS proceedings, Sweden, Aug. 2013,
pp. 496-499.
[28] Riffat T. Hussien, Dheif I.Abood. A wideband hybrid plasmonic fractal patch
nanoantenna. IJECET, 5, Sep. 2014, pp. 1-8.
[29] Ayad Shohdy W. Ghattas and Elsayed Esam M. Khaled. A Compact Proximity–
Fed Quad Band–Notched Ultra–Wideband Patch Antenna, International Journal
of Electronics and Communication Engineering & Technology, 5(1), 2015, pp. 43
– 51.
[30] Dr. Nagraj K. Kulkarni. A Comparative Study of Various Patch Antennas For
Wlan Applications, International Journal of Electronics and Communication
Engineering & Technology, 5(1), 2015, pp. 182 - 186