The THz antenna plays an important role in the ultra-broadband and secured data transfer in the wireless communication systems [27]. The characteristics of the graphene ring patch is designed and investigated in the frequency range varying from 0.6 to 0.7 THz, using the HFSS simulation tool and the performance is analyzed in term of Coefficient reflexion (S11), Gain (dB), Directivity (dBi) and Bandwidth (GHz).The bandwidth of a graphene based nano patch antenna using PBG substrate is higher than of a microstrip patch antenna with conventional material and normal substrate [28].
In the present work, the performance of graphene of four types of antennas on photonics crystal substrate have been proposed and simulated. The figure 8 present coefficient reflexion plot for the four proposed antenna with several types ground plane.
It is observed from Figure 8 that the modification of ground plane modified propagation of electromagnetic waves through dielectric substrate and can create a stop band at desired frequency. The operating frequencies the conventional antenna without PBG substrate and with whole ground plane vary in the range of 0.643–0.738 THz and they have the same S11=-15dB.
According to the figure 8, we notice that the four proposed antennas (1,2,3 and 4) don't resonate at frequency at 0.738 THz and offers the coefficient reflexion S11 ≤ −10 dB.
The electric field radiation properties of a graphene ribbon patch antenna (1) with EBG substrate are illustrated in figure 9.
For the proposed antenna (1), the partial ground plane creates a stop band in the conventional antenna which results in deletion of second resonant frequency hence the adaptation of antenna is enhanced at S11=-51dB at 0.659 THz.
The S11 configuration of the second patch antenna (2) is present in figure 8. It consists of a One-Dimensional Electromagnetic Band Gap (1-D EBG) structure with a partial PEC ground plane.
It is clear that coefficient reflexion has been decreased from -15dB to -26.27dB but the resonance frequency has shifted from 0.643THz to 0.672 THz.
Figure 10 presents the simulated E-plane and H-plane radiation pattern of antenna (2). We observed that secondary lobes are virtually inexistent and the beam width is around 30°.
The ground plane of the graphene ribbon patch antenna is partial so there is some back radiation and the beam peak is directional.
According to the graph of the figure 8 it can be seen that the antenna (3) -with the PBG structures and partially defected ground plane-resonates at 0.66 THz with S11=-41.76 dB and it covers the wide bandwidth of 10 GHz.
In this case, along E-field in Figure 11 which correspond to the radiation direct of defected ground plane, there is little power transmitted from the graphene ring patch antenna as comparedto the other antennas (1) and (2). The E-plane has an important role in this case because it’s determining the point of strongest signal.
For the proposed antenna (4), the holey ground plane with the PBG structures creates a stop band in the conventional antenna.
The second resonant frequency has disappeared and we notice a good adaptation of antenna (4). The S11 of this proposed patch antenna improves from -15 dB to -36.25 dB.
It can be observed that the 2D radiation pattern of the co-polarization has a null at θ=60°.The beam peak is directional
TABLE III
Comparison of parameters results of proposed antennas with four types of ground plane
Particular
|
fr
(THz)
|
S11
(dB)
|
Bw
(GHz)
|
Gain
(dB)
|
Directivity
(dB)
|
Conv. antenna
|
0.643-0.738
|
-15/ -15
|
9-9.5
|
7.77
|
6.24
|
Antenna (1)
|
0.659
|
-51.02
|
10
|
6.36
|
6.04
|
Antenna (2)
|
0.672
|
-26.27
|
20
|
6.32
|
6.09
|
Antenna (3)
|
0.660
|
-41.76
|
10
|
7.62
|
6.38
|
Antenna (4)
|
0.632
|
-36.25
|
11
|
3.53
|
3.99
|
at θ=-100°, radiating from the center ofthe patch and there is back radiation characterized by the front-to-back ratio.The main directivity was directed at the horizontal plane, whichformed a directional signal level in the E-plane.
TABLE IV
Comparison of proposed antennas with existing graphene based patch antenna.
Particular
|
fr(THz)
|
S11(dB)
|
Bw(GHz)
|
Gain(dB)
|
Directivity(dB)
|
Type of patch
|
Patch shape
|
PBP’s
structures
|
Type of ground plane
|
[29]
|
0.64–0.85
|
-35
|
/
|
/
|
5.6
|
Graphene
|
Rectangular ribbon patch antenna
|
Without
PBG
|
Whole ground plane
|
[30]
|
0.690
|
−34.9
|
24
|
6.86
|
7.01
|
Cuivre
|
Rectangular patch
|
With PBG
|
Defected ground plane
|
[31]
|
0.6308
|
-44.71
|
36.23
|
7.94
|
8.81
|
Cuivre
|
Microstrip patch
|
With PBG
|
Holey ground plane
|
[32]
|
0.703
|
-47.8
|
26.22
|
4.014
|
6.835
|
Graphene
|
Rectangular patch
|
With PBG
|
Defected ground plane
|
[33]
|
0.750
|
-36
|
/
|
5.09
|
5.71
|
Graphene
|
Rectangular patch
|
Without
PBG
|
Whole ground plane
|
Antenna (1)
|
0.659
|
-51.02
|
10
|
6.36
|
6.54
|
Graphene
|
Squareribbonpatch antenna
|
With PBG
|
Partial ground plane
|
Antenna (2)
|
0.672
|
-26.27
|
20
|
6.32
|
7.09
|
Partial ground plane + supertate
|
Antenna (3)
|
0.660
|
-41.76
|
10
|
7.62
|
6.38
|
Defected ground plane
|
Antenna (4)
|
0.632
|
-36.25
|
11
|
3.53
|
3.99
|
Holey ground plane
|
Table IV summarized the radiation performance of existing THz graphene antennas with the four proposed structure.
Analyzing the effects, the holey ground of antenna (4) causes a reduction in gain and directivity due to radiation loss. It can be observed from designs of antenna (1), antenna (2) and antenna (3) proposed that the gain and the directivity containing partial and defected ground plane improves. Maximum S11 is improved up to -51.02 dB, which is a good coefficient in the THz range and better than the work reported by [29], [30], [31] and [33].