Structure of graphene-gold based antenna is shown in Fig. 1. As it is obvious from the figure, in the structure of the antenna, a triangular and square scheme of gold has been worked. According to the known rules, one of the methods of creating and achieving circular polarization is to create sectors at the edges of the square-shaped patch. This is the working approach in the upcoming research. The difference is that in the square patch, the diagonal edges are only away from the center. Each of the sections marked in the figure presents a different chemical potential in various states.
In this way, by turning off and on the \({\mu }_{c}\) of each slice, different polarizations are obtained. Chemical potential has two states: on (0.6 eV) and off (0 eV). In order to achieve right-handed circular polarization, the executive approach is that the chemical potential of parts 1 and 2 with DC bias level settings is equal to 0.6 eV, and at the same time, the chemical potential of part 3 is considered off or in other words 0 eV. To create and access left-handed circular polarization, the chemical potential of sections 1 and 3 should be considered to be on or 0.6 eV at the same time with the help of DC bias level settings, and at the same time, the chemical potential of section 2 should be turned off or considered 0 eV. And finally, to achieve linear polarization, the chemical potential of sections 1, 2, and 3 should be considered on or 0.6 eV at the same time. With the purpose of implement the goal of tuning the Fermi energy, which leads to adjusting the chemical potential; A 50 nm pad of polysilicon is considered in the lower part of the graphene layers. That changes in DC bias lead to changes in \({\mu }_{c}\). Also, a small distance between graphene sections is considered. While the main reason for this should be found in the DC bias independence of the parts. And even the final current distribution of the proposed structure is not affected by this. Referring to Eq. (3), maximum applied DC voltage of graphene layers is less than 75 volts. Sizes of the designed graphene-gold based antenna are demonstrated in Table 1. The whole configuration of the antenna is designed on a SiO2 substrate\(({\epsilon }_{r}=3.8)\). And the whole set is mounted on the ground plane.
Table 1
The physical sizes of the designed graphene-gold based antenna (µm)
Lx=Ly
|
L1 = L2
|
Lf
|
Wf
|
h (sub thickness)
|
D1
|
D2
|
S1
|
S2
|
190
|
47
|
31
|
11
|
35
|
6.8
|
5.5
|
10.2
|
5.3
|
The return loss of graphene-gold based antenna for all polarization conditions is displayed in Fig. 2. According to the rules, we know that the return loss in the matching output is generally acceptable if it is more than 10 dB in the microstrip antenna. In Fig. 3, the sweep return loss results for RHCP are selected for reporting among three polarization modes. Chemical potential changes from 0.5 eV to 0.7 eV have been reported. The chemical potential of the designed structure is 0.6 eV. According to the outputs of Fig. 3, it can be seen that with the increase of the chemical potential, the return loss results shift to the right and the height of the return loss peak decreases.
The results of axial ratio and radiation efficiency are evident in Fig.s 4 and 5. According to the radiation efficiency outputs in Fig. 5, it is clear that the negative consequence of gathering three different forms of polarization while maintaining the physical configuration of the structure is the reduction of radiation efficiency. The main goal of the work is the application of graphene for polarization adjusting. Therefore, optimizing all the elements of the antenna by applying the desired goals is contradictory in some cases. In the continuation of the discussion, the far field radiation pattern outputs for all types of polarization are discussed in separate sections.