Griffith, A. Kuz, C. O'Dell, S.

Oshchepkov, V. Sherlock, H. Suto, P. Wennberg, D. Wunch, T. Yokota, Y. Large format antenna coupled micorwave kinetic iinductance detector arrays for radioastronomy Andrey M. Phase locking a 4. Demonstration of an NEP of 3. Phase-locking of a 3. THz demonstration of the leaky lens antenna A. Galli, O.

Landgraf, P. Tol, I. Terahertz wavefronts measured using the Hartmann sensor principle M. Cui, J. Hovenier, Y. Ren, A. Polo, J. Development of a passive stand-off imager using MKID technology for security and biomedical applications C. Veefkind, I. Aben, K. McMullan, H. Otter, J. Claas, H. Eskes, J. Kleipool, M. Hasekamp, R. Hoogeveen, J. Landgraf, R. Snel, P. Tol, P. Ingmann, R. Voors, B. Kruizinga, R. Vink, H. Visser, P. Carbon monoxide from shortwave infrared reflectance measurements: A new retrieval approach for clear sky and partially cloudy atmospheres J.

Vidot, J. The analysis is made using the two-dimensional method of moments MoM 2D with surface impedance [ 15 , 16 ]. It was calculated by input impedance, reflection coefficient, and bandwidth from antennas with different geometrical parameters and values of chemical potential in the range of 0.

Some results were obtained by finite element method FEM with the Comsol software for comparison [ 17 ]. Figure 1 shows the geometry of the proposed broadband graphene antenna. This antenna is composed of two elements: a rectangular planar dipole with dimensions L and W , with same values used in [ 13 ] for comparison, and a circular passive ring or circular loop with inner radius R1 and outer radius R2. In other words, here we use an equivalent effective permittivity for the whole medium, which is considered homogeneous with no substrate.

The two elements are separated by a height H , as shown in Figure 1. Geometry of the rectangular planar dipole graphene coupled to a circular-loop antenna of the same material: a top view and b side view. The size of the dipole graphene has only one planar dimension e. This antenna is fed by an equivalent ideal voltage source called photomixer [ 13 ] with width W and gap length G in the middle of the dipole shown in Figure 1.

In this section, the model used for the surface conductivity of graphene, a summary of the MoM-2D model used in the analysis, and details of the Comsol model are presented. The experimental results show that edge effects on the graphene conductivity can be disregarded in the micrometer scale [ 15 ]. Therefore, one can use the electrical conductivity model developed for infinite graphene sheet. In this chapter, we use the Drude model for graphene surface conductivity in the range of 0.

The scattered field is. The numerical solution of Eq. With this approximation, we transform the integral Eq. The Comsol software [ 17 ], which is based on the finite element method, was used to simulate examples of graphene antennas to compare our MoM model. In this model, the dipole is excited by a voltage source with a lumped port element. In this section, we first present the results of two examples of conventional graphene dipole with different sizes. The principal characteristics of this antenna are reviewed. After that, we present the results for the broadband graphene dipole loop.

In this case, we analyze the dependence of the radiation and broadband properties of this antenna as a function of the geometry and chemical potential of the loop. For comparison of our models, this section presents the analysis of the two graphene antennas of the study [ 13 ]. The parameters of these antennas are presented in Table 1 , where we named them Antennas 1 and 2. These two antennas were simulated by MoM and Comsol.

The discretization details used in these models are shown in Figure 3 , where Figure 3a and b show the meshes used in the MoM method and Figure 3c and d show the meshes used in the FEM. Discretization mesh of graphene antenna used in simulations. The input impedance obtained for both antennas is presented in Figure 4 and the results of input resistance Rin and input reactance Xin between MoM, simulation Comsol and data from [ 12 ] are compared.

In general, a good agreement of the results is observed in these figures; the little differences are due to the differences in models and discretizations. The values of these resonant frequencies are presented in Table 2. Antenna 1 possesses a smaller length L than Antenna 2 but the resonances of Antenna 2 are higher than those of Antenna 1; this occur because the chemical potential of Antenna 2 is higher than that of Antenna 1 and this parameter shifts the input impedance to higher frequencies.

These results show that conventional graphene dipoles possess a smaller bandwidth. The next sections present the analysis of broadband graphene dipoles with bandwidths higher than those presented in this section. In this section, we present the numerical results for the broadband graphene dipole-loop antennas of Figure 1. First, we make a parametric analysis of geometry and then the effect of chemical potential of loop on the bandwidth and radiation characteristics. The results presented are input impedance, reflections coefficient, bandwidth, and radiation diagram.

A parametric analysis of graphene dipole loop of Figure 1 is presented in this section. In all the analysis, we fixed the size and chemical potential of the dipole with those values of Antennas 1 presented in Table 1. In addition, we varied the following parameters of loop element: inner radius R1, outer radius R2, and distance H. A total of simulations were done with the MoM code developed.

For each simulation, we plot the input impedance Zin of the antenna. First, we noted that for higher values of H and R1, the electromagnetic coupling between the dipole and the loop element is smaller. The geometries for some of these cases are presented in Figure 5d — f. Figure 4.

## Terahertz (THz) wireless systems for space applications - IEEE Conference Publication

Figure 5. High Gain CP Graphene-Based Reflectarray Previously, we have proposed a graphene metasurface which has prominent focusing capability in a wide-band of 1. Figure 6. Figure 7. Figure 8. Figure 9. Conclusions We have systematically investigated the spectral responses of graphene-based PB phase unit-cell and demonstrated a practical implementation of wide-band high gain CP reflectarray based on this configuration in the THz regime. Author Contributions L. Conflicts of Interest The authors declare no conflict of interest. References 1. Petrov V. Interference and SINR in millimeter waveand terahertz communication systems with blocking and directional antennas.

- Terahertz Antenna Technology for Space Applications.
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## Terahertz Antenna Technology for Space Applications

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