  In this paper, we analytically design a simple configuration of a broadband
THz and polarization-insensitive absorber. The mentioned absorber consists of
two layers of graphene disks, and the transmission line model is considered for
the whole of the proposed absorber's structure to design it accurately.
Therefore, the input admittance of the designed absorber is obtained by the
transmission line model. Also, the real part of the input admittance is
approximately tuned to be matched to the free space admittance. In contrast,
the imaginary part of it is closely adjusted to zero around the central
frequency of the THz absorber. Using only just two layers of Periodic Arrays of
Graphene Disks (PAGDs) with one kind of dielectric as the material of
substrates, it causes that the absorption of the structure can be achieved
higher than 90% by the Finite Element Method (FEM). Normalized bandwidth has
reached up to 75.4% in 5 THz as the central frequency of the device. As the
next step, we use the CST studio software to validate our designed absorber,
and it will show that the numerical results will have the best matching with
the analytical method.
