Planar THz electromagnetic graphene pass-band filter with low polarization and angle of incidence dependencies

We propose and analyze a graphene electromagnetic filter for the terahertz (THz) region. The filter represents a planar square array of graphene elements. A unit cell of the array is formed by two coaxial graphene rings placed on the opposite sides of a thin dielectric substrate. The two electromagnetically coupled rings resonate with dipole plasmonic modes. The rings have slightly different dimensions and consequently different yet close individual resonant frequencies. At a frequency lying between these two resonances, the currents in the two interacting rings have opposite directions. This leads to a suppression of the reflected from the array waves and consequently to a high transmission through the array. For the chemical potential of the graphene μ_c=0.6 eV, the calculated quality factor of this resonant mode is Q=5 at the frequency f=0.8  THz. At this frequency, the reflection coefficient of the array equals -36 dB and the transmission peak which is defined by the graphene losses is -1.8 dB. We show that the frequency position of the transmission peak can be varied in a wide range by the graphene chemical potential.