Wideband Planar Transmission Line Hyperbolic Metamaterial for Subwavelength Focusing and Resolution

We analyze both theoretically and experimentally subwavelength focusing by using a planar hyperbolic metamaterial (HM) at microwave frequencies. The proposed HM consists of microstrip transmission lines (TLs) loaded by lumped components and exhibits a very flat wave vector iso-frequency dispersion diagram over a wide frequency range, and thus able to transport spectral component with large wavenumbers. This flatness is here exploited to provide subwavelength focusing with a full width half maximum (3-dB power width) of about λ_g/31 and λ_g/19 at 0.5 and 1 GHz, respectively, where λ_g is the guided wavelength in the TL microtrip grid. Numerical simulation results are in good agreement with measurement ones. Moreover, we also investigate the capability of the proposed HM to resolve sources with subwavelength distance of about λ_g/6 and λ_g/3 at 0.5 and 1 GHz, respectively.