Overcoming the Diffraction Limit with a Planar Left-Handed Transmission-Line Lens

We report experimental results at 1.057 GHz that demonstrate the ability of a planar left-handed lens, with a relative refractive index of $-1$, to form images that overcome the diffraction limit. The left-handed lens is a planar slab consisting of a grid of printed metallic strips over a ground plane, loaded with series capacitors ($C$) and shunt inductors ($L$). The measured half-power beamwidth of the point-source image formed by the left-handed lens is 0.21 effective wavelengths, which is significantly narrower than that of the diffraction-limited image corresponding to 0.36 wavelengths.

Figure 1

Transmission line unit cells.

Figure 2

The left-handed planar transmission-line lens. The unit cell of the left-handed (loaded) grid is shown in the top inset, while the unit cell of the positive-refractive-index (unloaded) grid is shown in the bottom inset.

Figure 3

The measured vertical electric field detected 0.8 mm above the surface of the entire structure at 1.057 GHz. The plot has been normalized with respect to the source amplitude (linear scale).

Figure 4

The measured vertical electric field above row 0 at 1.057 GHz. The vertical dashed lines identify the source (column 0) and image (column 10) planes while the vertical solid lines identify the interfaces of the left-handed planar slab. The growth of the evanescent waves in the left-handed lens is clear.

Figure 5

The measured vertical electric field at the source (dashed curve) and the image (solid curve) planes along with the theoretical diffraction-limited patterns in a continuous medium (dash-dotted curve) and a periodic TL grid medium (triangles) as well as the computed loss-limited image (squares). The measured source and image peaks lie within 7% of each other but have been normalized to 1.