  Focusing using conventional lenses relies on the collection and interference
of propagating waves, but discounts the evanescent waves that decay rapidly
from the source. Since these evanescent waves contain the finest details of the
source, the image suffers a loss of resolution and is referred to as
'diffraction-limited'. Superlensing is the ability to create an image with fine
features beyond the diffraction limit, and can be achieved with a
'Veselago-Pendry' lens made from a metamaterial. Such a Veselago-Pendry
superlens for imaging in free space must be stringently designed to restore
both propagating and evanescent waves, but meeting these design conditions
(isotropic n = epsilon_r = mu_r = -1) has proven difficult and has made its
realization elusive. We demonstrate free-space imaging with a resolution over
three times better than the diffraction limit at microwave frequencies using a
Veselago-Pendry metamaterial superlens based on the negative-refractive-index
transmission-line (NRI-TL) approach, which affords precise control over its
electromagnetic properties and is also less susceptible to losses than other
approaches. A microwave superlens can be particularly useful for illumination
and discrimination of closely spaced buried objects over practical distances by
way of back-scattering, e.g. in tumour or landmine detection, or for targeted
irradiation/hyperthermia.
