  Despite their great potential in communication and sensing applications,
printed leaky-wave antennas have rarely been reported at mm-wave frequencies.
In this paper, tapered leaky-wave antennas operating at 80 GHz are designed,
fabricated and experimentally characterized. While most continuous leaky-wave
antennas use subwavelength strips or other comparably small elements, in this
work, the surface impedance is discretized very coarsely using only three
square patches per period. With this architecture, a wide range of surface
reactance can be achieved while maintaining a minimum feature size of the
metallic pattern that is feasible for printed circuit fabrication. As the
analytical solution for the bandstructure of sinusoidally modulated reactance
surfaces is inaccurate for coarse discretization, we find it using full-wave
simulation. In order to control side lobes effectively, we use a tapered
aperture illumination according to the Taylor one-parameter distribution. A
comprehensive experimental demonstration is presented, including near-field and
far-field measurements. Therewith, we verify the designed aperture illumination
and we reveal the origin of spurious far-field features. Side lobes are
effectively suppressed and spurious radiation is reduced to -18 dB compared to
the main lobe.
