A H-band Direct Laser Written Leaky-wave Fed GRIN Lens Antenna

Lens antennas are commonly used for communication and imaging applications in the terahertz band and are often fabricated from high-resistivity silicon due to its low dielectric loss. Drawbacks to silicon lens antennas are that they can be bulky, expensive and require specialized fabrication processes (e.g. DRIE). Additionally, silicon lens antennas are susceptible to Fresnel reflection losses and exhibit a strong FabryPerot response, primarily due to the high dielectric constant of silicon. A lower cost solution is to develop a polymeric lens antenna which can be fabricated using 3D printing processes. However, conventional 3D printing techniques (e.g. FDM and SLA) have limited resolution and cannot meet the fabrication tolerances required for operating frequencies above several hundred gigahertz. An alternate approach is to use Direct Laser Writing (DLW) based on Two-Photon Polymerization (2PP) of a photoresin (PR) which combines sub-micron fabrication accuracies with the ability to realize complex 3D geometries. A limitation of this approach is the typically high dielectric loss of the available PRs in the terahertz band.
In this work, we propose an H-band leaky-wave fed graded-index (GRIN) lens antenna fabricated using DLW-2PP of a PR. Figure 1 (left) illustrates the GRIN lens antenna design concept which is fabricated using the commercially available PR called IP-Q (Nanoscribe GmbH). At a frequency of 300 GHz, IP-Q has a measured loss tangent of 0.06 and a permittivity of 2.5. Compared to traditional lens antennas, the design presented in this work leverages leaky waves propagating in the air gap between the lens and the metal ground to illuminate the lens. This approach expands the field from the exciting WR3 waveguide in the transverse direction before the wavefront is reshaped by the lens. Dielectric losses are reduced due to the design's reduced dielectric filling factor compared to a conventional GRIN lens antenna.