Design and Characterization of a Sub-THz Lens Antenna Based on Customized Composite Materials

This paper describes the design, fabrication process, and operation of an extended hemispherical low-permittivity lens antenna for sub-terahertz (sub-THz) frequency bands to alleviate some of the performance limitations seen with high-permittivity (e.g., silicon) lenses. The proposed lens concept is intended to enhance the radiation characteristics of an on-chip antenna designed on a high-permittivity substrate: customized matching layers are placed between the low-permittivity lens and the source that provide a smooth permittivity transition (from high to low) towards the air interface to improve radiation characteristics and impedance matching. The permittivity of each matching layer and the lens is obtained using the theory of reflections at multiple interfaces. For proof of concept, the lens is illuminated with a WR-3.4 rectangular waveguide (RWG) that is placed at an optimized distance to obtain optimal impedance matching at 220–330 GHz and a high directivity (>22 dBi). By customizing the material and layer properties, the proposed lens concept can be made compatible with different semiconductor technologies. To verify the performed simulations, a prototype of the lens antenna was fabricated and measured, with a good agreement observed between both results. Additionally, a study was conducted to observe the beamsteering characteristics of the designed lens in the E- and H-plane. Results indicate beamsteering capability in the range of ±19∘–21∘ with a maximum scan loss of 5.5 and 4.5 dB in the E- and H-plane, respectively.