Terahertz Planar Cavity Antenna Based on Effective Medium for Wireless Communications

Terahertz sources require compact lenses for efficient outcoupling and manipulation of terahertz waves. Traditional terahertz lenses are bulky and require high-precision fabrication techniques such as micromachining, which limit their flexibility in integrated systems. As an alternative, we present a planar high-gain cavity antenna integrated with a waveguide feed. The antenna is made by laser-etching of high-resistivity float-zone silicon to create non-uniform hole arrays, which function as gradient-index (GRIN) lenses for beamforming. To address the insufficient phase coverage range caused by limitations in feasible etching depth and the intrinsically tapered side walls of the holes, direct laser-etching is performed on both sides of the silicon wafer. A cyclic olefin copolymer (COC) sheet is placed on top of the silicon wafer to aid silicon-air impedance matching. The silicon cavity antenna is experimentally validated, with results confirming that a maximum broadside gain of 19 dBi can be achieved at the center frequency of 275 GHz, with a 3-dB bandwidth of around 29%. We further demonstrate that such a high-gain antenna is applicable to error-free point-to-point short-range wireless signal transmission. A demonstration of uncompressed 4K-resolution video transmission is also included. The proposed planar antenna design has the advantages of a significantly reduced device profile and is a cost-effective solution for future practical array-level designs.