Air-Filled High-Efficiency W-Band Metasurface Antennas Using the Microcoaxial Additive Manufacturing Process

Millimeter-wave and terahertz antennas require high manufacturing precision and low dielectric loss. As a new solution, micrometal additive manufacturing (M-MAM) technology can achieve multilayer pure copper structure, with planar pattern precision of up to $5~\mu $ m. In this work, a new nine-layer M-MAM process flow was used to fabricate a W-band metasurface antenna. The large metal and blank areas of the antenna structure were substituted by periodic rectangular metal posts to balance the electrostatic field across the wafer during the electroforming process. These structural changes ensure the uniformity of the layer thickness and help reduce the accumulation of errors. The measured 10-dB impedance bandwidth of the antenna is 22.5%, and a maximum peak gain of 13.7 dBi is achieved in an overall aperture size of $1.43 \lambda _{0} \times 0.88 \lambda _{0}$ . In addition, the front-to-back ratio (FBR) of the metasurface antenna is larger than 20 dB across the whole bandwidth. Thanks to the M-MAM technology that nearly eliminates the dielectric loss, the antenna achieved a maximum simulated radiation efficiency of 96%.