Experimental Characterization of a New Active Huygens’ Metasurface-based Element for Beam Steerable Lens at Ka-Band

In this paper, a novel reconfigurable linearly polarized ultrathin unit cell design for lens applications at Ka-band frequencies (26-28.75 GHz) is presented. The proposed unit cell, comprising of two dislocated I-shaped metal strips with integrated varactor diodes on a single substrate, functions as a reconfigurable Huygens’ metasurface-based lens element with both electric and magnetic dipole resonances. The lens performance is further enhanced by adding interdigital parasitic strips between the I-shaped metal strips, which increase the capacitance and extend phase shift range. Additionally, an equivalent circuit model for the proposed Huygens’ metasurface-based unit cell is introduced to provide a clear understanding of the transmission mechanism. Based on this analysis, the proposed unit cell is fabricated and characterized in a specific waveguide simulator, allowing the validation of the design concept and ensure the performance of the varactor diode before proceeding with the full array fabrication. Experimental result demonstrates a broadband transmission phase shift with substantial tunability over a fractional bandwidth of 10%. The low loss performance of the proposed element makes it an attractive candidate for electronically steerable flat-lens antennas.