Reconfigurable Huygens’ Metasurface-Based Unit-Cell and Electronically Steerable Active Flat-Lens Antenna at the Ka-Band

This article introduces an innovative method for achieving 2-D beam steering in an active lens operating at the Ka-band (26.7–29.35 GHz). The study outlines a detailed procedure for designing, optimizing, fabricating, and characterizing an electronically steerable flat-lens antenna with continuous phase range capability, tailored specifically for linear polarization at the Ka-band. The novel design in this work eliminates the need for individual unit-cell control by using a technique that reduces the number of required bias lines. The active unit cell is based on a double-layer Huygens’ metasurface (HMTS) with an I-shaped resonator and includes a varactor diode, which is associated with two bias lines shared by neighboring unit cells. The unit cell achieves a phase range of up to 360°. The technology features a grid structure consisting of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12\times 12$ </tex-math></inline-formula> reconfigurable unit cells, each equipped with dual varactor diodes to precisely regulate the phase distribution of the radiated field across the antenna aperture. Experimental results demonstrate the prototype’s capability to scan pencil beams across a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50^{\circ } \times 50^{\circ }$ </tex-math></inline-formula> window in the E- and H-planes, achieving a maximum gain of 19 dBi at broadside and exhibiting a 3-dB fractional bandwidth of 9.45%. The 2-D beam steering for (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta 0$ </tex-math></inline-formula>, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi 0$ </tex-math></inline-formula>) = (−30°, −15°) is verified at 27.5 GHz, with a total efficiency for all scan angles ranging from 11% to 26.37%.