Reconfigurable metasurfaces, planar surfaces of subwavelength elements, offer dynamic control over electromagnetic wave properties. This research focuses on integrating two crucial functions: polarization conversion (switching the polarization state of an electromagnetic wave) and beam scanning (steering the wave's direction). These functionalities are essential for enhancing various applications, including image sensing, high-resolution imaging, radar systems, and communication efficiency, especially in scenarios involving multiple polarization states or non-line-of-sight propagation. Existing methods for achieving these functionalities often rely on electrical, thermal, or mechanical adjustments to modify the phase and amplitude of an array of radiofrequency (RF) elements using phase or spacing modulation. Phase modulation alters the wave-shifting function by changing conductivity or geometry, while spacing modulation adjusts the distance between elements to manipulate the wave direction. While many integrated designs exist, they are often limited by narrow scanning ranges, frequency dependence, and the inability to independently control both functions. This paper addresses these limitations by proposing a novel design that employs both rotation and scissor actuators to independently control polarization conversion and beam scanning within a transmissive metasurface.

The literature extensively discusses reconfigurable metasurfaces capable of polarization conversion and beam scanning. Many studies demonstrate impressive control over polarization states and beam angles, even suggesting the possibility of human-mind-based manipulation. However, the simultaneous integration of both polarization conversion and beam scanning, particularly with independent control, remains a challenge. Existing approaches struggle with narrow scanning ranges, frequency limitations, and the inability to independently control each function. This work aims to overcome these limitations.

The proposed metasurface comprises four distinct unit cells (UCs) arranged in a 12x12 array. Rotation actuators allow the UCs to rotate, switching between two different phase distributions for polarization conversion. A scissor actuator enables linear adjustment of the distance between UCs, facilitating beam scanning. The design leverages space modulation, where the distance between UCs determines the beam angle. The array factor (AF) formula, AF(θ) = Σ_{n=1}^{N} e^{j(n-1)d(θ)+jφ_n}, models beam steering, with *d* representing the spacing between UCs and φ representing the phase. Analytical modeling predicts a beam scanning range from 18° to 60°. Numerical simulations, performed using ANSYS Electronic High Frequency Simulation Software (HFSS), optimized the UC design (three layers of an I-shaped frequency selective surface on an FR4 substrate) to achieve polarization conversion and beam scanning. Simulations investigated the effects of UC rotation angle and spacing on beam steering for two modes (M1 and M2), each exhibiting different phase distributions for polarization conversion. The metasurface's performance was experimentally validated using a fabricated 12 × 12 array of UCs on a printed circuit board. Measurements using horn antennas at various UC spacings (d = 0.35λ, 0.50λ, 0.60λ) and modes (M1 and M2) verified the beam scanning and polarization conversion capabilities. An Anritsu MS2038C vector network analyzer recorded the radiation patterns.

Analytical calculations, based on the array factor formula, predicted a beam scanning range between 18° and 60°. Numerical simulations using HFSS confirmed the ability of the metasurface to independently control beam scanning and polarization conversion. For both polarization modes (M1 and M2), simulations showed a beam scanning range of approximately 28°. Experimental measurements validated these findings, showing good agreement between simulation and experimental results. The measured beam scanning angle was approximately 37° and 22° for UC spacings of 0.35λ and 0.60λ, respectively, which, while slightly different than the simulated 28°, demonstrates that the overall functionality of independent beam scanning and polarization conversion is achievable with this design. A slight discrepancy of 1° was observed for the RHCP wave at mode M1 with a UC spacing of 0.50λ, which can be attributed to fabrication tolerances. The metasurface operated effectively at 10.5 GHz with a bandwidth ranging from 10.15 to 10.65 GHz, achieving an average power ratio of >-2 dB and a transmission loss of -3.3 dB at a UC rotation angle of 30°. The simulation also showed that the transmission coefficient at 10.5 GHz decreased from -1.8 dB to -4.1 dB as the incidence angle increased from 0° to 25°.

The results demonstrate successful integration of independent beam scanning and polarization conversion functionalities within a single transmissive metasurface. The use of scissor and rotation actuators allows for independent control of these functions, addressing the limitations of previous designs. The close agreement between simulated and measured results validates the design's effectiveness. The achieved beam scanning range is significant and suitable for various applications. The methodology presented offers a practical and efficient approach to designing and fabricating multi-functional reconfigurable metasurfaces. The relatively slow tuning speed compared to electrical control might be a limitation in some high-speed applications; however, it is suitable for applications where fast tuning is not critical, such as biosensing, wireless power transmission, and indoor communication devices.

This research successfully demonstrated a reconfigurable transmissive metasurface capable of independent beam scanning and polarization conversion using scissor and rotation actuators. The achieved 28° beam scanning range at 10.5 GHz and the independent control of both functions represent a significant advancement in metasurface design. Future research could explore the use of lower-loss materials to improve transmission efficiency and investigate the integration of this technology with other functionalities for advanced applications.

The current design exhibits a slower tuning speed compared to electrically controlled metasurfaces. The slight discrepancies observed between simulated and measured results can be attributed to fabrication tolerances. Future work could investigate more robust fabrication methods to minimize these discrepancies.