A novel metasurface reflector unit cell based on two coupled resonators is proposed and demonstrated for real-time reconfigurable beamforming in the X-band (8-12 GHz). The unit cell is composed of a split-ring resonator (SRR) with tunable capacitance and a dipole-ring resonator (DRR) with tunable resistance, whose collective variations allow for control over the complex reflectance at a desired frequency. To gain physical insight into its working mechanism, the proposed unit cell is modeled as a coupled Lorentz oscillator using the surface susceptibility description of the unit cell. Thereafter, a metasurface reflector based on the proposed unit cell is demonstrated in full-wave simulations to achieve various beamforming examples, such as beam-steering, side-lobe level control, beam-steering with amplitude control, and multi-beam patterns, from a single normally incident plane wave excitation. Three metasurface reflectors are fabricated to experimentally demonstrate the proposed concept; the first is based on a SRR with a varactor diode, the second is based on a DRR with a PIN diode, and the third is based on the proposed coupled SRR-DRR configuration with both varactor and PIN diodes, for simultaneous magnitude and phase control. The metasurface reflector based on the coupled resonator unit cell is experimentally demonstrated to achieve versatile beam transformations including beam-steering with amplitude control and multi-beam patterns.

A novel shape-shifting mechatronic reflector system is proposed and demonstrated experimentally with a variety of real-time beam-forming examples. The reflector system consists of a 1D array of panels of sub-wavelength split ring resonators (SRR) loaded with PIN-diodes for reflection magnitude control, and a stepper motor array which de-embeds each panel to accomplish column-by-column phase control, thus offering excellent decoupling between the magnitudes and phases. A complete system prototype is built including a printed circuit board (PCB) based resonator array forming the reflector front end, a stepper motor array assembly, a custom built chassis using 3D printed parts and a fully programmable analog and digital electronic backend for PIN-diode biasing and motor control. The real-time beam-forming feature of the proposed reflector system is further experimentally demonstrated using the illustrative examples of single beam steering with gain control and generation of asymmetric dual beam radiation patterns where the two beams are independently controlled - a capability unlocked through achieving true decoupling between the reflection magnitudes and phases.

A metasurface reflector unit cell is proposed for achieving near-complete-range of complex reflectance (i.e., magnitude and phase) for versatile beamforming capabilities. The unit cell is based on coplanar coupled resonators: a split ring resonator (SRR) with a lumped capacitor and a lumped resistor, and a dipole ring resonator (DRR) with another lumped capacitor. The DRR inserted inside the SRR creates a coupled resonance configuration which results in an enhanced complex reflectance range at the desired frequency. To provide a physical insight and explain the operation principle of the structure, the response of the unit cell is modeled as a coupled Lorentz oscillator via the effective surface susceptibilities, where a unique plasma, damping constant, and resonant frequency can be attributed to each resonator. The proposed unit cell is demonstrated in an array configuration for linear-polarized beamforming, where full-wave simulations are used to demonstrate beam-steering, gain control, side-lobe level control and dual- and triple-beam generation, as illustrative examples. Finally experimental demonstration is performed to validate the full-wave results and obtain in-depth electrical characterization of the reflectors.

A simple method is proposed to characterize metasurface unit cells using rectangular waveguide. The method maps the S-parameters obtained using a dominant-mode waveguide to the S-parameters of fundamental Floquet mode for a plane wave incident at any desired angle. The mapping between the dominant waveguide mode and the fundamental Floquet mode is executed by extracting the equivalent surface susceptibilities of the metasurface unit cell. The results obtained from the proposed method show good agreement with the full-wave simulation results of the metasurface unit cell.

A 1-bit reconfigurable metasurface reflector is designed. It can provide beam-steering of circularly polarized (CP) re- flected waves when a linearly polarized (LP) plane wave is incident upon it. The unit cell of the metasurface provides 1-bit coding (‘bit-0’ and ‘bit-1’) for both v- and u-polarized reflected waves when two distinct reverse bias voltages (3 V and 20 V) are applied to the varactor diodes. Using such unit elements, a 20×20 array is constructed. During the array construction, a quadrature phase difference is main- tained between the v- and u- polarized components of each element. Using both theory and full-wave simulation re- sults, it is shown that the proposed metasurface reflectarray can steer two symmetrically deflected CP beams with two opposite handedness for a LP plane wave incidence.