Coupled Resonator-Based Metasurface Reflector With Enhanced Magnitude and Phase Coverage

A metasurface reflector unit cell is proposed for achieving a near-complete range of complex reflectance (i.e., magnitude and phase) for versatile beamforming capabilities. The unit cell is based on tunable 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 that results in an enhanced complex reflectance range at the desired frequency. To provide 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 frequency, damping coefficient, 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, sidelobe 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.