Dynamic Metasurface Reflectors Based on Coupled Resonators for
Simultaneous Magnitude and Phase Control
Abstract
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.