Experimental Characterization of a Waveguide-Fed Varactor-Tuned Metamaterial Element Using the Coupled Dipole Framework

We confirm experimentally that the essential electromagnetic properties of a single, waveguide-fed, tunable metamaterial radiator can be described within a coupled dipole framework, providing a foundation for metasurface array antenna design. The metamaterial element considered here is an electrically small aperture consisting of a complementary electric-LC resonator with its resonance frequency controlled by a pair of varactor diodes. Using the dipole framework, we reduce the detailed properties of the tunable element—which is a complex composite of electrically small resonant opening and bias circuitry—to a combination of effective magnetic and electric polarizabilities, with the magnetic response modeled by a Lorentzian resonance with a dc component. Experiments reveal that the designed element scatters the excitation fields into the waveguide and free space predominantly as a polarizable magnetic dipole, with a polarizability matching that is predicted from a simulation-based polarizability retrieval. This experimental analysis validates the dipole framework, unlocking the potential for improved holographic beamforming approaches for the design and analysis of reconfigurable metasurface antennas.