Nested Split-Ring Dual-Resonant Double-Negative Metamaterial Unit Cell for 5G mmWave and D-Band Sub-THz Applications

This article presents a nested split-ring resonator (SRR) metamaterial unit cell which demonstrates dual-resonant double-negative (DNG) behavior for the 5G mmWave and D-band sub-THz region. The proposed geometry contains a scaled inner SRR pair within an outer SRR pair that enables operation at two different resonant frequencies while maintaining a single-layer planar platform. Full wave simulations are performed through a two-port wave excitation set up with proper PEC/PMC symmetry boundaries (normal incidence) to obtain the scattering parameters. The lower resonance is tuned around 28.9 GHz to cover the 5G FR2 (Frequency Range 2) mmWave region and the upper resonance is tuned around 113.3 GHz, in accordance with the allocated D-band window (111.8–114.25 GHz) which is relevant for the emerging 6G sub-THz band. Effective-medium parameters are extracted from the simulated S-parameters by the standard Nicolson–Ross–Weir (NRW) retrieval approach. The simultaneous presence of negative effective permittivity and permeability around the resonance region confirms double-negative (DNG) behavior. The proposed passive unit cell is a compact building block for future planar metasurface/microwave devices and can also be incorporated as a passive loading layer or superstrate in an antenna system.