Negative capacitors and inductors enabling wideband waveguide metatronics

Waveguide metatronics, known as an advanced platform of metamaterial-inspired circuits, provides a promising paradigm for millimeter-wave and terahertz integrated circuits in future fifth/sixth generation (5/6G) communication systems. By exploiting the structural dispersion properties of waveguides, a lumped type of waveguide integrated elements and circuits could be developed in deep subwavelength scales with intrinsic low loss and low crosstalk. In this study, we focus on constructing negative capacitors and inductors for waveguide metatronics, effectively expanding the operating frequency range of waveguide integrated circuits. The incorporation of negative elements enables wideband impedance matching in waveguide, which have been both theoretically explored and experimentally validated within the waveguide metatronics paradigm. Furthermore, we have demonstrated that the negative elements can also be realized in the optical domain through the utilization of a silicon waveguide with photonic crystal cladding, indicating the feasibility and universality of wideband waveguide metatronics. The negative lumped elements could boost the progress of the waveguide metatronic technique, achieving superior performance on the conventional lumped circuits within waveguides that solely rely on positive elements.