We report the generation of helical electromagnetic radiation in a microwave cavity resonator, achieved by introducing mirror asymmetry, i.e., chirality, through a controlled geometric twist of the conducting boundary conditions. The emergence of this electromagnetic helicity is attributed to a nonzero spatial overlap between the electric and magnetic mode eigenvectors, quantified by $\text{Im}[{\vec{\mathbf{E}}}_i\left(\vec{r}\right)·{\vec{\mathbf{H}}}_i^{*}\left(\vec{r}\right)]$, a feature not observed in conventional cavity resonators. This phenomenon originates from magnetoelectric coupling between nearly degenerate TE and TM modes, resulting in a measurable frequency shift of the resonant modes as a function of the twist angle, $\varphi$. By dynamically varying $\varphi$, we demonstrate real-time, macroscopic manipulation of both electromagnetic helicity and resonant frequency. In addition to the bulk helicity induced by global geometric twist, internal helical corrugations break structural symmetry on the surface, introducing an effective surface chirality ${\kappa }_{\text{eff}}$, which perturbs the resonant conditions and contributes to asymmetric frequency tuning. Furthermore, we investigate the underlying mode coupling dynamics of the system, highlighting strong photon-photon interactions.

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• Chirality
• Magnetoelectric effect
• Nonlinear optics
• Optical & microwave phenomena
• Optomechanics
• Photonics
• Microwave techniques