PT-Symmetry and Non-Hermitian Wave Transport in Microwaves and RF Circuits

Many novel concepts in \(\mathcal {PT}\)-symmetric wave transport were initially explored and demonstrated in the conceptually simpler and experimentally more accessible framework of active electronic circuits. These include eigenmode analysis and spatio-temporal dynamics of the stored energy in static and in periodically driven (Floquet) \(\mathcal {PT}\)-symmetric circuits, and \(\mathcal {PT}\)-symmetric scattering in both the linear and nonlinear regime. We review several of these advances – often stretching the borders of investigation to the most general area of non-Hermitian wave transport where concepts like coherent perfect absorbers, gain-induced lasing shut-down, and asymmetric transport are naturally emerging.