Study Of Nonreciprocal Transmission Line Based On Electromagnetic Surface Waves

With the development of integrated systems,there are more requirements on the reciprocal devices,such as miniaturization,integration,low insertion loss and etc.Recently,the one-way electromagnetic wave transmission property of gyromagnetic medium surface under external bias magnetic field has been found,which provides a new way to study unidirectional propagation of the electromagnetic wave.The anisotropic permeability tensors of gyromagnetic medium have been deduced under external bias magnetic field.The conditions,that cause the broken of gyromagnetic medium's Time Reversal Symmetry,have been analyzed,which will excite the chiral edge states(CESs)with one-way transmission property on the gyromagnetic magnetic photonic crystal's edge.As an application,a one-way photonic crystal waveguide structure has been designed by means of the gyromagnetic photonic crystals.The simulation results show that the structure has obvious one-way transmission property in 11.7GHz-12.3GHz.To avoid large dimension,high loss of the periodic photonic crystal structure,the magnetic surface states(MSPs)of gyromagnetic medium has been analyzed.By introducing the gyromagnetic medium tensor permeability into Maxwell equation under external bias magnetic field,the bulk and surface dispersion curves of gyromagnetic medium have been given,which prove that the gyromagnetic medium's edge supports the one-way propagation of electromagnetic waves in a particular frequency range.On the basis of the above research,by setting the gyromagnetic medium as the boundary of slab waveguide,a one-way slab waveguide was designed,which realize the one-way transmission property in 7.5GHz-9GHz.Meanwhile,to deal with the integration of slab waveguide,a new kind of one-way substrate integrated waveguide(SIW)structure has been proposed.The simulation and experimental results indicate that the structure are obvious of one-way transmission property in 6.9GHz-7.5GHz.In order to further reduce the insertion loss,based on MSPs and couple-mode theory,a new design method of compact low-loss one-way transmission structure is presented.As an example,a one-way transmission structure composed of microstrip line and one-way ferrite loop has been realized.Simulation and experimental results indicate that the structure has excellent forward transmission efficiency and good backward isolation in 10.1 GHz-11.2GHz.Further,the bandwidth characteristics of the one-way microstrip transmission structure has been studied.A broadband one-way transmission structure is obtained by structures cascading.Simulation results show the cascading structure possesses good one-way transmission characteristics in 9.8GHz-12.2GHz.Finally,based on MSPs,low-frequency ultra-thin absorbing structure has been proposed.By breaking its time reverses symmetry,the gyromagnetic medium completely converts the incident electromagnetic wave into surface wave and restricts the surface wave propagating unidirectionally along the surface,which make the structure be good electromagnetic absorber.An absorber with thickness of 2.5mm has been designed as an example.Simulation results show that the structure has excellent absorbing properties in 0.59GHz-0.64GHz.In order to further expand the absorbing bandwidth,a broadband low-frequency ultra-thin absorbing structure has been realized by cascading above structures with different parameters.The simulation results show that the cascaded structure has excellent absorbing properties in 0.51GHz-0.64GHz.