| In the military and civilian fields,wireless communication facility and system working in different frequency band has been widely used,which makes the electromagnetic environment of the facility and system gradually complex.On the one hand,external irradiation electromagnetic waves can permeate into the internal space of wireless communication facility and system by electromagnetic induction or aperture coupling,further acting on the signal transmission cable and electronic interaction,which leads to device,module or system performance degradation or failure easily.On the other hand,under the irradiation of external electromagnetic waves,the space scattering waves from the facility and system further complicate the surrounding electromagnetic environment,and the strong space scattering waves are very likely to cause mutual interference to other facility and system in the neighboring environment again.Thus,enhancing the ability of the target in complex electromagnetic environments of external electromagnetic irradiation protection and scattering characteristics manipulation is an effective technological approach to ensure targets normal running and improve the electromagnetic environment.According to the electromagnetic compatibility theory,an effective technological measure to control electromagnetic interference is to control the propagation path of the electromagnetic interference.What's more,electromagnetic scattering characteristics manipulation can be designed to make the primary scattering of the target redirect at the minor threat angle domain,reducing the electromagnetic interference intensity to other facility or system within the major threat angle domain.Aiming at these two objectives,in this paper,an irradiation protection design based on the passive electromagnetic metasurface in wireless communication environment is firstly studied.Then,by loading varactors,the function of the passive electromagnetic metasurface is further extended.An active electromagnetic metasurface manipulating the electromagnetic scattering characteristics of the target dynamically is designed.In terms of irradiation protection against external electromagnetic waves,based on the transmission metasurface combined with a singer circuit analog absorber,a composite array structure is designed,which can be used to realize electromagnetic shielding and scattering reduction at low frequencies,and provide wireless communication window at a high frequency at the same time.What's more,the composite array structure can achieve the reciprocity transformation between the spherical and plane wavefront,which is helpful to improve the quality of communication.Firstly,based on the transmission phase compensation principle,a transmissive metasurface lens with wide-band focusing characteristic is designed to realize transformation between plane and spherical wavefront.By properly constructing the unit cell of the transmissive metasurface lens,wideband focusing effect at the specified focal point is obtained.Furthermore,the reflection behaviour of the lens at frequencies lower than the focusing band is exploited for the sake of a wide band of absorption through incorporating a single lossy layer implemented with resistor-loaded square-loop arrays.A wideband Vivaldi tapered-slot antenna is simply employed as a primary radiation source and placed at the focal point of the layered structure to evaluate the transmissive radiation augmentation effect to antennas.At the design frequency of 11 GHz,it is observed that the effective wavefront transformation of the composite array structure make the main lobe gain of the primary feeding antenna increased by 7.91 d B,and the relative bandwidth of main lobe gain enhancement is36.04%.In the normal incident experiment,it is found that the absorption effect of the composite array structure is more than or equal to 10 d B in the relative bandwidth range of108.43% compared with the metasurface lens.In addition,the scattering reduction of the composite array structure and the stability of the electromagnetic shielding in wide angle domain are analyzed.The composite array exhibits potential of application in shielding enhancement of communication facility or system operating in sensitive electromagnetic environment due to the characteristics of radiation gain enhancement,scattering reduction,and electromagnetic shielding effect.In order to improve the electromagnetic working environment by adjusting the electromagnetic scattering characteristics of the target,taking into account the dynamic change of the target and its working environment,the dynamic manipulation of the electromagnetic scattering characteristics of the target by active electromagnetic metasurface is studied in this paper.Firstly,an active metasurface physical unit cell structure with a varactor loaded and embedded bias loop is designed,and the equivalent circuit model of the active metasurface is extracted and analyzed to describe the manipulation mechanism of active metasurface reflection characteristics by varactors loaded.Then,the active metasurface designs about the plane and cylindrical surface conformal are obtained by properly forming the unit cell structures into arrays on the plane and cylindrical surface respectively.A programmable DC voltage output amplifier is used to switch the active metasurface between different operating states quickly,so that the multi-channel independent and controllable DC bias voltages are realized.The active metasurface can present an electrically adjustable reflection phase gradient for different incident angles and predetermined reflection angles by adjusting the bias state of varactors in different units of the active metasurface in real time.Then the scattering energy is directed to the predetermined reflection angle by the generalized reflection law.Based on the law of conservation of energy,the scattering intensity in other angular domains can be reduced,and the electromagnetic environment can be improved in a wide angular domain.The redirected primary scattering energy of the plane and cylindrical surface structures are characterized by the radar cross-sections of different monostatic and bistatic scenarios.Through the design of the reconfigurable scattering pattern,the dynamic manipulation of the scattering characteristics and the improvement of the electromagnetic environment in a wide angle domain are demonstrated.The dynamic manipulation effect of the electromagnetic scattering characteristics is verified by monostatic and bistatic experiments. |
PDF Full Text Request