Research On Multi-functional Frequency Selective Surface And Antenna

With the increasing complexity of the space electromagnetic environment and the diverse needs of practical engineering applications,the research on multi-functional frequency se-lective surfaces(FSS)and the combination of frequency selective surfaces and antennas to improve antenna's performance has very important practical significance.On the one hand,the active frequency selective surface(AFSS)changes the operating frequency or transmis-sion characteristics of the FSS by loading external excitations,so as to achieve flexible con-trol of electromagnetic waves,which can be applied to the reconfigurable design of antennas.On the other hand,the frequency selective rasorber(FSR)has received widespread attention because it can receive or transmit signals at a specific frequency and absorb incoming waves in any direction at a certain frequency band to realize the omni-directional stealth of the an-tenna.This thesis mainly focuses on the active frequency selective surface(AFSS)and the miniaturized/flexible frequency selective rasorber(FSR),and applies the designed structure to the antenna pattern reconfigurable or stealth technology.The main research contents of this thesis are as follows:1.The equivalent circuit models of the frequency selective surface,the absorber and the fre-quency selective rasorber are introduced.Three types of S-parameter curves are synthesized with the equivalent circuit of the frequency selective rasorber,the absorption band below the transmission band,the transmission band in the absorption band,and the absorption band above the transmission band.This provides a theoretical basis for subsequent design.2.A graphene-based terahertz dual-frequency independently adjustable active frequency selective surface is designed.The FSS uses the tunable characteristics of graphene chemi-cal potential,and can independently switch between high transmission and large reflection states in the two frequency bands of 0.96THz and 1.21THz.Subsequently,by combining the active frequency selective surface radome and the omnidirectional monopole antenna located in the center of the radome,a dual-frequency independently controllable pattern re-configurable antenna is designed.By adjusting the different combinations of AFSS states on each face of the radome,flexible beam control such as dual-frequency 360-degree beam scanning/omnidirectional radiation/multi-directional radiation can be realized.3.A miniaturized frequency selective rasorber with the absorption band below the trans-mission band is designed.By introducing 2.5D metallized vias on the impedance surface to interweave and connect the metal of the upper and lower layers,the equivalent induc-tance and equivalent capacitance of the impedance surface is increased,thereby reducing its resonance frequency,and achieving the purpose of miniaturization.This structure realizes broadband absorption between 1.96GHz-10.2GHz,and the fractional bandwidth is as high as 135.5%.It realizes wave transmission at 12.83GHz,and the insertion loss is only 0.23d B.The cell period is about 0.039?_L,and the cell thickness is about 0.067?_L,so the degree of miniaturization is excellent.The screen printing process of graphene resistive film replaces the welding process of the lumped resistor,which simplifies the manufacturing process.The measured results are in good agreement with the simulation results.4.A flexible frequency selective rasorber with the transmission band in the absorption band is proposed.The graphene resistive film is used as an omnidirectional planar resistor to replace the lumped resistor,and the flexible PDMS substrates replaces the air substrates to play a supporting role to achieve good mechanical stability of the structure.The transmission poles between the two stop bands are used to achieve the transmitting effect,and a transmis-sion zero is introduced on the left and right sides of the passband respectively to improve the out-of-band selection characteristics.Conformal simulation verification was performed on the designed FSR.It still has a stable S-parameter response under the condition of a large angle of 128.3 degrees.The measured results are in good agreement with the simulation results.Finally,using the FSR as a radome combined with a microstrip antenna to verify the performance of its RCS reduction.The simulation results show that it can achieve a 7d B RCS reduction outside the band without affecting the antenna's radiation performance.