Research On High-selectivity Reconfigurable Frequency Selective Surfaces

Frequency selective surfaces(FSS),as a spatial filter,are widely used in the field of space electromagnatic wave regulation such as electromagnetic stealth technology,etc.With the continuous development of the field of electromagnetic field,as the filtering performance of passive FSS cannot be changed,it cannot meet the demands of increasingly complex electro-magnetic environment.Therefore,the reconfigurable frequency selective surfaces(RFSS)is further derived.This thesis mainly focuses on the research hotspots and applications of FSS in recent years,including reconfigurable characteristics,highselectivity,miniaturization,broadband multi-frequency characteristics,and radome with low-scattering profile.The main research works in this thesis are as follows:Firstly,the basic theory of FSS: the working principle of FSS is explained through the equivalent circult model;The basic forms of the second order bandpass response are discussed,and the parameters that affect the filtering response are studied;The regulation effects of PIN diode on FSS filtering response are studied by taking two basic cell structures as examples;The measurement methodology of FSS in free space is introduced.Secondly,a miniaturized,highly-selectivity RFSS with out-of-band suppression characteristics is designed.By analyzing the filter characteristics of the equivalent circuit model which realizes the swichable response of second order passband and stopband,the method of improving the passband transmission and stopband shielding characteristics of switched RFSS is studied,that is to choose a miniaturized structure with large capacitance and small inductance in the design.Through the research of three optimized design examples,the RFSS based on parallel plate capacitance structure is finally designed.The OFF state has high selectivity characteristics,that is,flat passband,steep sideband and outof-band suppression.The center frequency of the passband is 2.5GHz,and the dimension of RFSS element is only 0.039?×0.039?×0.038?(? is the wavelength of the first transmission pole of the passband),and there is no high order harmonics within 22GHz;In the ON state,the transmission coefficient is less than-20 d B in the range of 0?22GHz,which has a good shielding effect.Therefore,the effectiveness of the proposed method is proved.The DC series-parallel circuits are studied,and the DC feed network is designed,which utilizes unit's own structure.On the one hand,the feed network is simplified,and on the other hand,the effectiveness is ensured.A prototype is fabricated and all the proposed performances are verified by simulations and measurements.Thirdly,a RFSS radome with low-scattering profile for radar cross section(RCS)reduction is designed.Firstly,the RFSS that meets the application requirements is studied,and the RFSS based on the cascaded multilayer structure is designed.The OFF state presents dual passband response,the-1d B passband ranges from 3.24?7.08 GHz and 10.89?14.78 GHz,and the relative bandwidth is 74% and 30.3% respectively.It has high selectivity with flat passband and steep sidebands.The dimension is 0.096?×0.096?×0.093?(? is the wavelength of the first transmission pole of the passband).In the ON state,it has good shielding effects on electromagnetic waves in the L,S,C,and X bands.Furthermore,the designed RFSS was used to model the cone dome radome,and the influence of radome on the radiation and scattering characteristics of the antenna system was studied.The simulation results show that the RFSS radome in the OFF state has some impact on the radiation pattern of the antenna,but it can ensure the basic radiation characteristics of the antenna,and it has good RCS reduction effect in ON state.Therefore,the feasibility of the RFSS radome to reduce the RCS of the antenna system is verified.