Active Frequency Selective Surface Technique And Application

Frequency selective surfaces(FSS)are widely used in satellite communication systems,meta-material fabrication,electromagnetic waves shielding and antenna radar cross section(RCS)reduction,where RCS reduction attracts more attention since its special purpose in military.The stealth radome based on FSS can be seen as a good explanation,which is an essential part in the stealth aircraft as well as the stealth battleship.However,with the development of antennas to multi-frequency and broadband,it is difficult to design FSSs suitable for such antennas.To solve this problem,the concept of Active Frequency Selective Surface(AFSS)was proposed.AFSS is realized by introducing a specific excitation source in the FSS.Its resonant frequency or filtered characteristic can be changed by changing the source,thereby satisfying the application requirements of different environments.Although AFSS can meet the application requirements of different environments,there are still some deficiencies in the bistatic RCS reduction,which is determined by the FSS's mechanism of RCS reduction.As an extension,the design method of Frequency Selective Absorb Surface(FSAS)is studied in this dissertation to realize bistatic RCS reduction.In addition,the AFSS is applied to the mentioned FSAS to achieve the design of active FSAS.The key to designing a AFSS is how to introduce the necessary incentives into the FSS structure and effectively control its changes.In addition,the influence of these incentives on FSS filtering characteristic must also be considered.This dissertation takes the above key issues as the research intents and focuses on the following aspects:1.The design method of AFSS based on coupling mechanism is investigated.The concept of coupling FSS has been mentioned in many dissertations.The key is how to effectively control the coupling excitation.Traditional methods such as rotation and movement are with great difficulty in actual manipulation.To solve this problem,the method of changing the longitudinal displacement between FSS elements is introduced.In addition,the performance of flatness in the passband is effectively improved by cascading the AFSS unit cells up and down.At the same time,this cascading AFSS shows a stable performance with respect to the incident angles and polarizations of EM waves.2.The design method of a miniaturized AFSS based on varactor diodes is investigated.As is well known,varactor diodes are widely used in tuning circuits since their equivalent capacitance can vary with the bias voltage across the components.Since the FSS can be analyzed by the means of equivalent circuit model,the resonant frequency can also be effectively changed when varactors are loaded in the units.However,a bias network needs to be arranged carefully in the unit cells to effectively change the state of varactors.Thus,this dissertation describes in detail the design principles and methods of the bias network.A miniaturized AFSS structure with good angular stability and polarization independence is introduced based on the proposed method.Although AFSS has many advantages over FSS,it still has some defects in bistatic RCS reduction.To solve this problem,the design method of FSAS is discussed.The contents are as follows:1.Design method of FSAS based on parallel LC resonators is investigated.Firstly,the concepts and advantages of FSAS are described.Then the principle of type of loading parallel LC resonant circuit is introduced and a “absorbing-transmitting-absorbing” FSAS is designed by using this method.Meanwhile,the performance of FSAS in bistatic RCS reduction over FSS is verified by using the full-wave simulator HFSS.Next,a AFSS based on PIN diodes is designed and applied to FSAS.By changing the state of AFSS,the FSAS performance can change from “absorbing-transmitting-absorbing” to “absorbing-reflecting-absorbing”.2.The method of designing a miniaturized FSAS is investigated.Miniaturization is an important feature,especially in a compact environment.Therefore,the method of designing a miniaturized FSAS is proposed.It is realized by designing the miniaturized absorptive surface and the miniaturized transmission surface.Simulations show that the proposed miniaturized FSAS can realize a good bistatic RCS reduction while maintaining a good performance of “absorbing-transmitting-absorbing”.