Design And Simulation Of Active Frequency Selective Surface Switchable Rasorbers

Various antennas mounted on weapon platforms such as aircraft are often important contributors to their radar cross section(RCS).In order to reduce the RCS of the antenna,a bandpass radome with frequency selective surface is used.The radome can transmit electromagnetic waves in the working frequency band,and at the same time reflect radar waves in the out-of-band frequency range to other directions.However,this only works for monostatic radar.For bistatic radar or networked radar systems,a rabsorber based on the frequency selective surface was proposed.The rabsorber absorbs the radar wave in the outof-band frequency range while transmitting the electromagnetic wave in the working frequency band of the antenna.In order to further reduce the RCS of the antenna,a switchable rabsorber was proposed.The switchable rabsorber can provide a wavetransmitting window when the antenna is working,and realize broadband wave-absorbing when the antenna is not working.First of all,the equivalent circuit design method of frequency selective surface based on the transmission line theory was analyzed.The basic first-order bandpass resonant circuit was discussed.Next,the active adjustable characteristics of PIN diodes and their power feeding methods were researched.The PIN diode was added into the basic resonant circuit,and the different transmission characteristics of the single-polarized frequency selective surface unit in TE and TM modes were used to design a dual-polarized narrow-band passthrough/reflection switchable bandpass frequency selective surface without additional feed network.Secondly,the design of the second-order bandpass filter was carried out.It is equivalent to the cascade of two first-order basic resonant circuits using transmission line theory.Two design keys of resonant structure and symmetrical structure were obtained.By changing these two structures respectively,two design methods for realizing dual-polarized broadband transmission/reflection switchable bandpass frequency selective surface were discussed.Finally,based on the equivalent circuit analysis method,the rabsorber was investigated.Combined with the adjustable resistance characteristics of the PIN diode,a lossy layer with switchable wave-transmitting window was extansively designed.Combining the designed lossy layer with the previously designed switchable bandpass frequency selective surface,the switchable rabsorber is designed.The scattering characteristics of the composite structure was quickly calculated in MATLAB by using the transmission line theory.