Study Of Three-dimensional Absorptive Frequency-selective Reflection And Transmission Structures

With the rapid development of radar detection technology,unobservable(stealth)platforms play an important role in modern military systems.In many techniques that can reduce the radar cross section(RCS)of an antenna,the frequency-selective surface/structure as a stealth radome is now widely used,and related research continues.In this paper,the proposed structure is absorbing,that is,electromagnetic waves outside the pass-band(or reflection band)are absorbed rather than reflected,which is more conducive to the realization of "stealth" performance.This paper mainly introduces the three-dimensional absorptive frequency-selective reflection and transmission structure.The research content of this paper mainly has the following parts:1.A reflection band is designed to move the three-dimensional absorptive frequency-selective reflection(AFSR)structure,which has a reflection band with an absorption band on each side of the reflection band.The 3D AFSR utilizes the intrinsic reflection band and higher order absorption band of a wideband 3D absorber.By simply loading a printed gap capacitor in the structure,the adjustment of the reflection band can be achieved by changing the metal width of the capacitor structure and the depth of the gap to change the value of the capacitance.A design example is presented,with a reflection band of 24.7% fractional band width(FBW),a lower absorption band of 72.5% FBW,and a higher absorption band of 48.6% FBW.2.A band-pass frequency selective structure in which the pass-band of the parallel plate waveguide structure can be adjusted is designed.By analyzing the relevant principles,the range of the pass-band is broadened,and the medium is filled between the parallel plates,and the dielectric substrate with different relative dielectric constants is changed,or the holes are punched on the dielectric substrate,thereby obtaining different equivalent relative dielectrics.That enables the adjustment of the pass-band.3.A three-dimensional absorptive frequency-selective transmission(AFST)structure was designed.Its general operating principle is demonstrated,such that the 3D AFST can be seen as a combination of a 3D AFSR and a 3D band-pass frequency selective structure,which can independently contribute to the absorption and transmission,respectively.A set of guidelines is proposed to facilitate the design.A prototype of the proposed AFST is fabricated and measured.The measured results show that the transmission band is with a minimum insertion loss of 0.43 d B.And the transmission band of 30% FBW.Moreover,the lower and higher absorption bands are with 63.9 % and 47.6 % FBW,respectively.The proposed AFST has a simpler structure,wider lower absorption bandwidth,and thinner thickness compared with previous structures.