| As an important device for receiving and transmitting electromagnetic signals,antennas are an essential part of various types of wireless equipment.However,as a special scatterer,antennas are a significant scattering source for various military equipment platforms.In order to improve combat capability and survivability,the scattering suppression of the platforms is required to achieve low detectability,and the scattering suppression of antennas is particularly important.In addition,various types of wireless equipment put forward higher requirements on the properties of antennas,such as bandwidth,polarization,gain,and efficiency,which makes the development of antennas along the trend of high performance,multi-function,and integration.Electromagnetic metamaterials are new artificial materials with rich electromagnetic properties,and electromagnetic metasurfaces developed from electromagnetic metamaterials have wide applications in antenna scattering suppression and radiation control.By loading the electromagnetic metasurfaces,the antenna scattering can be suppressed while maintaining the radiation performance.Besides,the transmission/reflection-type metasurfaces can effectively regulate the propagation direction,amplitude,phase,polarization,and other properties of electromagnetic waves,providing new design schemes for regulating the radiation performance of antennas.Based on the new theory and new technology of electromagnetic metamaterials,this dissertation carries out the research work of antenna scattering suppression and radiation control technology,which is closely related to the latest development demands of electromagnetic metasurfaces.The main research contents of this dissertation are summarized as follows.1.Based on the demand of antenna broadband scattering suppression,the research of broadband and miniaturization technology for frequency selective surface(FSS)is carried out,and a dual-band dual-polarized bandpass FSS radome with a large band ratio and broadband out-of-band suppression properties is designed.Firstly,a dual-polarized squaregrid FSS is first designed based on a spoof surface plasmon polariton(SSPP)structure,which is capable of forming a broadband bandstop response and a passband in the lower frequency band.Next,a dual-polarized interlaced-grid FSS is formed by combining two interlaced square-grid FSSs.The response formed by the short branches of the interlacedgrid FSS is enhanced due to the closer arrangement of the adjacent vertical layers,resulting in a passband in the higher frequency band and a bandstop response with wider bandwidth between the lower and higher passbands.The center frequencies of the two passbands of this interlaced-grid FSS are 2.5 GHz and 15.5 GHz,respectively,corresponding to a band ratio of 6.2.The broadband bandstop response between the two passbands has a -10 dB stopband bandwidth of 116.6%.2.For the scattering suppression demand of large aperture antennas,the design technology of bandstop reflection phase-shifting metasurface is researched,and a mesh-type low radar cross section(RCS)reflectarray antenna is proposed,which consists of a feed and a meshtype reflector.The mesh-type reflector is composed of phase-adjustable bandstop reflection elements.Due to the hollowed-out design,the mesh-type reflector is optically transparent.Since the reflection branches of the bandstop reflection element can excite the SSPP modes,it has a high reflection amplitude in the stopband and a high transmission amplitude in the passband.In the stopband,the mesh-type reflector can reflect the quasi-spherical waves radiated by the feed and realize beam convergence,while outside the stopband,the incident electromagnetic waves pass through the reflector,so the reflector has low RCS properties in the out-of-band.The proposed mesh-type reflectarray antenna has a 1-dB gain bandwidth of 13.9%(9.4-10.8 GHz).Compared with the reference antenna,this reflectarray antenna has low RCS properties in the frequency range of 1.0-8.5 GHz and 12.0-19.0 GHz.3.To address the demand for bidirectional circularly polarized beam coverage,the design technique of circularly polarized transmission-reflection metasurface is investigated,and a shared-aperture dual-band circularly polarized transmit-reflect-array(TRA)antenna is proposed,which consists of an oblique 45° linearly polarized feed and a shared-aperture TRA.The shared-aperture TRA consisting of three-dimensional(3-D)cross-shaped TRA elements is a mesh-type structure with optical transparent properties.Since the 3-D crossshaped TRA element is independent of polarization and can adjust the phase of reflected waves and transmitted waves in different frequency bands,the shared-aperture TRA can convert the oblique 45° linearly polarized waves radiated by the feed into circularly polarized reflected waves and circularly polarized transmitted waves at lower and higher frequency bands,respectively.The proposed TRA antenna can form a high-gain circularly polarized reflected beam in the reflection band centered at 6.2 GHz,which has a 3-dB axial ratio bandwidth of 11.2%(5.9-6.6 GHz).Besides,the proposed TRA antenna can form a highgain circularly polarized transmitted beam in the transmission band centered at 8.0 GHz,which has a 3-dB axial ratio bandwidth of 16.0%(7.5-8.8 GHz).4.To achieve the demand of multi-band bidirectional beam coverage,the design technique of multi-band transmission-reflection metasurface is investigated,and a shared-aperture multi-band TRA antenna is proposed,which consists of a broadband feed and a sharedaperture TRA.The shared-aperture TRA is a combination of a broadband transmitarray and a dual-band reflectarray operating at different polarizations.When the feed radiates ypolarized waves,the TRA can form a high-gain transmission beam in a wide frequency band(the center frequency is 8.5 GHz),while when the feed radiates x-polarized waves,the TRA can form a high-gain reflected beam in both the lower frequency band(the center frequency is 7.0 GHz)and the higher frequency band(the center frequency is 10.0 GHz).In order to realize the demand for multi-band and co-polarization bidirectional beam coverage,a broadband transmitarray with polarization conversion properties is designed,which can convert the y-polarized waves into x-polarized waves,so that the polarization of transmitted and reflected beams radiated by the TRA antenna is the same. |
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