A novel approach devoted to achieving ultra-wideband radar cross section reduction（RCSR） of a waveguide slot antenna array（WGSAA） while maintaining its radiation performance is proposed. Three kinds of artificial ...A novel approach devoted to achieving ultra-wideband radar cross section reduction（RCSR） of a waveguide slot antenna array（WGSAA） while maintaining its radiation performance is proposed. Three kinds of artificial magnetic conductors（AMCs） tiles consisting of three types of basic units resonant at different frequencies are designed and arranged in a novel quadruple-triangle-type configuration to create a composite planar metasurface. The proposed metasurface is characterized by low radar feature over an ultra-wideband based on the principle of phase cancellation. Both simulated and measured results demonstrate that after the composite metasurface is used to cover part of the antenna array, an ultrawideband RCSR involving in-band and out-of-band is achieved for co-and cross-polarized incident waves based on energy cancellation, while the radiation performance is well retained. The proposed method is simple, low-cost, and easy-tofabricate, providing a new method for ultra-wideband RCSR of an antenna array. Moreover, the method proposed in this paper can easily be applied to other antenna architectures.展开更多
Aerospace structures can be approximately modeled as a combination of canonical structures such as cylinder,cone and ellipsoid.Thus the RCS estimation of such canonical structures is of prime interest.Furthermore meta...Aerospace structures can be approximately modeled as a combination of canonical structures such as cylinder,cone and ellipsoid.Thus the RCS estimation of such canonical structures is of prime interest.Furthermore metamaterials possess peculiar electromagnetic properties which can be useful in modifying the RCS of structures.This paper is aimed at calculating the RCS of an infinitely long PEC circular cylinder coated with one or two layers of metamaterial.The incident and scattered fields of coated cylinder are expressed in terms of series summation of Bessel and Hankel functions.The unknown coefficients of summation are obtained by applying appropriate boundary conditions.The computations are carried out for both principal polarizations.The computed results are validated against the numerical-based method of moments.Further,the variation of RCS of the metamaterial coated PEC cylinder with material parameters,frequency,aspect angle and polarization is analyzed.展开更多
Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment mon...Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.展开更多
A model complex optical potential rewritten by the conception of bonded atom, which considers the overlapping effect of electron cloud, is employed to calculate the total (elastic + inelastic) cross sections with simp...A model complex optical potential rewritten by the conception of bonded atom, which considers the overlapping effect of electron cloud, is employed to calculate the total (elastic + inelastic) cross sections with simple molecules (N2, O2, NO2, NO, N2O) consisting of N & O atoms over an incident energy range of 100 - 1600 eV by the use of additivity rule at Roothaan-Hartree-Fock level. In the study, the complex optical potential composed of static, exchange, correlation polarization plus absorption contributions firstly uses bonded-atom conception. The qualitative results are compared with experimental data and other calculations wherever available and good agreement is obtained. The total cross sections of electron-molecule scattering above 100 eV can be successfully calculated.展开更多
The total （elastic plus inelastic） cross sections for positron scattering from N2 and CO2 over the incident energy range from 30 to 3000eV are calculated using the additivity rule model at Hartree-Fock level. A comp...The total （elastic plus inelastic） cross sections for positron scattering from N2 and CO2 over the incident energy range from 30 to 3000eV are calculated using the additivity rule model at Hartree-Fock level. A complex optical model potential modified by incorporating the concept of bonded atom, which takes into account the overlapping effect of electron clouds between two atoms in a molecule, is employed to calculate the total cross section of positron-molecule scattering. The calculated total cross sections are in good agreement with those reported by experiments and other theories over a wide energy range.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61671464,61701523,and 61471389)
文摘A novel approach devoted to achieving ultra-wideband radar cross section reduction（RCSR） of a waveguide slot antenna array（WGSAA） while maintaining its radiation performance is proposed. Three kinds of artificial magnetic conductors（AMCs） tiles consisting of three types of basic units resonant at different frequencies are designed and arranged in a novel quadruple-triangle-type configuration to create a composite planar metasurface. The proposed metasurface is characterized by low radar feature over an ultra-wideband based on the principle of phase cancellation. Both simulated and measured results demonstrate that after the composite metasurface is used to cover part of the antenna array, an ultrawideband RCSR involving in-band and out-of-band is achieved for co-and cross-polarized incident waves based on energy cancellation, while the radiation performance is well retained. The proposed method is simple, low-cost, and easy-tofabricate, providing a new method for ultra-wideband RCSR of an antenna array. Moreover, the method proposed in this paper can easily be applied to other antenna architectures.
文摘Aerospace structures can be approximately modeled as a combination of canonical structures such as cylinder,cone and ellipsoid.Thus the RCS estimation of such canonical structures is of prime interest.Furthermore metamaterials possess peculiar electromagnetic properties which can be useful in modifying the RCS of structures.This paper is aimed at calculating the RCS of an infinitely long PEC circular cylinder coated with one or two layers of metamaterial.The incident and scattered fields of coated cylinder are expressed in terms of series summation of Bessel and Hankel functions.The unknown coefficients of summation are obtained by applying appropriate boundary conditions.The computations are carried out for both principal polarizations.The computed results are validated against the numerical-based method of moments.Further,the variation of RCS of the metamaterial coated PEC cylinder with material parameters,frequency,aspect angle and polarization is analyzed.
基金The National Natural Science Foundation of China under contract No.41976169.
文摘Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.
基金This work was supported by the National Natural Science Foundation of China under Grant No.10174019.
文摘A model complex optical potential rewritten by the conception of bonded atom, which considers the overlapping effect of electron cloud, is employed to calculate the total (elastic + inelastic) cross sections with simple molecules (N2, O2, NO2, NO, N2O) consisting of N & O atoms over an incident energy range of 100 - 1600 eV by the use of additivity rule at Roothaan-Hartree-Fock level. In the study, the complex optical potential composed of static, exchange, correlation polarization plus absorption contributions firstly uses bonded-atom conception. The qualitative results are compared with experimental data and other calculations wherever available and good agreement is obtained. The total cross sections of electron-molecule scattering above 100 eV can be successfully calculated.
基金This work was supported by the National Natural Science Foundation of China under Grant No. 10574039.
文摘The total （elastic plus inelastic） cross sections for positron scattering from N2 and CO2 over the incident energy range from 30 to 3000eV are calculated using the additivity rule model at Hartree-Fock level. A complex optical model potential modified by incorporating the concept of bonded atom, which takes into account the overlapping effect of electron clouds between two atoms in a molecule, is employed to calculate the total cross section of positron-molecule scattering. The calculated total cross sections are in good agreement with those reported by experiments and other theories over a wide energy range.
