Yuntao He

High-Frequency Method for Terahertz Radar Cross Section of Conductive Targets in Free Space

The high-frequency method for the prediction of the terahertz (THz) radar cross section (RCS) of conductive targets with extremely electrically large size in free space was presented. In order to consider the scattering flelds of the perfectly electric conducting (PEC) targets with extremely electrically large size in free space, the Greens function was introduced into the conventional physical optics (PO) method which was combined with the graphical electromagnetic computing (GRECO) method and improved using the partition display algorithm. The shadow regions were eliminated quickly by displaying lists of OpenGL to rebuild the targets, and the geometry information was attained by reading the color and depth of each pixel. The THz RCS of conductive targets can be exactly calculated in free space. The RCS comparison between the partition display GRECO prediction by the self-written Visual C++ 2010 program and the simulation of FEKO software with the large element PO method proves the validity and accuracy of the proposed method. The results provide an important basis and method for the potential applications of THz radar in many flelds such as military, astronomy and remote sensing.

Reflection of Laguerre-Gaussian beams carrying orbital angular momentum: a full Taylor expanded solution.

Partial reflection of linearly polarized Laguerre-Gaussian beams incident at a dielectric interface are studied beyond the paraxial regime. Based on the angular spectrum method and Taylor series expansion, we derive exact analytical expressions for the reflected electric field. This result holds in both the paraxial and nonparaxial regimes. The result is then extended to beams of arbitrary polarization and used to analytically calculate the transverse and longitudinal shifts of the beams center of gravity. Finally, several numerical examples are performed to verify the analytical formulas we derived near the Brewster angle.

High-Frequency Method for Scattering from Coated Targets with Extremely Electrically Large Size in Terahertz Band

Abstract This article presents a high-frequency method for the prediction of radar cross-section of coated targets with extremely electrically large size in the terahertz band in free space. To consider the scattering characteristics of the coated targets with a rough surface in the terahertz band, taking into account the effect of surface roughness, the reflection coefficients on the smooth coating surface can be modified; the equivalent electric and magnetic currents on the surface can then be corrected by the modified reflection coefficients to obtain the electric and magnetic induced current densities on the rough coating surface. Therefore the physical optics method, which was combined with the graphical electromagnetic computing method and improved using the partition display algorithm, can be used to solve the scattered fields, and the radar cross-section of the coated targets with a rough surface in the terahertz band can then be obtained. Numerical results for several coated targets, such as the mother warhead of the Minuteman III intercontinental ballistic missile and VFY-218 aircraft, are given and discussed. The results provide an important basis and method for applications of terahertz radar in many fields, such as military, astronomy, and remote sensing, in the future.

Optical aperture synthesis imaging with fractional Fourier-domain filtering

The fractional Fourier transform, which is a generalization of the classical Fourier transform, is introduced into an optical aperture synthesis (OAS) system by which imaging of an astronomical object can be achieved. We introduce fractional Fourier optical imaging and fractional Fourier-domain filtering (FFDF), and then present the schematic diagram of an OAS imaging system with FFDF. The modulation transfer function of an OAS system with FFDF is compared with that of an OAS system in the same condition. The result indicates that the OAS system with FFDF has larger practical cutoff frequency when the fill factor is smaller. Furthermore, the quality of imaging and restoration also demonstrates this conclusion.

Application of millimeter-wave photonics technology in passive millimeter-wave imaging

Passive millimeter-wave imaging is attractive due to the ability to obtain images in low-visibility conditions. In this paper, a passive millimeter-wave imaging method using photonic processing is presented. The principle of the millimeter-wave photonic signal processing method is described. The relationship between the signal conversion gain and the component parameters is discussed. The noise characteristic of this detection method is analyzed. A millimeterwave radiometer using photonic processing is presented in this paper. A passive millimeter-wave scanning imaging system using this processing method was implemented. The imaging experiment results show that this imaging method is effective.