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Beijing, China

Li W.-Q.,Xian University of Technology | Li W.-Q.,Xian University of Science and Technology | Mu K.,China Spacesat Co. | Xia R.-H.,Xian University of Technology

We clarify the transient and equilibrium charging characteristics of grounded dielectrics due to low-energy defocused electron beam irradiation by a three-dimensional self-consistent simulation model. The model incorporates the electron scattering, transport and trapping. Results show that some electrons can arrive at the grounded substrate due to the internal field and density gradient, forming the leakage current. The transient charging process tends to equilibrium as the surface potential decreases and the leakage electron current increases. The positive and negative space charges are distributed alternately along the beam incident direction. In the equilibrium state, the surface potential and leakage electron current decrease to stable values with increasing film thickness and the trap density, but with decreasing electron mobility. Moreover, the surface potential of the dielectric thin film exhibits a maximum negative value with variation of the beam energy; for example, under the condition of the film thicknesses 0.5μm and 2μm, the maximum negative values of surface potentials are -13. V and -98. V in beam energies 2. keV and 3.5. keV, respectively. However, for the thick film, the surface potential decreases with the increase in beam energy. © 2010 Elsevier Ltd. Source

Bai J.,National University of Defense Technology | Shi D.,China Spacesat Co. | Fu Y.,National University of Defense Technology
Guofang Keji Daxue Xuebao/Journal of National University of Defense Technology

Mushroom electromagnetic bandgap structure shows surface-wave bandgap and in-phase reflection, these two characteristics were simultaneously used for designing the waveguide slot array antenna. The surface-wave bandgap was used to suppress the surface-wave in antennas and arrays, which results in radiation performance improvement. In addition, the in-phase reflection could be used to reduce the RCS level of antennas and arrays, so as to improve their total performances. A sample of four-element EBG waveguide slot array antenna was made, and the indexes of mutual coupling, radiation pattern and RCS of the sample were tested. The result is similar with the theoretical expectation, which has effectively reduced the mutual coupling and the RCS level of antennas and arrays. ©, 2015, National University of Defense Technology. All right reserved. Source

Huang Q.-D.,China Spacesat Co. | Yang F.,China Spacesat Co. | Zhao J.,China Spacesat Co.
Yuhang Xuebao/Journal of Astronautics

Drift angle exists in dynamic imaging for an agile satellite in three axis attitude maneuvering, e. g. the direction of image acquisition is not parallel with the satellite platform motion. Based on TDICCD imaging principle, drift angle in dynamic imaging procedure is analyzed. The analytical mathematic expression of drift angle in dynamic imaging is derived from velocity vector method. Numerical simulation results show that when the angle between the camera snap speed and ground speed is 0° or 180°, the drift angle generated by the rotation of the earth is small in value; when the angle is 0°<η<180°, the drift angle produced by the earth's rotation and orbital motion is large in value. Besides, with high maneuverable satellites, when the camera snap speed is perpendicular to the natural platform motion, the drift angle increases with the increasing geographical latitude. The yaw controlling method is effective to minimize the drift angle in the dynamic imaging technology. Source

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