A reconfigurable, self-phase quadrifilar helical antenna was designed at BDS/GPS frequency band. The impedance, gain and directivity of the antenna were studied by HFSS based on FEM （finite element method） and exper...A reconfigurable, self-phase quadrifilar helical antenna was designed at BDS/GPS frequency band. The impedance, gain and directivity of the antenna were studied by HFSS based on FEM （finite element method） and experiment. Results show the beam width of the main lobe of the pattern can reach over 160° with the help of the load on the top of the antenna. And the power of the side-lobe level is very low. In addition, the quadrifitar helix antenna has excellent right-hand circular polarization performance with a beam width of 180°. Both single-frequency and double-frequency communications can be carried out by the antenna in the ranges between 1.2 and 1.8 GHz, with the bandwidth of each frequency about 60 MHz, the simulating and experimental results are nearly the same.展开更多
This paper investigates L∞--estimates for the general optimal control problems governed by two-dimensional nonlinear elliptic equations with pointwise control constraints using mixed finite element methods. The state...This paper investigates L∞--estimates for the general optimal control problems governed by two-dimensional nonlinear elliptic equations with pointwise control constraints using mixed finite element methods. The state and the co-state are approximated by the lowest order Raviart-Thomas mixed finite element spaces and the control is approximated by piecewise constant functions. The authors derive L∞--estimates for the mixed finite element approximation of nonlinear optimal control problems. Finally, the numerical examples are given.展开更多
基金The research is supported by Shanghai Shuguang Plan Project （No： 15SG44） and NSFC of China （No： 51579143, 51379121 and 61304230） and China Postdoctoral Science Foundation （No： 2015M581585）.
文摘A reconfigurable, self-phase quadrifilar helical antenna was designed at BDS/GPS frequency band. The impedance, gain and directivity of the antenna were studied by HFSS based on FEM （finite element method） and experiment. Results show the beam width of the main lobe of the pattern can reach over 160° with the help of the load on the top of the antenna. And the power of the side-lobe level is very low. In addition, the quadrifitar helix antenna has excellent right-hand circular polarization performance with a beam width of 180°. Both single-frequency and double-frequency communications can be carried out by the antenna in the ranges between 1.2 and 1.8 GHz, with the bandwidth of each frequency about 60 MHz, the simulating and experimental results are nearly the same.
基金supported by the Foundation for Talent Introduction of Guangdong Provincial University,Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme(2008)National Science Foundation of China under Grant No.10971074China Postdoctoral Science Foundation under Grant No.2011M500968
文摘This paper investigates L∞--estimates for the general optimal control problems governed by two-dimensional nonlinear elliptic equations with pointwise control constraints using mixed finite element methods. The state and the co-state are approximated by the lowest order Raviart-Thomas mixed finite element spaces and the control is approximated by piecewise constant functions. The authors derive L∞--estimates for the mixed finite element approximation of nonlinear optimal control problems. Finally, the numerical examples are given.
