The Study And Application Of Hybrid And Fast Method For Radiation And Scattering Problems Of Antennas

On research of complex and electrically large platforms, the analysis of radiation characteristics of antennas and prediction of antennas radar cross section (RCS) has been a difficult issue. This dissertation is mainly concerned with the electromagnetic scattering characteristics of electrically large targets and wide-band analysis of antennas radiating and scattering in the presence of an electrically large conducting platform. The thesis makes use of the method of moments (MoM) combined with physical optics (PO) hybrid method and fast frequency sweep techniques to deal with the above problems. As the base of the following chapter in this thesis, MoM is presented in detail including the particular process of modeling and solving, basis function selection, the resolution of singular matrix. MoM is adopted to deal with the electromagnetic scattering problems of perfectly electric conductor objects in free space and radiation and scattering problems of antennas. MoM is used for the prediction of array antennas RCS with different loading. The planar array antennas RCS is compared with the conformal array antennas RCS.The method of moments-physical optics (MoM-PO) hybrid method is used for the analysis of antennas radiating in the presence of an electrically large conducting platform. The MoM-PO hybrid method and hybrid optimization algorithm is applied to the design of the unequal arrays with the minimum element spacing constraint. The proposed method effectively realizes the suppression of the peak sidelobe level (PSLL) with the mutual coupling.The surface-surface junction model is presented to resolve the wire-surface problems. In order to deal with some drawbacks in the MoM-PO hybrid method, the improved MoM-PO hybrid method is presented in the thesis. For the problem of PO's invalidity to the shadow region, an effective equation is presented to obtain the quick modification of solution in MoM-PO. For the problem of fringe wave, EEC is used to modify the current in the PO region. The improved MoM-PO hybrid method is used for the scattering characteristics analysis of electrically large targets and wide-band analysis of antennas radiating and scattering in the presence of an electrically large conducting platform. So the applied scope of the MoM-PO hybrid method is expanded and the precision is improved.In many practical applications, how to quickly and effectively analyze the electromagnetic scattering characteristic of a target in frequency domains and angular domains is a very interesting problem. The wide-band analysis of antennas radiating and scattering in the presence of an electrically large conducting platform is also in dire need of solving. Firstly, the AWE technique and Maehly approximation are presented. The method of moments (MoM) in conbined with the AWE technique and Maehly approximation is applied to obtain a frequency response and predict monostatic RCS pattern in angular domains of three-dimensional arbitrarily shaped perfectly electric conductor objects, respectively. Numerical results show that the proposed method is superior in terms of CPU time compared to the traditional MoM. Compared to the AWE technique, the major advantage of the Maehly approximation is that it can avoid computing derivatives of the dense impedance matrix and excitation matrix, and it is accurate in much broader frequency band. It can be easily implemented into an existing MoM and MoM-PO hybrid method computer code. Compared with the AWE technique, the Maehly approximation is accurate in much broader frequency domains and angular domains. Good agreement between MoM combined with Maehly approximation and the traditional MoM is observed. The MoM-PO hybrid method combined with Maehly approximation is introduced to analyze the input impedance and return loss of antennas in the presence of an electrically large conducting platform. The applied scope of MoM-PO hybrid method is further extended. In many practical applications, it is desirable to predict the monostatic RCS of a target in both the frequency domains and angular domains simultaneously. Although the Maehly approximation is accurate and efficient, it is difficult to apply this method for the approximation of three-dimensional RCS pattern. As a result, we expand the Maehly approximation into two-dimensional extrapolation technique. The best uniform rational approximation combined with MoM is proposed to calculate quickly the three-dimensional RCS pattern of three-dimensional arbitrarily shaped perfectly electric conductor objects and array antennas in frequency domains and angular domains. The applied scope of Maehly approximation is further extended.