Study On Broadband Antennas With Loadings And Radar Cross Section Of Complex Targets

This thesis puts emphasis on studying input impedance and gain of the vertical loaded antenna, prediction techniques of radar cross section. electrically large and complex targets are studied, which can be missiles or airplanes. In this thesis, we study both the theory and computational techniques for electromagnetic scattering. The author抯 major contributions are as follows: 1. Input impedance, VSWR and gain of the vertical loaded antenna with a LC matching network and an impedance transformer is analyzed by using moment methods. And then, as a example~ a monopole antenna at the center of a circular plane is examined, by using a technique for combining moment methods with the geometrical theory of diffraction, the characteristics of a loaded antenna on a finite ground plane is studied and compared with experimental measurements in the literature. Finally, a experiment is performed~ the numerical results are in agreement with the experimental one. The results demonstrate that this kind of loaded antenna can get good broadband characteristics. 2. SBR is widely-used in RCS computation of cavity scattering. To show its versatility,, this method is used to calculate the RCS of inlet. And the results are in good agreement with the measured data. The technique is easy to integrated with other techniques to evaluate the RCS of complex targets owing to its derivation from the GO method. 3. Back-scattered field of electrically large concave cavity is analyzed with CR method. The complex rays tracing method is developed from radial optics, for the coordinate dimension of the complex space is one time than the real one, the rays tracing is more complex than the real space. The concave cavity with a center-cone is analyzed~ and the results are in good agreement with the measured data. 4. Incremental length diffraction coefficients(ILDC抯) are obtained for the shadow boundaries of perfectly electrically conducting(PEC) convex cylinders of general cross section. First, the nonuniform(NU) current in the vicinity of the shadow boundary is approximated using Fock functions. The product of the approximated current and the free-space Green抯 function is then integrated. This integration is performed in closed form by employing quadratic polynomial approximations for the amplitude and unwrapped phase of the integrated. Finally, as a example, the scattered far field of a PEC sphere is obtained by adding the integral of the NU ILDC抯 of a circular cylinder along the shadow boundary of the sphere to the physical optics(P0) far field of the sphere. This correction to the P0 field is shown to significantly improve upon the accuracy of the P0 far-field approximation in the total scattered field of the sphere. 5. Some key problems on computing the RCS of large and complex targets are investigated., First the model construction of complex targets are discussed. Then demonstrate the computation procedure. Furthermore, a practical algorithm for evaluating scattering of gap is presented. The computation results are in good agreement with the MOM抯 solutions. The discussion of facets noise problem is made...