| The stealth character of aircraft and ships determines the penetration and combat capability of them in modern warfare. The large-scale open-ended cavities, of which the aircraft inlet is the representation, lead to a strong back scattering in the snout direction of the aircraft, which makes the computation of the Radar Cross Section (RCS) of cavity structure significant in the design of stealthy aircrafts. The phased array antenna has become an indispensable component in the advanced radar system for aircraft or naval ship. As a result, the analysis of radiation and scattering fields of the phased array antenna plays an important role in the design of stealthy naval ships. Associated with the research project, this dissertation is mainly concerned with the RCS prediction and control of the cavity structures and phased array antenna systems. The author's major contributions are outlined as follows:1,Pretreatment for RCS computation. Modeling and meshing of the cavities and ships for RCS computation with mixed polygon facets are fulfilled by the applications of the modeling and meshing functions of the Rhinoceros software and a data extraction program. Then, based on the facet models, a study is made of the ray trace technology and shadowing judgment arithmetic.2,Study of the RCS computation algorithms for cavities. An analysis is made firstly of the Iterative Physical Optics (IPO) iterative equation for cavities of the PEC or PEC surface coated with a thin absorber layers. The IPO algorithm is improved as follows. The bottom reflection calculation in the iterative computation is improved firstly, and then, the computation and convergence speed of the IPO algorithm are improved by introducing the initial values succession into the iterative computation, and using the forward-backward iterative and the relaxation factors. The RCS of an inlet model is computed by the developed IPO program, and the results are in good agreement with the experimental ones. Based on the analysis of the precision and computation speed of the RCS computation algorithms for cavities, the dissertation develops the codes of SBR,CRE and IPO parallel algorithms by using MPI, which speeds up the computation while keeping it precise. High efficiency of the parallel algorithms is also achieved by distributing the computation task by big cells.3,The RCS control technology of cavities. The effects of the absorber materials and S-shaping on the RCS of the cavities are studied by using the IPO program. The combination of both methods in RCS control is analyzed. 4,Proposing the FEM/CRE-UTD hybrid method for the computation of the radiation fields of antennas on large carriers. The hybrid method computes the radiation fields of antennas in free space by the finite element method (FEM). After a study of the complex rays expansion of the radiation fields by use of the Fullerence mesh, the reflection effect of the carries on the fields is computed by employing the technologies of complex rays expansion (CRE) of radiation fields, ray trace and complex ray paraxial approximation. Then the diffraction effect of the edges of the carries on the fields is also taken into consideration by adopting the UTD method. As a result, the radiation fields of antennas on large carries are achieved.5,Fast computation of the antenna model scattering fields of antennas using the reciprocity theorem. The antenna model scattering fields of antennas illuminated by a plane wave are computed by using the radiation fields based on the antenna reciprocity theorem. The scattering fields of antennas illuminated by a plane wave at different incident angles can be computed quickly by this method. It can also be combined with the FEM/CRE-UTD hybrid method to compute the antenna model scattering fields of antennas on large ships.6,Study of the radiation and scattering mechanism of array antennas. The couple between the cells of array antennas is analyzed by S parameters of the model of antenna system. The basic theoretical calculation formulae for radiation and scattering of array antennas are deduced by applying spherical wave function expansion and the scattering matrix to the analysis of array antennas. In the formulae, the coupling between the cells and the reflection of the receiver load are taken into consideration, and the relationship between the antenna model scattering fields of the array and the radiation fields of cells is also shown in the formulae. The proposed formulae are still in the superposition form, which makes it possible for the formulae to be simplified to the product theorem by approximation. According to this, an approximate computation method for the radiation fields of large-scale array antennas is studied followed by its validation in the one-dimension array. The characters and peak values of scattering fields are analyzed by the approximation of the basic theoretical calculating formula. After this, the separation and analysis are made of the structural mode scattering and antenna mode scattering of a one-dimension array antennas, which validates the theoretical results.7,Analysis of the radiation and scattering of active phased-array antenna systems. The reflection coefficient of the receiver load of the cell in the array is analyzed by S parameters of the feed systems model of the active phased-array antenna. The approximation computation formula of the antenna mode scattering field is deduced by submitting the reflection coefficient of the receiver load to the basic theoretical formula, which takes the effects of the reflection coefficient of the receiver load and the parameters of the phase shifter into consideration. According to the formula, the antenna model scattering is analyzed by dividing it into two parts. And their characters and the max direction are analyzed and testified in the one-dimension array antenna, which plays a guidance role in the computation of the scattering fields of the phased array and its RCS control.8,RCS control of the phased array antenna on naval ships. Analysis is made of the RCS control technologies for different scattering models of the array antennas. Emphasis is put on the analysis of the effects of array leaning on its radiation and scattering characters, which shows that the side lobe plays an important role in the stealth characters of the array. The array antenna with low side lobe is designed by employing the Taylor synthesis and density taper sparseness with an overall consideration of the radiation and scattering performance. The side lobe of the array antenna is optimized by random search. Finally, a discussion is made about the compact feed system used in the RCS control of array antennas. And based on the left-hand circuit, a compact enhanced-bandwidth hybrid ring is designed.
|
PDF Full Text Request