Analysis Of Millimeter Wave Monopulse Antenna/Feed System

Millimeter wave system has many distinct advantages such as miniaturizing system components, increasing frequency band width, providing higher detectability, not easily influenced by atmosphere conditions, etc. Cassegrain antenna is a kind of dual-reflector antenna, with characteristics of high-gain, narrow-beam, suppressed side lobes and agility in designing. Using simultaneous beam-comparing method, monopulse comparator has good performance in tracking speed, tracking precision and anti-jamming ability. Therefore, such structure with Cassegrain reflector and monopulse comparator is promising in the area of designing tracking radar. In this dissertation, the operation principle and the relations of geometrical parameters of a standard Cassegrain antenna are analyzed by using the geometrical optics method; the equivalent paraboloid method and the aperture field method are used to analyze the antenna's performance based on the equivalent principle; monopulse antennas with four-horn feed and five-horn feed are analyzed respectively by sum-difference signal method; through numerical computation and computer simulation, a tracking system with Cassegrain reflector and monopulse sum-difference network at millimeter wavelengths is finally designed and manufactured; experiments are also carried out.Many kinds of waveguide discontinuities are involved in monopulse sum-difference network, analyses of which have been always essential in designing passive microwave and millimeter wave components. For a long time numerous theoretical and experimental investigations have been applied, and a number of valuable methods, such as variational method, finite element method (FEM), boundary element method (BEM), finite difference time domain method (FDTD), have been published in literatures. The traditional FEM is derived from variational formulation, which has to be determined respectively according to different problems. Here a new FEM arithmetic based on the weak forms of Helmholtz equations is introduced, which is free of these requirements, to deal with waveguide discontinuities. First, the procedure is described, and then the theoretical analysis and numerical calculations of the discontinuities of H-plane waveguide tee junction and H-plane waveguide bend are presented using this technique. Results agree well with those of earlier literatures, and illustrate the accuracy and generality of this approach. These works will become solid groundwork for further analysis and design of sophisticated monopulse sum-difference network.