| Reflector impulse-radiating antennas are good at directional radiate electromagnetic pulses, which have the advantages of narrow main lobe beam, propagation far, high resolution in time and space, and so on. They are widely applied in the areas of directional energy weapons, target detection, imaging, and so on. One of the main difficulties in design of reflector impulse-radiating antennas is that, antenna feed can’t have a fixed phase center in an ultra wide band frequency, while the impulses are usually have rich spectral components. It is common to utilize numerical simulation methods and optimization algorithms to optimize reflector impulse-radiating antennas for obtaining impulses with high peak value and good fidelity in far fields, as well as improving radiation efficiency. However, optimization algorithms usually require calling numerical simulation method for a lot of times when optimizing a reflector impulse-radiating antenna, which will occupy a lot of computation resources and cost expensive time, due to reflector impulse-radiating antennas are electrically large size. Therefore, we devoted to seeking some common approaches for fast design of reflector impulse-radiating antennas in this thesis.Time domain methods for electromagnetic fields calculation are considered to be more appropriate in dealing with ultra wide band impulse problems. Among a lot of time domain methods, the conformal finite difference time domain (CFDTD) method has significant advantage in solving the problems with curved surface, which is suitable for researches on reflector impulse radiating antennas. However, the conformal mesh modeling with manual operations is complicated for various simulation objects. In order to overcome this defect, a robust conformal mesh generation technique for 3-D CFDTD simulation is presented in this paper. Besides, optimization algorithms have been applied in antennas design popularly. The most time-consuming procedure in optimization process is the evaluations of antennas fitness value by calling numerical simulation programs. Therefore, the surrogate models are introduced to reduce the call number of numerical simulation programs in global optimization algorithms, and improve the optimization efficiency.In summary, the main works in this paper are as follows:First, a conformal mesh generation technique based on "Slice-Line Scanning" method is presented for 3-D CFDTD simulation. This mesh generator is capable for dissecting arbitrary 3D multi-material models, with triangle-facet computer aided design files as input data. By improving the "Slice-Line Scanning" method and correction procedures for grids relative area, the equivalent model information on each grid can be determined rapidly and accurately. An antipodal tapered-slot antenna, which is sensitive to its tapered line, was constructed by this mesh generator. The comparisons between simulation and measurement results demonstrate the correctness of this mesh dissection method.Second, the combining approach between Taguchi method and back propagation artificial neural network (BP-ANN), which named BP-based Taguchi method, was studied. The impacts of increasing optimization dimensions and promoting optimization process on the prediction errors of BP-ANN were analyzed by function test. The analysis results show that, in order to make sure the prediction error of BP-ANN can meet the requirements of further optimization, it is necessary to retrain BP-ANN after using this network for certain generations. Three elements of irregular triangular array (3-dimensional), eleven elements of irregular triangular array (6-dimensional), four elements irregular rectangular antenna array (8-dimensional), and an arc tapered transformed-TEM horn (13-dimensional) were optimized, respectively. The optimization results show that, BP-based Taguchi method performed good in reducing the call number of numerical simulation programs when the optimization dimension is less than 8-dimensional, compared with Taguchi method.Third, hybrid-surrogate-model-based efficient global optimization (HSM-based EGO) algorithm was proposed. The Kriging model and radial basis function artificial neural network (RBF-ANN) were employed as the hybrid surrogate model of HSM-based EGO algorithm. Each generation in the optimization process of HSM-based EGO algorithm only requires calling numerical simulation program for three times, which is independent with the optimization dimension. These three new sampling points are selected according to the maximum expected improvement, the minimum sampling density and the local optimal value in solution space, respectively. HSM-based EGO algorithm was applied to a 12-dimensional optimization of a combined-oscillator antenna. Compared to the efficient global optimization (EGO) and the differential evolution strategy (DES), HSM-based EGO algorithm converges to the global optimal value more efficiently.Fourth, an efficient method for determining the ultra wide-band antenna feed’s time-domain approximate radiation center and its corresponding subtended angle was presented, via evaluating the transient radiation patterns of the feed for some given different radiation centers, on the premise of that the antenna feed has been determined, and has mirror symmetry structure. This fast method is helpful to design reflector impulse-radiating antennas to obtain high gain in the bore-sight. The feed-forward reflector impulse-radiating antenna with impedance tapered transformed-TEM horn as feed, Cassegrain impulse-radiating antenna with arc tapered transformed-TEM horn as feed, and single offset reflector impulse-radiating antenna with 2×2 coaxial exponential tapered transformed-TEM horn array as feed were designed by this fast method, respectively. Comparing with the results obtained by sweep parameters and global optimization algorithms, our method is fast and reliable in the design of reflector impulse-radiating antennas.Fifth, a quasi-Gregory impulse-radiating antenna was proposed, based on the structure property of the near field focusing antenna, which has ellipsoidal reflector and natural time-domain approximation radiation center. Gaussian pulses with width 200ps and 330ps were utilized to test the performances of this proposed antenna. The transient subtended angle of its ellipsoidal feed is in accordance with theoretical design and the far-field radiation performance of this quasi-Gregory impulse-radiating antenna is good. The 3-dB beam width of this proposed antenna with 1.5m aperture diameter of the paraboloidal reflector is less than ±3° at H-plane, and less than ±5° at E-plane. This quasi-Gregory impulse-radiating antenna is suitable for radiating pulses in the subnanosecond regime and has good directional performance. |
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