Multi-criteria surrogate optimization of the ultrawideband Vivaldi antenna

The article discusses a method for designing an ultrawideband Vivaldi antenna with an operating frequency range from 3 to 8 GHz, which simultaneously satisfies the criteria for matching and stable beamwidth across the entire frequency range with strictly defined antenna dimensions. The initial stage presents the basic topology of a Vivaldi radiator with specified dimensions, obtained in the Antenna Magus package. This modification does not satisfy the matching condition, since some frequencies correspond to VSWR exceeding 2. A modified topology with an internal matching circuit has been presented, which provides better characteristics compared to the original design, but still does not satisfy the VSWR condition across the entire frequency range and has an unstable radiation pattern. Next, a method for optimizing a Vivaldi ultra-wideband antenna using the capabilities of the DT Seven package has been considered. For this purpose, optimization parameters have been formulated, which are the geometric dimensions of some segments of the radiator, and two optimization criteria have been formalized: 1) VSWR value must be less than 2 across the entire operating range from 3 to 8 GHz; 2) the sum of the deviations of the directivity pattern width from the average value across the entire frequency range must be minimal. Based on the selected parameters and optimization criteria, a computational model has been implemented that optimizes the radiator using the target function approximation method (the surrogate model). As a result of optimization, it is possible to achieve a design for which the VSWR value does not exceed 2 across the entire operating frequency band (in the initial configuration, the VSWR value reached a maximum of 3.8). The maximum value of the directivity pattern width across the entire band has been reduced from 220° to 118°. It has been shown that this indicator can be further improved by removing the restrictions on the antenna's dimensions. Thus, the main result of the work is that the developed method for optimizing the Vivaldi antenna allows designing its structure, which simultaneously meets the requirements for matching and the beam width in a wide frequency range at given dimensions.