An analysis of the feeding system geometry influence on the frequency and directivity characteristics of an unbalanced Vivaldi antenna. Abstract.

Abstract. The results of a numerical electromagnetic simulation of an unbalanced Vivaldi element are presented. The study is devoted to the analysis of a feeding scheme geometry (designed in the form of a radial stripline stub) influence upon the directivity and frequency parameters: resonant frequencies, best input impedance matching frequencies, input impedance matching frequency bands, sidelobe levels, mainlobe beamwidths, antenna gain. It was found that the antenna gain, provided by the geometry under consideration, is weakly sensitive to the deviations of a radial stub flare angle form 0° to 100° and angular displacement from 30° to 120° and equals to 10 dB. In the tuning range of both angles form 0° to 110° the lowest possible, almost constant and equal to -10 dB sidelobe level is achieved. For an angular displacement of a radial stub up to 110° and flare angle deviations up to 120° the mainlobe half-power beamwidths stays practically constant and equal to its minimum value of 70°. It was observed that the initial feeding geometry provide the best possible directivity characteristics but is far from optimal for frequency characteristics and matching the antenna with the input signal source. In particular the antenna is effectively matched with the input source for almost all radial stub flare angles under consideration. Nevertheless the radial stub flare angle diminishing by 10° can possibly yield input source matching improvement up to 19 dB and angular displacement diminishing by the same value delivers up to 11 dB. Hereby it was demonstrated that such a feeding geometry can be effectively utilized to synthesize an ultra-wideband antenna with mechanical steering of the feeding radial stripline stub parameters yielding 10 dB gain, -10 dB sidelobe level and high input signal source matching for different frequency subbands.

Key words: Vivaldi antenna, feeding geometry, input matching, side-lobe level, gain, analysis, simulation.

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