The major deficiency of conventional ‘balanced antipodal Vivaldi antenna’ (BAVA) is its tilted beam over upper working frequencies. This study reports on a new BAVA to overcome this defect. By applying a dielectric lens in front of the antenna's aperture, beam‐tilting in E‐plane was improved within the ultra‐wideband frequency range, as well as higher frequencies. In the new BAVA, the authors have also achieved an acceptable cross‐polarisation. Measurements show that the antenna has better than 10 dB return loss within the aforesaid frequency range. The measurements successfully verify the simulation results. Group delay and fidelity factor as time domain characteristics of the proposed antenna have been studied. They have compared performance of the conventional BAVA, with achievements of the new BAVA as hereunder.
A method to obtain optimum tradeoffs (Pareto front) between sidelobe level (SLL) and beamwidth (BW) in time domain for ultrawideband (UWB) antenna arrays is presented. Multiobjective particle swarm optimization (MOPSO) is used to deal with these two conflicting objectives. In the optimization process, mutual coupling effects between elements are not considered. However, the multiple solutions obtained from MOPSO enable the designer to consider the mutual coupling effect as an additional constraint. Each element of the array is an antipodal Vivaldi antenna. The optimization template is applied for three different time-domain pattern descriptors. In comparison to arrays with the same number of elements reported in literature, the Pareto fronts obtained in this study provide lower BW and SLL. A four-element sample from resultant Pareto fronts was simulated by using CST Microwave Studio software. This array shows a 13.7-17.2 dBi gain over the whole frequency band from 3-11 GHz, 7.2 BW, and 12 dB SLL for energy pattern.Index Terms-Antipodal Vivaldi antenna, array antenna, multiobjective particle swarm optimization (MOPSO), ultrawideband (UWB) antenna.
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