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An extremely ultrawideband (UWB) antipodal Vivaldi antenna with a high gain and excellent impedance matching is proposed.An elliptical-shaped director embedded in an exponentially tapered slot is employed to enhance the gain at the high-frequency band, while a metamaterial inspired structure is employed to enhance the gain around center frequency band and the symmetry of the radiation pattern at the low-frequency band. Furthermore, two sets of rectangular slits are symmetrically embedded around the tapered slot to improve the impedance matching at the low-frequency band. Based on this novel structure, an antipodal Vivaldi antenna with good impedance matching and a high gain over an extremely UWB band is successfully designed.The reflection coefficient is lower than −12 dB at 1–4.16 GHz and lower than −16 dB at 4.16–28 GHz. The gain is 4.9–11.6 dBi at 1–8 GHz and higher than 11.6 dBi at 8–28 GHz.
Shi et al. (2021) studied this question.