Wideband Electrically Small Vivaldi Antenna Using Non-Foster Matching

In this letter, an electrically small Vivaldi antenna using active matching is presented for wideband applications. The structure consists of a passive Vivaldi antenna and a non-Foster circuit that is loaded at the feeding port. By generating equivalent positive and negative capacitances, the two parts can achieve conjugated matching over a wide frequency range, which breaks the Bode-Fano limitation in conventional passive matching. The antenna prototype occupies a small size of 0.012λL×0.016λL. The measured -10 dB impedance bandwidth ranges from 120 MHz to 930 MHz. Compared to the passive Vivaldi antenna, the proposed active antenna enhances the gain by about 10 dB.