Vivaldi antenna arrays can be designed for operation over 10:1 bandwidths. Simulated results for an infinite array of stripline-fed Vivaldi elements on ɛr=6 substrate performs well for scan to 45° and frequency 1.8-18 GHz. Vivaldi antenna elements are typically 2-3 wavelengths long at the highest frequency of the array. The addition of a properly designed cover (radome) to an array of relatively short Vivaldi antennas can improve its performance over bandwidths on the order of 2:1. Broadside and scanned performance are improved by the cover. Gaps between elements of the array would be desirable so the array can be assembled and repaired by inserting independent modules. However, gaps between the elements cause resonances that destroy the array's wideband performance. The balanced antipodal VIvaldi antenna (BAVA) can be fabricated in modules and by introducing double mirroring, undesirable resonances can be controlled to provide two octaves of frequency operation. The use of Vivaldi antenna arrays for very short pulse systems requires that the antenna not only be well matched over a wide band of frequencies but it must also preserve pulse shape. The dispersive properties of Vivaldi arrays have been investigated and it is found that dielectric substrates, which improve the VSWR bandwidth of the antenna, slightly increase the array's delay dispersion. (6 pages)