Broadband scanning arrays require small element spacing over a broad frequency band to achieve the desired scan capabilities. Previous research has concentrated on the development of small broadband elements to meet the demands of broadband arrays. However, mutual coupling between elements in a tightly spaced array can change the operating frequency and bandwidth from that of the single isolated element. Several research efforts have focused on minimizing the mutual coupling to maintain the frequency response of the single isolated element. This dissertation focuses on using the strong coupling between Foursquare antennas to obtain the broadband frequency response while maintaining a small element spacing. The isolated Foursquare antenna was modeled using an in-house FDTD code. The modeled current distribution over the frequency band of operation revealed how the antenna achieved a broadband frequency response. Because of this understanding of the single element, the downward shift in the frequency response of the Foursquare antenna in a fully active array could be anticipated. Furthermore, the infinite array models of the Foursquare revealed an increase in bandwidth. Both are desirable characteristics for a broadband scanning array. Therefore, through this research using the Foursquare element, it has been shown that the strong mutual coupling in a tightly spaced array can have advantages if initially taken into consideration when designing the array. / Ph. D.