In 1993 Beggs et al. [202] used the FDTD method to analyze the radiation from shaped-end radiators, while Maeshima et al. [203] investigated a 2-D cavity backed antenna. Toland et al. [128] and Thomas et al. [132] have investigated active antennas using the FDTD method. In 1994, Penney and Luebbers [204,205] analyzed both square and semi-circular spiral antennas using the FDTD method, while recently Shum and Luk [206,207,208] analyzed aperture coupled dielectric resonator antennas.