A stacked-patch reduced surface wave antenna

The reduced surface wave (RSW) microstrip antenna (Jackson, D.R. et al., IEEE Trans. Antennas and Propagat., vol.41, no.8, p.1026-37, 1993; Khayat, M.A. et al., IEEE Trans. Antennas and Propagat., vol.48, no.10, p.1581-93, 2000) is a modified annular-ring patch that has the inner boundary short-circuited to the ground (therefore it is called a "shorted annular-ring RSW", SAR-RSW, antenna). By appropriately choosing the outer radius, the dominant mode of the antenna excites no surface-wave fields. Consequently, RSW microstrip antennas launch very little surface-wave fields, and also have very little lateral (near-horizon) radiation. As a result, such antennas may be attractive for array applications, to reduce mutual coupling and scan blindness. However, the size of the RSW antenna introduced by Jackson et al. is fairly large. For a thin substrate, the diameter is about 0.6/spl lambda//sub 0/, and this does not change significantly with the substrate dielectric constant. For array and other applications, an RSW antenna of smaller size would be desirable. A new type of RSW microstrip antenna is proposed, to reduce the size. The antenna is a stacked-patch RSW antenna.