Reduced Surface Wave (RSW) antennas produce only a small amount of surface-wave and lateral-wave radiation since the surface-wave and lateral-wave radiation from the dominant TM{sub}(011) patch mode is suppressed through proper design [1]. The mutual coupling between a pair of Shorted Annular Ring (SAR) RSW antennas was studied theoretically and experimentally [2]. The study showed that the F-plane mutual coupling between RSW antennas fell off as 1/Δ{sup}3 (for thin substrates), where Δ is the center-to-center separation between the antennas. This is a much faster falloff than for conventional microstrip antennas, where the E-plane mutual coupling decays as 1/Δ (for thin substrates). The weak mutual coupling property makes a RSW array design very promising. In this paper, the mutual coupling between RSW elements in an array with an arbitrary lattice angle α is considered. Specifically, the mutual coupling in an equilateral triangular lattice (α= 60°) and a square lattice (α = 90°) are studied. Two feeding methods, E-plane feeding and a rotated feeding are considered and results are compared with those of a conventional circular microstrip array. The grating lobe issue is also studied for different lattice angles.
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