Mutual coupling between reduced surface wave antennas in an array

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 (see Jackson, D.R. et al., IEEE Trans. Antennas and Propagation, vol.41, no.8, 1993). The mutual coupling between a pair of shorted annular ring (SAR) RSW antennas was studied theoretically and experimentally (see Khayat, M.A. et al., IEEE Trans. Antennas and Propagation, vol.48, no.10, 2000). The study showed that the E-plane mutual coupling between RSW antennas fell off as 1//spl Delta//sup 3/ (for thin substrates), where /spl Delta/ 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//spl Delta/ (for thin substrates). The weak mutual coupling property makes a RSW array design very promising. The mutual coupling between RSW elements in an array with an arbitrary lattice angle /spl alpha/ is considered. Specifically, the mutual coupling in an equilateral triangular lattice (/spl alpha/=60/spl deg/) and a square lattice (/spl alpha/=90/spl deg/) 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.