The electromagnetic fields and plasma parameters were studied in an azimuthally symmetric planar-type SWP source employing multiring slot antenna (MRSA), by using a two-dimensional numerical simulation based on the finite-difference time-domain (FDTD) approximation to Maxwell's equations self-consistently coupled with a fluid model for plasma evolution. The calculation was conducted for different four types of MRSA consisting of six coaxial metal rings implanted in a dielectric plate. It was shown that the radial uniformity of plasma is remarkably improved by varying the axial thickness of the six rings with location; the most uniform plasma distribution was obtained for the MRSA with the center two rings 0.25 cm in thickness and outlying four rings 1.6 cm in thickness. (c) 2005 Elsevier B.V. All rights reserved.