A characteristic mode analysis of parallel-plate waveguide with finite number of slot as a leaky wav eantenna structure is considered for calculating the characteristics currents, the characteristic patterns, radiatin patterns, and the complex propagation constants. For the cases of 1, 11 and 29 slots, numericl resutls for the equivalent magnetic currents, the radiatin patterns, and thecomplex propagation constants are computed and compared with those obtained by use of the conventional method of moments. Good correspondence between them is observed.