Mutual coupling between the waveguides in finite arrays has been analyzed by using the integral equation method. Numerical solutions are obtained from which we find that the coupling in general decreases with the wavelength, as well as the distance s between the waveguides, and that for large separations the rate of decrease is inversely proportional to s½. However, when the waveguides are loaded with dielectric plugs, the characteristics of coupling may be substantially changed, owing to the excitation of modes that are propagating inside the dielectric but evanescent in the empty waveguide region. For example, the coupling may be greatly enhanced or suppressed depending on the choice of parameters such as the dielectric constant and plug thickness. In particular, it is found that under suitable conditions the coupling can exhibit resonance characteristics.