The phenomenon of the resonant reflection of a train of monochromatic waves by an undulated bottom has been largely studied, but in most cases within the hypothesis of smooth variations of the bottom behaviour. Here we consider the case of a series of equally spaced submerged breakwaters of rectangular section, in order to investigate the role of the evanescent modes, neglected in the previous studies, and to evaluate the response of a structure that could be of interest from an engineering point of view. It has been found that the resonant reflection does not occur only in correspondence with the waves of length twice the wavelength of the Fourier components of the bottom behaviour, but also in correspondence with waves of the same length as the distance between the breakwaters. Furthermore, the strength of the resonant reflections,i.e. the height and width of the peaks in the response curve, seems to depend merely on the total amount of material employed in the construction of the breakwaters.