A numerical study is made of the bandwidth to thickness ratio of radar absorbers for the suppression of normally incident waves. The study deals with single- and multi-layer dielectric absorbers, in which the frequency dispersion of the permittivity is allowed for. Analysis of the results permits obtaining a simple empirical relationship between thickness, bandwidth, and reflectance level of some specific kinds of absorbers. Essential features of different designs of dielectric radar absorbers are revealed and discussed.