The problem of designing a class of m.t.i. filters without the knowledge of the actual shape of the clutter power spectral-density function is considered. The problem is formulated in an appropriate signal space selected for an efficient representation of the clutter signals of specified bandwidth. The optimum transversal filter-weight vector is then chosen to be orthogonal to this space. The approach is shown to yield a min-max filter in a sense to be defined in the paper. The worst-case performance of these filters is analysedand compared with statistically optimum designs used in some other recent papers.