Several techniques are available to manufacture such filters.
All consist in varying the propagation length with respect to wave frequency. DFs used for matched filtering in receivers are generally amplitude weighted with Taylor or Hamming functions to reduce time sidelobes. A DF is used to generate a LFM chirp. Mixing the return signal with the transmitted reference signal supplies a CW signal whose frequency is a linear function of altitude. A broad range of adaptive signal processing functions are made possible with this equipment.