Adaptions and improvements to coaxial metal powder filters include distributing a dissipative matrix mixture comprising superconductive material, metal powder, epoxy, and/or magnetic material within a volume defined by an outer tubular conductor and inner conductor. The frequency response of the filter may be tuned by exploiting the energy gap frequency of superconductive material in the dissipative matrix. The inner surface of the outer tubular conductor may be covered with a superconductive material. For a dissipative matrix comprising magnetic material or superconductive powder particles of a certain size, an external magnetic field can be applied to tune the frequency response of the filter.