  We present an efficient fabrication method for absorptive microwave filters
based on Eccosorb CR-124. Filters are fabricated from readily available parts
and their cut-off frequency can be set by their length. They exhibit desirable
properties such as a very large and deep stop band with rejection beyond 120 dB
at least up to 40 GHz, more than 10 dB return loss in both the pass and the
stop band as well as an error-function shaped step response without overshoot.
Measurements at very low temperature show that the filters thermalize on a time
scale of the order of 100 s and that they can absorb power as high as 100 nW
with their noise temperature staying remarkably cool, below 100 mK. These
properties make the filters ideal for cryogenic filtering and filtering of IF
port signals of mixers.
