  Free electrons in the ionosphere lead to significant group delay dispersion
for signals in the megahertz and low gigahertz range. A novel microwave filter
is presented that is capable of compensating for the non-linear ionospheric
dispersion over a 600 MHz bandwidth between 1.2-1.8 GHz. The design method is
general and is not limited to this particular frequency range but can provide
an arbitrary phase and amplitude response over any frequency range. Several of
the filters were constructed and used in an experiment to detect short radio
pulse emission from the lunar regolith.
