A wire cookie cooler is used as the beam splitter in a microwave Michelson interferometer. Two aluminum plates function as the mirrors on the two legs. As either of the plates is moved along the optic axis the intensity of the beam at the location of the receiving antenna varies, with the intensity displayed on an overhead projector meter. The wavelength of the microwaves is about 12 cm, so a change of about three cm is required for the two beams to change in or out of phase.
The sequence of pictures above show the reflector at the right being withdrawn by intervals of one-quarter wavelength, resulting in alternating minima and maxima of the recombined microwave beam at the location of the receiving antenna.