  We present new measurements of the millimeter wavelength continuum emission
from the long period variable Mira ($o$ Ceti) at frequencies of 46 GHz, 96 GHz,
and 229 GHz ($\lambda$~7 mm, 3 mm, and 1 mm) based on observations obtained
with the Jansky Very Large Array (JVLA) and the Atacama Large
Millimeter/submillimeter Array (ALMA). The measured millimeter flux densities
are consistent with a radio photosphere model derived from previous
observations, where flux density, $S_{\nu}\propto\nu^{1.86}$. The stellar disk
is resolved, and the measurements indicate a decrease in the size of the radio
photosphere at higher frequencies, as expected if the opacity decreases at
shorter wavelengths. The shape of the radio photosphere is found to be slightly
elongated, with a flattening of ~10-20%. The data also reveal evidence for
brightness non-uniformities on the surface of Mira at radio wavelengths. Mira's
hot companion, Mira B was detected at all three observed wavelengths, and we
measure a radius for its radio-emitting surface of $\approx2.0\times10^{13}$
cm. The data presented here highlight the power of the JVLA and ALMA for the
study of the atmospheres of evolved stars.
