Theoretical $\Sigma$-$D$ Relations for Shell-Type Galactic Supernova
  Remnants
  Relations between radio surface brightness ($\Sigma$) and diameter ($D$) of
supernova remnants (SNRs) are important in astronomy. In this paper, following
the work Duric \& Seaquist (1986) at adiabatic phase, we carefully investigate
shell-type supernova remnants at radiative phase, and obtain theoretical
$\Sigma$-$D$ relation at radiative phase of shell-type supernova remnants at 1
GHz. By using these theoretical $\Sigma$-$D$ relations at adiabatic phase and
radiative phase, we also roughly determine phases of some supernova remnant
from observation data.
