  We report a study of the microwave conductivity of electron-doped
Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-\delta}$ superconducting thin films using a
cavity perturbation technique. The relative frequency shifts obtained for the
samples placed at a maximum electric field location in the cavity are treated
using the high conductivity limit presented recently by Peligrad $\textit{et}$
$\textit{al.}$ Using two resonance modes, TE$_{102}$ (16.5 GHz) and TE$_{101}$
(13 GHz) of the same cavity, only one adjustable parameter $\Gamma$ is needed
to link the frequency shifts of an empty cavity to the ones of a cavity loaded
with a perfect conductor. Moreover, by studying different sample
configurations, we can relate the substrate effects on the frequency shifts to
a scaling factor. These procedures allow us to extract the temperature
dependence of the complex penetration depth and the complex microwave
conductivity of two films with different quality. Our data confirm that all the
physical properties of the superconducting state are consistent with an order
parameter with lines of nodes. Moreover, we demonstrate the high sensitivity of
these properties on the quality of the films.
