  We report on temperature-dependent magnetoresistance measurements in balanced
double quantum wells exposed to microwave irradiation for various frequencies.
We have found that the resistance oscillations are described by the
microwave-induced modification of electron distribution function limited by
inelastic scattering (inelastic mechanism), up to a temperature of T*~4 K. With
increasing temperature, a strong deviation of the oscillation amplitudes from
the behavior predicted by this mechanism is observed, presumably indicating a
crossover to another mechanism of microwave photoresistance, with similar
frequency dependence. Our analysis shows that this deviation cannot be fully
understood in terms of contribution from the mechanisms discussed in theory.
