  We consider the implications of the small Fermi surface for the ab-plane
microwave absorption. The small Fermi surface results in two superconducting
condensates. Linear combinations of these condensates correspond to the d- and
g-wave pairings. Microwave electric field applied in the ab-plane induces
Josephson transitions between the condensates. Dependence of the absorption
upon direction, amplitude and frequency of the external microwave field is
calculated. Results of the calculation are compared with the observed recently
novel non-linear phenomena in microwave absorption of $YBaCu_2O_{7-\delta}$
single crystals.
