  Josephson plasma in RuSr$_{2}$GdCu$_{2}$O$_{8}$,
Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), and
RuSr$_{2}$Eu$_{2-x}$Ce$_{x}$Cu$_{2}$O$_{10}$ (x = 0.5) compounds is
investigated by the sphere resonance method. The Josephson plasma is observed
in a low-frequency region (around 8.5 cm$^{-1}$ at T $\ll$ $T_{c}$) for
ferromagnetic RuSr$_{2}$GdCu$_{2}$O$_{8}$, while it increases to 35 cm$^{-1}$
for non-ferromagnetic Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), which
represents a large reduction in the Josephson coupling at ferromagnetic
RuO$_{2}$ block layers. The temperature dependence of the plasma does not shift
to zero frequency ({\it i.e.} $j_{c}$ = 0) at low temperatures, indicating that
there is no transition from the 0-phase to the $\pi$-phase in these compounds.
The temperature dependence and the oscillator strength of the peak are
different from those of other non-magnetic cuprates, and the origins of these
anomalies are discussed.
