  We obtain necessary and sufficient conditions for the existence of strictly
stationary solutions of ARMA equations in Banach spaces with independent and
identically distributed noise under certain assumptions. First, we obtain
conditions for ARMA(1,$q$) equations by excluding zero and the unit circle from
the spectrum of the operator of the AR part. We then extend this to
ARMA($p$,$q$) equations. Finally, we discuss various examples.
