  We study conditions for the abstract periodic linear functional differential
equation $\dot{x}=Ax+F(t)x_t+f(t)$ to have almost periodic with the same
structure of frequencies as $f$. The main conditions are stated in terms of the
spectrum of the monodromy operator associated with the equation and the
frequencies of the forcing term $f$. The obtained results extend recent results
on the subject. A discussion on how the results could be extended to the case
when $A$ depends on $t$ is given.
