On the Yakubovich Frequency Theorem for linear non-autonomous control processes
with Roberta Fabbri and Russell Johnson,
Discrete Cont. Dyn. Sys. - Ser. A 9 (3) (2003), 677-704.
Using methods of the theory of nonautonomous linear differential systems, namely
exponential dichotomies and rotation numbers, some aspects of Yakubovich's
Frequency Theorem from periodic control systems are generalized to systems with
bounded uniformly continuous coefficients.