The paper
presents the design of an X-band accelerating section for linearizing
the longitudinal phase space in the Frascati Linac Coherent Light Source
(SPARC). The nine cells structure, operating on the standing wave mode,
is fed by a central coupler and has been designed to obtain a 42 MV/m
accelerating gradient. The 2D profile has been obtained using the electromagnetic
codes Superfish and Oscar2D while the coupler has been designed using
HFSS. Bead-pull measurements made on a copper prototype have been performed
and the results are illustrated and compared with the numerical predictions.