  Dielectric-loaded accelerating (DLA) structures are being studied as an
alternative to conventional disk-loaded copper structures to produce the high
accelerating gradient. This paper presents the design, fabrication and
low-power RF measurement of an externally-powered X-band DLA structure with a
dielectric constant epsilon_r=16.66 and a loss tangent tan_delta=0.0000343. A
dielectric matching section for coupling the RF power from a circular waveguide
to an X-band DLA structure consists of a very compact dielectric disk with a
width of 2.035 mm and a tilt angle of 60 degree, resulting in a broadband
coupling at a low RF field which has the potential to survive in the high-power
environment. Based on simulation studies, a prototype of the DLA structure was
fabricated. Results from bench measurements and their comparison with design
values are presented. The detailed analysis on the fabrication error which may
cause the discrepancy between the RF measurements and simulations is also
discussed.
