  In fabricating the first X-Band RDDS (Rounded Damped Detuned Structure)
accelerator structure, microwave measurements are made on short groups of discs
prior to bonding the discs of the entire structure. The design dispersion
curves are compared with the frequency measurements. The theory utilised is
based on a circuit model adapted to a short stack of slowly varying non-uniform
discs. The model reveals the nature of the modes in the structure and may also
be used to refit the experimental data to the parameters in a model of the
wakefield given earlier [1]. This method allows a more faithful determination
of the wakefield that a beam will experience as it traverses the structure.
Results obtained on the frequencies are compared to the original design.
  [1] R.M.Jones, et al, EPAC96 (also SLAC-PUB-7187)
