  We demonstrate the electromagnetic performance of waveguides for femtosecond
electron beam bunch manipulation and compression with strong-field terahertz
(THz) pulses. The compressor structure is a dispersion-free
exponentially-tapered parallel-plate waveguide (PPWG) that can focus
single-cycle THz pulses along one dimension. We show test results of the
tapered PPWG structure using electro-optic sampling (EOS) at the interaction
region with peak fields of at least 300 kV/cm given 0.9 uJ of incoming THz
energy. We also present a modified shorted design of the tapered PPWG for
better beam manipulation and reduced magnetic field as an alternative to a
dual-feed approach. As an example, we demonstrate that with 5 uJ of THz energy,
the PPWG compresses a 2.5 MeV electron bunch by a compression factor of more
than 4 achieving a bunch length of about 18 fs.
