  We experimentally demonstrate for the first time the degenerate band edge
(DBE) condition, namely the degeneracy of four Bloch modes, in loaded circular
metallic waveguides. The four modes forming the DBE represent a degeneracy of
fourth order occurring in a periodic structure where four Bloch modes, two
propagating and two evanescent, coalesce. It leads to a very flat
wavenumber-frequency dispersion relation, and the finite length structure's
quality factor scales as $N^5$ where $N$ is the number of unit cells. The
proposed waveguide in which DBE is observed here is designed by periodically
loading a circular waveguide with misaligned elliptical metallic rings,
supported by a low-index dielectric. We validate the existence of the DBE in
such structure using measurements and we report good agreement between
full-wave simulation and the measured response of the waveguide near the DBE
frequency; taking into account metallic losses. We correlate our finding to
theoretical and simulation results utilizing various techniques including
dispersion synthesis, as well as observing how quality factor and group delay
scale as the structure length increases. Moreover, the reported geometry is
only an example of metallic waveguide with DBE: DBE and its characteristics can
also be designed in many other kinds of waveguides and various applications can
be contemplated as high microwave generation in amplifiers and oscillators
based on an electron beam interaction or solid state devices, pulse compressors
and microwave sensors.
