  The first experimental demonstration of an oscillator based on a periodic,
resonant microstrip circuit with a degenerate band edge (DBE) is presented. The
DBE is a fourth-order exceptional degeneracy of the eigenmodes in a lossless
periodic waveguide that is visible in the wavenumber-frequency dispersion
diagram, and the periodic microstrip behaves as a frequency selective medium.
The presence of the DBE condition and the associated DBE resonance allow for a
stable, single-mode oscillation as well as stability with varying the load
resistance.
