  We propose a new class of oscillators by engineering the dispersion of
two-coupled periodic waveguides to exhibit a degenerate band edge (DBE). The
DBE is an exceptional point of degeneracy (EPD) of order four, i.e.,
representing the coalescence of four eigenmodes of a waveguide system without
loss and gain. We present a distributed DBE oscillator realized in periodic
coupled transmission lines with a unique mode selection scheme that leads to a
stable single-frequency oscillation, even in the presence of load variation.
The DBE oscillator potentially leads to a boost of the efficiency and
performance of RF sources, thanks to the unique features associated to the EPD
concept. This class of oscillators is promising for improving
discrete-distributed coherent sources and can be extended to radiating
structures to achieve a new class of active integrated antenna arrays.
