  We present the general conditions to realize a fourth order exceptional point
of degeneracy (EPD) in two uniform (i.e., invariant along z) lossless and
gainless coupled transmission lines (CTLs), namely, a degenerate band edge
(DBE). Until now the DBE has been shown only in periodic structures. In
contrast, the CTLs considered here are uniform and subdivided into four cases
where the two TLs support combinations of forward propagation, backward
propagation and evanescent modes (when neglecting the mutual coupling). We
demonstrate for the first time that a DBE is supported in uniform CTLs when
there is proper coupling between: (i) propagating modes and evanescent modes,
(ii) forward and backward propagating modes, or (iii) four evanescent modes
(two in each direction). We also show that the loaded quality factor of uniform
CTLs exhibiting a fourth order EPD at k=0 is robust to series losses due to the
fact that the degenerate modes do not advance in phase. We also provide a
microstrip possible implementation of a uniform CTL exhibiting a DBE using
periodic series capacitors with very sub-wavelength unit-cell length. Finally,
we show an experimental verification of the existence DBE for a microstrip
implementation of a CTL supporting coupled propagating and evanescent modes.
