In different situations the input reflection coefficient (of a waveguide, of a transmission line etc) is defined differently.
The reflection coefficient may also be established using other field or circuit pairs of quantities whose product defines power resolvable into a forward and reverse wave. For instance, with electromagnetic plane waves, one uses the ratio of the electric fields of the reflected to that of the forward wave (or magnetic fields, again with a minus sign).
So, let's consider for instance a coaxial cable. We may define its input reflection coefficient as the ratio between reverse and the direct travelling voltage waves (V-(z)/V+(z)), but also as the ratio between the reverse and the direct travelling electric fields (E-(z)/E-(z)).
Are these two reflection coefficients the same?