Comments on Controllable Metamaterial Loaded Waveguides Supporting Backward and Forward Waves

Equations (4)
and
(6)

–
(9)
in the above-commented work are not always correct. Here, a general condition for the existence of TE
$_{ {z}}$
and TM
$_{ {z}}$
(i.e., TE and TM waves related to the z-axis) modes in a rectangular waveguide loaded by an anisotropic metamaterial (when the permeability tensor is represented by a diagonal matrix) is presented.