  Space-time reflection symmetry (PT symmetry) in non-Hermitian electronic
models has drawn much attention over the past decade mainly because it
guarantees that the band structures calculated under open boundary conditions
be the same as those calculated under periodic boundary conditions. PT symmetry
in electromagnetic (EM) models, which are usually borrowed from electronic
models, has also been of immense interest mainly because it leads to
'exceptional' parameter values below which non-Hermitian operators have real
eigenvalues, although PT symmetry is not the sole symmetry which allows such
exceptional parameter values. In this article, we examine one-dimensional
PT-symmetric non-Hermitian EM models to introduce novel concepts and phenomena.
We introduce the band-structure concept of 'fixed points', which leads to
'bidirectional' reflection zeros in the corresponding finite structures,
contrary to a common belief about the EM structures with PT symmetry (and
without P and T symmetries). Some of the fixed points manifest themselves as
what we name 'extended states in the bandgap' on the band structure while some
other fixed points are the 'turning points' of the band structure. The extended
states in the band gap are in fact the dual of the well-known 'bound states in
the continuum' while the turning points allow us to observe 'ideal'
superluminal tunneling in the corresponding finite structures. By 'ideal'
superluminal tunneling we mean the case where not only the transmission
coefficient has an almost uniform phase over a broad bandwidth but also the
magnitudes of the transmission and reflection coefficients are almost equal to
unity and zero, respectively, over the bandwidth.
