  Su-Schrieffer-Heeger (SSH) lattices have helped to understand key concepts of
topological insulators. In this paper, we study the transmission properties of
$pn$ junctions of bearded SSH lattices forming a bipartite structure. From a
tight-binding approach, a Bloch Hamiltonian depicts the electron behavior as a
massive pseudo-spin one particle in quasi-one-dimensional systems. It is
possible to design the band structure of these lattices by tuning the on-site
energy and hopping parameters. The characteristic flat band of pseudo-spin one
systems can be bent by the staggered potential of the bottom atom in the
bearded edge. We explore interband transmissions from the bent flat band to the
valence one of a bipartite structure, where Klein tunneling can be obtained
depending on the hopping parameter associated with the bearded edge. The
identification of Klein tunneling signatures is feasible in artificial lattices
such as photonic lattices, elastic resonators, topolectric circuits, or quantum
dot arrangements. On the other hand, the study of Klein tunneling in polyatomic
molecules may contribute to advance in one-dimensional transistors.
