  Using first-principles quantum-transport calculations, we investigate
spin-dependent electronic and transport properties of antiferromagnetic tunnel
junctions (AFMTJs) that consist of (110)-oriented antiferromagnetic (AFM) metal
RuO$_{2}$ electrodes and an insulating TiO$_{2}$ tunneling barrier. We predict
the emergence of a giant tunneling magnetoresistance (TMR) effect in a wide
energy window, a series of barrier layer thicknesses, and different interface
terminations, indicating the robustness of this effect. We show that the
predicted TMR cannot be explained in terms of the global transport
spin-polarization of RuO$_{2}$ (110) but is well understood based on matching
the momentum-dependent spin-polarized conduction channels of the two RuO$_{2}$
(110) electrodes. We predict oscillations of TMR with increasing barrier
thickness, indicating a non-negligible contribution from the perfectly
epitaxial interfaces. Our work helps the understanding of the physics of TMR in
AFMTJs and aids in realizing efficient AFM spintronic devices.
