  Harmonic analysis is a powerful tool to characterize and quantify
current-induced torques acting on magnetic materials, but so far it remains an
open question in studying antiferromagnets. Here we formulate a general theory
of harmonic Hall responses of collinear antiferromagnets driven by
current-induced torques including both field-like and damping-like components.
By scanning a magnetic field of variable strength in three orthogonal planes,
we are able to distinguish the contributions from field-like torque,
damping-like torque, and concomitant thermal effects by analyzing the second
harmonic signals in the Hall voltage. The analytical expressions of the first
and second harmonics as functions of the magnetic field direction and strength
are confirmed by numerical simulations with good agreement. We demonstrate our
predictions in two prototype antiferromagnets, $\alpha-$Fe$_{2}$O$_{3}$ and
NiO, providing direct and general guidance to current and future experiments.
