  Terahertz (THz) band is envisioned for the future sixth generation wireless
systems thanks to its abundant bandwidth and very narrow beamwidth. These
features are one of the key enabling factors for high resolution sensing with
milli-degree level direction-of-arrival (DOA) estimation. Therefore, this paper
investigates the DOA estimation problem in THz systems in the presence of two
major error sources: 1) gain-phase mismatches, which occur due to the
deviations in the radio-frequency circuitry; 2) beam-squint, which is caused
because of the deviations in the generated beams at different subcarriers due
to ultra-wide bandwidth. An auto-calibration approach, namely NoisE subspAce
correcTion technique for MUltiple SIgnal Classification (NEAT-MUSIC), is
proposed based on the correction of the noise subspace for accurate DOA
estimation in the presence of gain-phase mismatches and beam-squint. To gauge
the performance of the proposed approach, the Cramer-Rao bounds are also
derived. Numerical results show the effectiveness of the proposed approach.
