The fundamental shear horizontal (SH0) wave is widely used for structural health monitoring due to its high detection sensitivity and long propagation range. However, the typical SH0 waves face a trade-off between spatial resolution and signal-to-noise ratio (SNR) when encountering two or more adjacent micro defects. Existing broadband excitation techniques and passive sidelobe suppression methods alone cannot fully overcome the abovementioned challenges. To address these issues, this article proposes an orthogonal complementary spatiotemporal modulation method. First, a spatiotemporal modulation strategy is formulated to generate SH0 waves characterized by a narrow, high-amplitude main lobe, affording a substantial enhancement in spatial resolution with no concomitant degradation in SNR. Second, an active sidelobe suppression method is developed to identify micro defect echoes from macro defect signals by exploiting the complementary radiation characteristics of multiarray acoustic fields. Third, an optimized excitation-reception strategy is presented to realize unilateral reception, thereby further elevating the SNR of micro defect responses. Experimental validation demonstrates that the proposed technique effectively distinguishes a 0.3 mm × 1 mm micro defect located one wavelength away from a macro defect, offering a promising solution for the accurate localization and characterization of submillimeter defect clusters.