<p>The precise regulation of micro-architecture is a fundamental strategy for modulating the intrinsic physical properties of hard ferrites. In this study, a well-defined circular BaFe₁₂O₁₉ architecture was successfully fabricated through an SDS-assisted hydrothermal-calcination route. The phase composition, morphology evolution, and structural characteristics were systematically investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy, confirming the formation of a highly crystalline hexagonal BaFe₁₂O₁₉ phase with a circular morphology characterized by surface-stacked nanoparticles and residual porosity. The formation mechanism was interpreted based on the combined effects of SDS micellar confinement and crystallographic constraints. Magnetic hysteresis measurements revealed that the circular morphology significantly improves the hard magnetic properties, achieving a coercivity (<i>H</i>_c) of 2934.33 Oe. In addition, the circular architecture modulates the dielectric response behavior of conventional flake-like structures by introducing abundant heterogeneous interfaces and defect sites, which promote multiple polarization relaxation processes. High-frequency electromagnetic measurements further demonstrate that the morphology transition from irregular flakes to circular discs significantly influences the complex permittivity and permeability behavior while improving impedance matching characteristics. The resulting attenuation behavior exhibits a morphology-dependent response in the Ku-band region. This work highlights the important role of morphology engineering in tailoring the high-frequency electromagnetic response of barium ferrite and provides a practical strategy for designing advanced ferrite-based functional materials.</p>