1：Experimental Design and Method Selection:

The study used polysilazane immersion-pyrolysis to synthesize SiC nanotubes on porous Si3N4 matrices. The method involved vacuum immersion of porous Si3N4 matrices in polysilazane followed by pyrolysis at 1100°C, with up to three immersion-pyrolysis cycles. The design aimed to adjust impedance mismatch and enhance absorbing properties by introducing SiC grains into the porous ceramics matrix.

2：Sample Selection and Data Sources:

Porous Si3N4 matrices were prepared using α-Si3N4 powder, Y2O3, Al2O3, and benzoic acid as a pore-forming agent (0–50 wt%). Samples were formed by isostatic pressing and sintered at 1700°C under nitrogen atmosphere. Dielectric properties were measured in the frequency range of 2–18 GHz.

3：List of Experimental Equipment and Materials:

Materials included α-Si3N4 powder (0.5 μm particle size, purity >93%), Y2O3 (purity >99%), Al2O3 (purity >99%), benzoic acid (purity >99%), polysilazane (liquid), paraffin wax (as binder), Si3N4 grinding balls, and absolute methanol. Equipment included ball mill, drying oven, isostatic press, sintering furnace, XRD (EVO-18, CARL ZEISS SMT Ltd), SEM (JSM-6380LA), TEM (JEM-1200EX), and vector network analyzer (VNA, 5244A).

4：5 μm particle size, purity >93%), Y2O3 (purity >99%), Al2O3 (purity >99%), benzoic acid (purity >99%), polysilazane (liquid), paraffin wax (as binder), Si3N4 grinding balls, and absolute methanol. Equipment included ball mill, drying oven, isostatic press, sintering furnace, XRD (EVO-18, CARL ZEISS SMT Ltd), SEM (JSM-6380LA), TEM (JEM-1200EX), and vector network analyzer (VNA, 5244A). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Mixed powders were ball-milled for 15 min, dried, and formed into green specimens by isostatic pressing under 80 MPa for 200 s. Pore-forming agent was removed at 200°C before sintering at 1700°C for 120 min under nitrogen. Porous matrices were immersed in polysilazane under vacuum for 30 min and pyrolyzed at 1100°C, with up to three cycles. Porosity was measured by Archimedes' method, phases identified by XRD, microstructures observed by SEM and TEM, and dielectric properties measured using VNA with samples mixed with paraffin wax (weight ratio 5:2).

5：2). Data Analysis Methods:

5. Data Analysis Methods: Dielectric properties were analyzed using complex dielectric constant (ε = ε′ - jε″), loss tangent (tan ξ = ε″/ε′), reflectivity (R) calculated from transmission line theory, and electromagnetic attenuation coefficient (α) derived from equations based on Debye theory. XRD patterns were compared to JCPDS standards for phase identification.