Dielectric and microwave properties of Cr 2 O 3 -doped aramid/glass fiber hybrid composites

In this study, the electromagnetic properties of neat and 5 wt.% Cr 2 O 3 -doped aramid/glass fiber hybrid epoxy composites were investigated in the 1–20 GHz frequency range for radome and microwave shielding applications. The complex permittivity, reflection ( S 11 ), and transmission ( S 21 ) behaviors were systematically analyzed with and without metallic backing. Results showed that the real permittivity (ε′) decreased with increasing frequency due to Maxwell–Wagner polarization, while Cr 2 O 3 addition reduced both ε′ and dielectric loss (ε″), indicating lower polarization density. Reflection measurements revealed a pronounced resonance in the 8–10 GHz range, with minimum reflection values of approximately −42 dB for the neat composite and −52 dB for the Cr 2 O 3 -doped composite with metallic backing. Additional resonance minima of about −35 to −37 dB were observed at higher frequencies (17–18 GHz). Transmission results indicated S 21 values of approximately −15 to −30 dB for the neat composite and −15 to −28 dB for the Cr 2 O 3 -doped composite, while metallic backing significantly reduced transmission to −45 to −80 dB, reaching values close to −80 dB in the 15–20 GHz range, corresponding to an additional attenuation of about 20–50 dB. Overall, Cr 2 O 3 primarily influenced dielectric behavior and resonance characteristics, whereas the metallic layer dominated electromagnetic attenuation. The findings indicate that the proposed hybrid composites provide a good balance in terms of electromagnetic performance, making them promising candidates for advanced radome structures. Furthermore, their wide transmission bandwidth and tunable electromagnetic behavior suggest potential applicability as conventional composite core in multifunctional antenna systems.