Recent research has focused on developing electromagnetic wave absorbers that exhibit high absorption performance, thin thickness, low density, light weight, low cost, and a broad absorption bandwidth. In this study, a virtual model of a polycaprolactone (PCL)-based composite reinforced with varying proportions of nano zinc oxide (ZnO) and silicon dioxide (SiO₂) was developed using COMSOL Multiphysics. A rectangular waveguide structure was designed to simulate a Network Analyzer (NWA) setup used for wave transmission measurements. The complex permittivity of the composites was calculated for different ZnO and SiO₂ contents. The results revealed that the dielectric constant increased from 2.893 to 3.833, and the dielectric loss factor rose from 0.253 to 0.369 with higher filler loading. Consequently, the reflection loss (RL) decreased to 3.718 dB, while the absorption coefficient increased to 0.110, and the attenuation coefficient reached 3.2393 dB at 10 GHz for an absorber thickness of 0.003 m. These findings demonstrate the potential of PCL/ZnO/SiO₂ composites as lightweight and efficient microwave absorbing materials.