Polytetrafluoroethylene (PTFE)-based composites are widely in demand for microwave substrate application due to their excellent dielectric properties and low power loss. In this work, PTFE matrix filled with different contents (5 wt.% – 25 wt.%) of soda lime silica (SLS) glass powder were prepared and fabricated via dry powder processing technique. The SLS glass powder was acquired through milling process. X-ray diffraction (XRD) was used to characterise the composites for phase identification. In addition, dielectric properties of the composites were measured using open-ended coaxial probe (OCP) technique at 1 GHz to 12 GHz microwave frequencies. The XRD pattern of the composites confirmed the phase of PTFE and highlighted the interaction between the PTFE and SLS phases. The results, also, revealed that relative permittivity (ε') and loss tangent (tanδ) decrease with frequency, while they appreciate with the SLS filler content. Furthermore, the composites exhibited optimum dielectric properties at 10 GHz for 10 wt.% SLS filler with ε' and tanδ values of 2.23 and 0.0011, respectively. This result was favourably compared with some reported PTFE-based composites characterised using other methods, thereby, indicating the suitability of OCP technique for characterising solid dielectric materials for microwave substrate application.