Low Coefficient of Thermal Expansion (CTE) Ceramic–Thermoplastic Composite for Fused Deposition Modelling of RF and Microwave Devices

Additive manufacturing (AM) has significant potential for rapid prototyping of intricate 3-dimensional geometries, yet its adoption in RF and microwave applications remains limited. Key barriers include inadequate material characterization, high dielectric losses, poor thermal stability, and challenges with multi-material integration. This work addresses these issues by developing a high-k, low-loss composite filament with a reduced coefficient of thermal expansion (CTE), specifically formulated for fused deposition modelling (FDM). By varying filler volume fractions (30%, 40%, and 50% v/v) and surfactant content, their impact on thermal stability and CTE was investigated and measured by thermomechanical analysis (TMA). XRD, Pycnometry, and EDS analysis were performed to verify the effect of the calcination process on ceramic microfillers. The B.E.T. method (Brunauer–Emmet–Teller) was utilized to calculate the specific surface area of the samples with N2 uptake. SEM images of the different composites were presented to visually demonstrate the homogeneous distribution of microfillers in the thermoplastic matrix. Titania was evaluated as the ceramic filler. Titania composites demonstrated decreased CTE values (35.93 ppm/°C at 50% v/v filler coated with surfactant) compared to composites without surfactant. A dielectric waveguide (DWG) printed with the T30S composite achieved an insertion loss of 0.46 dB at 17.23 GHz, significantly outperforming a commercially available ABS450-based DWG (0.95 dB at 16.88 GHz). Measurements aligned closely with 3D electromagnetic simulations, confirming dielectric properties (εr = 5.55, tan δ = 0.0009) suitable for advanced RF and microwave devices and advanced packaging applications.