A new kind of high permittivity (high-k) and low-loss composite material for fused deposition modeling (FDM) technology based on a cyclo-olefin polymer (COP) thermoplastic matrix embedded with sintered ceramic fillers was developed and characterized up to Ku-band. FDM printed samples made of 30 vol.% COP-MgCaTiO ₂ composites, with filler particles sintered at 1200°C, show a relative permittivity (ε _r ) of 4.82 and a loss tangent (tan δ) below 0.0018. Meanwhile, 3-D-printed samples composed of 25 vol.% COP-Ba _0.55 Sr _0.45 TiO ₃ with particles sintered at 1340°C exhibit a ε _r of 4.92 and a tan δ lower than 0.0114. Also, 30 vol.% COP-TiO ₂ specimens with filler particles sintered at 1200°C exhibit a ε _r of 4.78 and a low tan δ lower than 0.0012, whereas acrylonitrile butadiene styrene-Ba _0.55 Sr _0.45 TiO ₃ specimens with a 6% volume fraction loading of microparticle fillers sintered at 1340°C have demonstrated a ε _r of 3.98 and a tan δ less than 0.0086. Edge-fed microstrip patch antennas operating at 17 GHz were fabricated by a direct digital manufacturing (DDM) approach that combines FDM of electromagnetic composites and microdispensing for deposition of conductive traces and compared with reference designs implemented using commercial microwave laminates regarding antenna size and performance. Evidently, the newly developed ceramic-thermoplastic composites are well suited for microwave device applications up to Ku-band and can be adapted to 3-D printing technologies.

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 (ε_r = 5.55, tan δ = 0.0009) suitable for advanced RF and microwave devices and advanced packaging applications.