Millimeter-wave filters are essential components in high-frequency systems, serving as spectral gates that isolate desired frequency bands while suppressing unwanted signals. At frequencies extending well above 100 GHz, filter performance becomes extremely sensitive to manufacturing quality. Insertion loss, bandwidth, roll-off characteristics, and achievable Q-factor are all strongly influenced by dimensional accuracy, surface roughness, and the fidelity of internal resonator geometries.
The filters presented in this work were manufactured by Horizon Microtechnologies using a hybrid process that combines micro-precision additive manufacturing with proprietary high-conductivity metallization. The underlying polymer filter bodies were produced using Boston Micro Fabrication’s (BMF) micro-precision 3D printing technology, which enables the fabrication of complex three-dimensional RF structures with dimensional tolerances in the low tens of microns. At mm-wave frequencies, where even small geometric deviations can lead to significant performance degradation, this level of accuracy is critical.
BMF’s micro-AM platform allows intricate resonator cavities, coupling features, and internal geometries to be printed as monolithic structures that are difficult or impossible to realize using conventional machining techniques. This additive approach enables compact, lightweight filter designs while eliminating alignment errors associated with split-block assemblies and multi-part construction. The printed parts exhibit exceptionally smooth internal surfaces, providing an ideal foundation for subsequent metallization.
The same micro-precision additive manufacturing approach also enables compact, board-level RF integration. The metallized RF Filter shown on page 9 was 3D printed using Boston Micro Fabrication’s micro-precision technology and subsequently coated by Horizon Microtechnologies, allowing the structure to be soldered directly onto a PCB. This demonstrates how micro-scale 3D printing supports not only high-performance alternatives to hollow waveguide based filter designs, but also tightly integrated RF assemblies that reduce assembly complexity and simplify system-level integration in millimeter-wave hardware.
Following printing, Horizon applies its proprietary conformal metallization process, producing highly conductive internal surfaces with coating thicknesses exceeding multiple skin depths. This coating preserves the low surface roughness of the printed structures while ensuring uniform conductivity across all internal features, including fine resonators and enclosed cavities. The combination of micro-scale geometric accuracy from BMF’s printing technology and Horizon’s advanced metallization enables filters with very low RF loss and excellent electromagnetic performance.
Using this integrated manufacturing approach, Horizon has produced various mm-wave filters operating across frequencies ranging from 4 GHz to 270 GHz. Measured Q-factors of more than 800 at 260 GHz demonstratethat the combined BMF micro-AM and Horizon metallization process is competitive with high-end conventional manufacturing methods, while offering significant advantages in design freedom, weight reduction, and time to market.
