This work presents an array of 77 corrugated feed horns coupled with waveguide orthomode transducers (OMTs), operating in the 200−280 GHz band. The prototypes are realized in aluminum by combining the platelet and laser micro-machining techniques. Compared with more conventional approaches (Electroforming, Electric Discharge Machining (EDM), or Micromilling), this technique combines low cost and high scalability, enabling large-scale manufacturing. This is essential for Cosmic Microwave Background (CMB) polarization experiments, which require large focal planes with thousands of detectors to target primordial B-modes. The corrugated feed horns were designed to achieve performance level of typical CMB instruments, with simulated cross-polarization ≤ −25 dB and sidelobe levels ≤ −25 dB. For the OMTs, we implemented a turnstile-junction architecture, achieving a high polarization discrimination capability, with simulated cross-polarization ≤ −60 dB. The aluminum platelets, with thicknesses between 0.050mm and 0.300 mm, were laser-machined, then pin-aligned and mechanically clamped. Metrological measurements show smooth profiles (rms roughness of 2 μm on rectangular holes) and accurate engraving of both rectangular and circular features: deviations are zero-centered with ∼ 68% within 19 μm for rectangular holes, and centered at 3 μm with ∼ 68% within 21 μm for circular holes. A systematic shift of the geometry centers, attributed to thermal expansion during laser machining, results in relative rms misalignment of 16 μm (x) and 10 μm (y) for the horn and of 33 μm (x) and 18 μm (y) for the OMT. Simulations incorporating metrological results show no notable impact on the horn performance. For the OMT the main effects are a degradation of the return loss which remain below −15 dB, and an increase in the cross polarization and isolation levels, which sets around −25 dB, values still suitable for the applications of these devices to CMB polarization experiments. These results are currently being validated through ongoing radio-frequency measurements.
Brancadori, N., Boria, E., Cavaliere, F., Franceschet, C., Manzan, E., Mennella, A., et al. (2026). Laser-micromachined aluminum platelets applied to high-frequency microwave passive components for CMB applications. In Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XIII SPIE Astronomical Telescopes + Instrumentation [10.1117/12.3101762].
Laser-micromachined aluminum platelets applied to high-frequency microwave passive components for CMB applications
Gervasi, M.;Passerini, A.;Zannoni, M.
2026
Abstract
This work presents an array of 77 corrugated feed horns coupled with waveguide orthomode transducers (OMTs), operating in the 200−280 GHz band. The prototypes are realized in aluminum by combining the platelet and laser micro-machining techniques. Compared with more conventional approaches (Electroforming, Electric Discharge Machining (EDM), or Micromilling), this technique combines low cost and high scalability, enabling large-scale manufacturing. This is essential for Cosmic Microwave Background (CMB) polarization experiments, which require large focal planes with thousands of detectors to target primordial B-modes. The corrugated feed horns were designed to achieve performance level of typical CMB instruments, with simulated cross-polarization ≤ −25 dB and sidelobe levels ≤ −25 dB. For the OMTs, we implemented a turnstile-junction architecture, achieving a high polarization discrimination capability, with simulated cross-polarization ≤ −60 dB. The aluminum platelets, with thicknesses between 0.050mm and 0.300 mm, were laser-machined, then pin-aligned and mechanically clamped. Metrological measurements show smooth profiles (rms roughness of 2 μm on rectangular holes) and accurate engraving of both rectangular and circular features: deviations are zero-centered with ∼ 68% within 19 μm for rectangular holes, and centered at 3 μm with ∼ 68% within 21 μm for circular holes. A systematic shift of the geometry centers, attributed to thermal expansion during laser machining, results in relative rms misalignment of 16 μm (x) and 10 μm (y) for the horn and of 33 μm (x) and 18 μm (y) for the OMT. Simulations incorporating metrological results show no notable impact on the horn performance. For the OMT the main effects are a degradation of the return loss which remain below −15 dB, and an increase in the cross polarization and isolation levels, which sets around −25 dB, values still suitable for the applications of these devices to CMB polarization experiments. These results are currently being validated through ongoing radio-frequency measurements.
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