A chemically etched D-band waveguide orthomode transducer for CMB measurements
Year: 2026
Type: article
Abstract: This study presents a prototype D-band waveguide orthomode transducer (OMT) fabricated using chemically etched brass platelets. This method offers a fast, cost-effective, and scalable approach for producing such devices above 100 GHz, making it well-suited for current and future Cosmic Microwave Background polarization experiments, where large focal planes with thousands of receivers are required to detect the faint primordial B -modes. Chemical etching has already demonstrated its effectiveness in manufacturing corrugated feedhorn arrays with state-of-the-art performance up to 150 GHz. Here, we evaluate its applicability to more complex structures, such as OMTs. We designed a single OMT prototype operating in the 130–170 GHz range, fabricated by chemically etching 0.15 mm-thick brass plates, which were then stacked, aligned, and mechanically clamped. Simulations based on metrological measurements of the OMT profile predict reflected power below −10 dB, cross-polarization better than −30 dB, and transmission around −0.5 dB in the 140−170 GHz band. Measurements yield transmisison around −1.5/−2 dB and cross-polarization $$<-$$ 20 dB. Further simulations show that the degradation in the transmission is related to defects and roughness along the etched profile ( $$\textrm{RMS}\simeq $$ 3 $$\mu $$ m), which is a typical and unavoidable effect of chemical etching. The discrepancy in cross-polarization, instead, could arise from a $$\sim $$ 1.5 $$^{\circ }$$ rotation of the polarization angle within the measurement chain. Our results show that chemical etching is a fast, low-cost, and scalable technique for producing waveguide OMTs with state-of-the-art performance in terms of reflected power and cross-polarization. However, at frequencies above 100 GHz our results show that the mechanical precision limitations of the chemical etching process degrade the transmission coefficient.
Source: Experimental Astronomy
Authors: E. Manzan, A. Mennella, F. Cavaliere, C. Franceschet, S. Mandelli, F. Montonati, M. Zannoni, P. de Bernardis, M. Bersanelli, E. Boria, N. Brancadori, A. Coppolecchia, M. Gervasi, L. Lamagna, A. Limonta, S. Masi, A. Paiella, A. Passerini, F. Pezzotta, G. Pettinari, F. Piacentini, E. Tommasi, D. Viganò, A. Volpe
Institutions: University of Milan, Istituto Nazionale di Fisica Nucleare, Sezione di Milano, Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca, University of Milano-Bicocca, Istituto Nazionale di Fisica Nucleare, Sezione di Roma I, Sapienza University of Rome, Consorzio Roma Ricerche, Agenzia Spaziale Italiana
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $2,590
OpenAlex ID: W7222789247