Electromagnetic Design of Feedhorn-Coupled Transition-Edge Sensors for Cosmic Microwave Background Polarimetry

• Published in: Journal of low temperature physics 2012-06, Vol.167 (5-6), p.923-928
• Main Authors: Chuss, D. T., Bennett, C. L., Costen, N., Crowe, E., Denis, K., Eimer, J. R., Lourie, N., Marriage, T. A., Moseley, S. H., Rostem, K., Stevenson, T. R., Towner, D., U-Yen, K., Voellmer, G., Wollack, E. J., Zeng, L.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Magnetic Materials; Magnetism; Physics; Physics and Astronomy
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/s10909-011-0433-2

Observations of the cosmic microwave background (CMB) provide a powerful tool for probing the evolution of the early universe. Specifically, precision measurement of the polarization of the CMB enables a direct test for cosmic inflation. A key technological element on the path to the measurement of this faint signal is the capability to produce large format arrays of background-limited detectors. We describe the electromagnetic design of feedhorn-coupled, TES-based sensors. Each linear orthogonal polarization from the feedhorn is coupled to a superconducting microstrip line via a symmetric planar orthomode transducer (OMT). The symmetric OMT design allows for highly-symmetric beams with low cross-polarization over a wide bandwidth. In addition, this architecture enables a single microstrip filter to define the passband for each polarization. Care has been taken in the design to eliminate stray coupling paths to the absorbers. These detectors will be fielded in the Cosmology Large Angular Scale Surveyor (CLASS).