Development and Characterization of a Prototype Cosmic Microwave Background Calibration Target

The capability to construct devices that have low reflectance (and high absorptivity) of electromagnetic radiation at long wavelengths has many potential applications ranging from radar evasion to EMI control to calibration of sensitive detectors for cosmology. In cosmology, characterization of the spectrum and polarization of the cosmic microwave background, the afterglow of the Big Bang, requires measurements that are accurate to one part in 10⁷. We describe the fabrication of a prototype cosmic microwave background calibration target that consists of an array of 169 cones, each constructed of loaded epoxy that is molded around an aluminum core for mechanical attachment and thermal stability. By testing the target over a range of frequencies, we achieved a reflectance of -50 dB. These processes were developed as a key technology to support a future NASA space mission to measure the spectrum and polarization of the cosmic microwave background to probe the physics of the early universe.