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\bibitem{Kroug_etal2001} Kroug, M., Cherednichenko, S., Choumas, M., Merkel, H., Kollberg, E., H{\"u}bers, H. - W., et al. (2001). HEB quasi-optical heterodyne receiver for THz frequencies. In \textit{Proc. 12$^{th}$ Int. Symp. Space Terahertz Technol.} (pp. 244--252). San Diego, CA, USA.

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