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\bibitem{Loudkov_etal2005} Loudkov D, Tong C-YE, Blundell R, Kaurova N, Grishina E, Voronov B, et al. An investigation of the performance of the waveguide superconducting HEB mixer at different RF embedding impedances. In: Proc. 16$^{th}$ Int. Symp. Space Terahertz Technol.; 2005. p. 226--9.

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