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\bibitem{Gao_etal2006} Gao JR, Hiajenius M, Yang ZQ, Klapwijk TM, Miao W, Shi SC, et al. Direct comparison of the sensitivity of a spiral and a twin-slot antenna coupled HEB mixer at 1.6 THz. In: Proc. 17$^{th}$ Int. Symp. Space Terahertz Technol.; 2006. p. 59--62.

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