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Ekstrom, H., Karasik, B., Weikle, R., Yngvesson, K. S., Gol’tsman, G., Kollberg, E., et al. (1993). Mixers using superconducting Nb films in the resistive state. In 23rd European Microwave Conf. (pp. 787–789).
Abstract: The mixing of 20 GHz radiation in a Nb superconducting film in the resistive state was studied. The experiment gave evidence of electron-heating to be the origin of the non-linear phenomenon. The requirements on the operation mode and on the film parameters in order to obtain small conversion losses or even gain are determined. Our measurements indicate a conversion loss of about 6-8 dB. The hot-electron bolometer is considered to be very promising for use in heterodyne receivers in a wide frequency range from microwaves to terahertz frequencies.
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Ekström, H., Kollberg, E., Yagoubov, P., Gol'tsman, G., Gershenzon, E., & Yngvesson, S. (1997). Phonon cooled ultra thin NbN hot electron bolometer mixers at 620 GHz. In Proc. 8th Int. Symp. Space Terahertz Technol. (pp. 29–35).
Abstract: We have measured the noise performance and gain bandwidth of 35 A thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. A double-sideband receiver noise temperature less than 1300 K has been obtained with a 3 dB bandwidth of GHz. The gain bandwidth is 3.2 GHz. A lower noise temperature of 1100 K has been achieved with an improved set-up. The mixer output noise dominated by thermal fluctuations is about 50-60 K, and the SSB receiver and intrinsic conversion gain is about -18 and -12 dB, respectively. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K.
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Ekström, H., Kroug, M., Belitsky, V., Kollberg, E., Olsson, H., Goltsman, G., et al. (1996). Hot electron mixers for THz applications. In E. J. Rolfe, & G. Pilbratt (Eds.), Proc. 30th ESLAB (pp. 207–210).
Abstract: We have measured the noise performance of 35 A thin NbN HEB devices integrated with spiral antennas on antireflection coated silicon substrate lenses at 620 GHz. From the noise measurements we have determined a total conversion gain of the receiver of—16 dB, and an intrinsic conversion of about-10 dB. The IF bandwidth of the 35 A thick NbN devices is at least 3 GHz. The DSB receiver noise temperature is less than 1450 K. Without mismatch losses, which is possible to obtain with a shorter device, and with reduced loss from the beamsplitter, we expect to achieve a DSB receiver noise temperature of less ‘than 700 K.
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Elant'ev, A. I., & Karasik, B. S. (1989). Effect of high-frequency current on Nb superconductive film in resistive state. Sov. J. Low Temp. Phys., 15(7), 379–383.
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Elantev, A. I., & Karasik, B. S. (1994). Noise temperature of a superconducting hot-electron mixer. In Proc. 5th Int. Symp. Space Terahertz Technol. (225).
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