|
Merkel, H. F., Khosropanah, P., Sigfrid Yngvesson, K., Cherednichenko, S., Kroug, M., Adam, A., et al. (2001). An active zone small signal model for hot-electron bolometric mixers. In Proc. 12th Int. Symp. Space Terahertz Technol. (55). San Diego, CA, USA.
|
Cherednichenko, S., Kroug, M., Khosropanah, P., Adam, A., Merkel, H., Kolberg, E., et al. (2002). A broadband terahertz heterodyne receiver with an NbN HEB mixer. In Harward University (Ed.), Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 85–95). Cambridge, MA, USA.
Abstract: We present a broadband and low noise heterodyne receiver for 1.4-1.7 THz designed for the Hershel Space Observatory. A phonon- cooled NbN HEB mixer was integrated with a normal metal double- slot antenna and an elliptical silicon lens. DSB receiver noise temperature Tr was measured from 1 GHz through 8GHz intermediate frequency band with 50 MHz instantaneous bandwidth. At 4.2 K bath temperature and at 1.6 THz LO frequency Tr is 800 K with the receiver noise bandwidth of 5 GHz. While at 2 K bath temperature Tr was as low as 700 K. At 0.6 THz and 1.1 THz a spiral antenna integrated NbN HEB mixer showed the receiver noise temperature 500 K and 800 K, though no antireflection coating was used in this case. Tr of 1100 K was achieved at 2.5 THz while the receiver noise bandwidth was 4 GHz.
|
Cherednichenko, S., Kollberg, E., Angelov, I., Drakinskiy, V., Berg, T., & Merkel, H. (2005). Effect of the direct detection effect on the HEB receiver sensitivity calibration. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 235–239). Göteborg, Sweden.
Abstract: We analyze the scale of the HEB receiver sensitivity calibration error caused by the so called “direct detection effect”. The effect comes from changing of the HEB parameters when whey face the calibration loads of different temperatures. We found that for HIFI Band 6 mixers (Herschel Space Observatory) the noise temperature error is of the order of 8% for 300K/77K loads (lab receiver) and 2.5% for 100K/10K loads (in HIFI). Using different approach we also predict that with an isolator between the mixer and the low noise amplifiers the error can be much smaller.
|
Khosropanah, P., Merkel, H., Yngvesson, S., Adam, A., Cherednichenko, S., & Kollberg, E. (2000). A distributed device model for phonon-cooled HEB mixers predicting IV characteristics, gain, noise and IF bandwidth. In Proc. 11th Int. Symp. Space Terahertz Technol. (pp. 474–488). University of Michigan, Ann Arbor, MI USA.
Abstract: A distributed model for phonon-cooled superconductor hot electron bolometer (HEB) mixers is given, which is based on solving the one-dimensional heat balance equation for the electron temperature profile along the superconductor strip. In this model it is assumed that the LO power is absorbed uniformly along the bridge but the DC power absorption depends on the local resistivity and is thus not uniform. The electron temperature dependence of the resistivity is assumed to be continuous and has a Fermi form. These assumptions are used in setting up the non-linear heat balance equation, which is solved numerically for the electron temperature profile along the bolometer strip. Based on this profile the resistance of the device and the IV curves are calculated. The IV curves are in excellent agreement with measurement results. Using a small signal model the conversion gain of the mixer is obtained. The expressions for Johnson noise and thermal fluctuation noise are derived. The calculated results are in close agreement with measurements, provided that one of the parameters used is adjusted.
|
Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Gol'tsman, G., Svechnikov, S., et al. (1998). Noise temperature and local oscillator power requirement of NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies. Appl. Phys. Lett., 73(19), 2814–2816.
Abstract: In this letter, the noise performance of NbN-based phonon-cooled hot electron bolometric quasioptical mixers is investigated in the 0.55–1.1 THz frequency range. The best results of the double-sideband <cd><2018>DSB<cd><2019> noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz, and 1250 K at 1.1 THz. The water vapor in the signal path causes significant contribution to the measured receiver noise temperature around 1.1 THz. The devices are made from 3-nm-thick NbN film on high-resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are typically 0.2Ï«2 um. The amount of local oscillator power absorbed in the bolometer is less than 100 nW.
|
