|
Loudkov, D., Tong, C. Y. E., Blundell, R., Kaurova, N., Grishina, E., Voronov, B., et al. (2005). An investigation of the performance of the superconducting HEB슠mixer as a function of its RF슠embedding impedance. IEEE Trans. Appl. Supercond., 15(2), 472–475.
|
Loudkov, D., Tong, C. - Y. E., Blundell, R., Kaurova, N., Grishina, E., Voronov, B., et al. (2005). An investigation of the performance of the superconducting HEB mixer as a function of its RF embedding impedance. IEEE Trans. Appl. Supercond., 15(2), 472–475.
Abstract: We have conducted an investigation of the optimal embedding impedance for a waveguide superconducting hot-electron bolometric (HEB) mixer. Three mixer chip designs for 800 GHz, offering nominal embedding resistances of 70 /spl Omega/, 35 /spl Omega/, and 15 /spl Omega/, have been developed. We used both High Frequency Structure Simulator (HFSS) software and scale model impedance measurements in the design process. We subsequently fabricated HEB mixers to these designs using 3-4 nm thick NbN thin film. Receiver noise temperature measurements and Fourier Transform Spectrometer (FTS) scans were performed to determine the optimal combination of embedding impedance and normal-state resistance for a 50 Ohm IF load impedance. A receiver noise temperature of 440 K was measured at a local oscillator frequency 850 GHz for a mixer with normal state resistance of 62 /spl Omega/ incorporated into a circuit offering a nominal embedding impedance of 70 /spl Omega/. We conclude from our data that, for low noise operation, the normal state resistance of the HEB mixer element should be close to the embedding impedance of the mixer mount.
|
Vachtomin, Y. B., Antipov, S. V., Maslennikov, S. N., Smirnov, K. V., Polyakov, S. L., Kaurova, N. S., et al. (2004). Noise temperature measurements of NbN phonon-cooled hot electron bolometer mixer at 2.5 and 3.8 THz. In Proc. 15th Int. Symp. Space Terahertz Technol. (pp. 236–241). Northampton, Massachusetts, USA.
Abstract: We present the results of noise temperature measurements of NbN phonon-cooled HEB mixers based on a 3.5 nm NbN film deposited on a high-resistivity Si substrate with a 200 nm – thick MgO buffer layer. The mixer element was integrated with a log-periodic spiral antenna. The noise temperature measurements were performed at 2.5 THz and at 3.8 THz local oscillator frequencies for the 3 µm x 0.2 µm active area devices. The best uncorrected receiver noise temperatures found for these frequencies are 1300 K and 3100 K, respectively. A water vapour discharge laser was used as the LO source. We also present the results of direct detection contribution to the measured Y-factor and of a possible error of noise temperature calculation. This error was more than 8% for the mixer with in-plane dimensions of 2.4 x 0.16 µm 2 at the optimal noise temperature point. The use of a mesh filter enabled us to avoid the effect of direct detection and decrease optical losses by 0.5 dB. The paper is concluded by the investigation results of the mixer polarization response. It was shown that the polarization can differ from the circular one at 3.8 THz by more than 2 dB.
|
|
Maslennikov, S., Vachtomin, Y., Antipov, S., Smirnov, K., Kaurova, N., Grishina, E., et al. (2004). NbN HEB mixers for frequencies of 2.5 and 3.8 THz. In Proc. Tenth All-Russian sceintific conference of student-physicists and young sceintists (VNKSF-10). Moscow.
|
Antipov, S. V., Vachtomin, Y. B., Maslennikov, S. N., Smirnov, K. V., Kaurova, N. S., Grishina, E. V., et al. (2004). Noise performance of quasioptical ultrathin NbN hot electron bolometer mixer at 2.5 and 3.8 THz. In Proc. 5-th MSMW (Vol. 2, pp. 592–594). Kharkov, Ukraine.
Abstract: To put space-based and airborne heterodyne instruments into operation at frequencies above 1 THz the superconducting NbN hot-electron bolometer (HEB) will be incorporated into heterodyne receiver as a mixer. At frequencies above 1.3 THz the sensitivity of the NbN HEB mixers outperform the one of the Schottky diodes and SIS-mixers, and the receiver noise temperature of the NbN HEB mixers increase with frequency. In this paper we present the results of the noise temperature measurements within one batch of NbN HEB mixers based on 3.5 mn thick superconducting NbN film grown on Si substrate with MgO buffer layer at the LO frequencies 2.5 THz and 3.8 THz.
|
