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Noise and Conversion Efficiency of High-T c Superconductor Josephson Mixers

Oliver Harnack, S. Beuven, Marian Darula, H. Kohlstedt, Michael A. Tarasov, Е. А. Степанцов, Z. G. Ivanov

Published Mar 1, 1998• 1 citation
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Abstract

We report on experimental studies of the noise performance and conversion efficiency of high-Te Josephson mixers at frequencies between 90 GHz and 550 GHz. The heterodyne mixing experiments have been performed by using YBa2Cu307_8 step-edge junctions and bicrystal junctions on MgO (E--9.6) substrates. We studied the Josephson mixer performance for the case of internal pumping (selfpumping) and external pumping. Receiver noise measurements in a waveg,uide setup for the case of external pumping at 90-94 GHz gave formally calculated double-side-band (DSB) mixer noise temperatures (Tm) of about 2000 K at physical temperatures of 10 K. Similar measurements in a quasioptical setup at 4.2 K and at operation frequencies of 430 GHz and 546 GHz yielded mixer noise temperatures of 1200 K and 1100 K, respectively. Using the internal pumped mode, i.e. mixing without external local oscillator signal, we also obtained clear IF response in hot/cold-measurements. The formally calculated Tm were between 580 K and 2300 K.

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We have measured the noise performance and conversion efficiency of Y–Ba–Cu–O bicrystal Josephson mixers at operating temperatures between 20 and 60 K and at operating frequencies around 90 GHz. A double-sideband mixer noise temperature of about 1600 K and a conversion efficiency of −10 dB at 20 K operating temperature has been measured using the Y-factor method. The absorbed local oscillator power was in the range of 10 nW. The dependence of the mixer performance on the normalized frequency Ω and the fluctuation parameter Γ has been studied. In accordance with the resistively shunted junction model, the experimental data show the presence of excess noise. The temperature dependence of the mixer noise temperature can be explained by the variation of the linewidth of the Josephson oscillations with the operating temperature.

Applied Physics Letters•Mar 27, 2000•12 citations
We report on experimental studies of the noise performance and conversion efficiency of high-Te Josephson mixers at frequencies between 90 GHz and 550 GHz. The heterodyne mixing experiments have been performed by using YBa2Cu307_8 step-edge junctions and bicrystal junctions on MgO (E--9.6) substrates. We studied the Josephson mixer performance for the case of internal pumping (selfpumping) and external pumping. Receiver noise measurements in a waveg,uide setup for the case of external pumping at 90-94 GHz gave formally calculated double-side-band (DSB) mixer noise temperatures (Tm) of about 2000 K at physical temperatures of 10 K. Similar measurements in a quasioptical setup at 4.2 K and at operation frequencies of 430 GHz and 546 GHz yielded mixer noise temperatures of 1200 K and 1100 K, respectively. Using the internal pumped mode, i.e. mixing without external local oscillator signal, we also obtained clear IF response in hot/cold-measurements. The formally calculated Tm were between 580 K and 2300 K.
The authors report on the mixing properties of high-temperature superconductor bicrystal Josephson junctions at 345 GHz and high-operating temperatures. A variable backshort and E-plane tuner enabled the control of impedance matching between the junction and the RF environment. The local oscillator frequency and intermediate frequency were 345 and 1.4 GHz, respectively. The double-side band (DSB) mixer noise temperature and the conversion efficiency were determined using the hot/cold method. The authors observed that the noise temperature was strongly dependent on the matching conditions. The lowest noise temperatures were observed for tuner positions supporting the formation of a subharmonic step which appeared between the zeroth and first Shapiro step. At T = 20 K they obtained a lowest DSB mixer noise temperature of 1003 K and a conversion efficiency of -1.2 dB. They have investigated the dependence of the noise temperature on the operating temperature in detail. The impact of resonances on the device performance will be discussed.
We report on our experimental studies of noise properties and conversion efficiency of high-T/sub c/ Josephson mixers and high-T/sub c/ hot-electron bolometric (HEB) effect mixers at frequencies between 90 GHz and 550 GHz. Noise measurements using a Josephson mixer at 90 GHz gave noise temperatures of 2900 K at 20 K. Measurements in a quasi-optical setup at 430 GHz and 546 GHz showed mixer noise temperatures of 1200 K and 1100 K at 4.2 K, respectively. Heterodyne mixing experiments using high-T/sub c/ HEB mixers have been performed at temperatures around 78 K and at frequencies between 78 GHz and 119 GHz. The uncorrected conversion efficiency at an intermediate frequency of 3 GHz was measured to be -30 dB.
A Josephson quasioptical detector comprising YBaCuO junction on bicrystal MgO substrate, integrated log-periodic Au antenna, MgO extended hyperhemisphere lens attached to the substrate and 1.4 GHz cold amplifier with cold circulator has been designed, fabricated and experimentally studied. We fabricated several integrated Josephson junctions 1-2 /spl mu/m wide which at 4.2 K demonstrate RSJ IV curves with critical currents 100-300 /spl mu/A and normal resistance of 10-20 /spl Omega/. The noise temperature (T/sub N/) at 4.2 K and 330 GHz measured by a hot/cold load method in fundamental mixing mode with external BWO local oscillator brings T/sub N/=1100 K for the junction shunted by low-inductance resistive shunt and T/sub N/=1400 K without shunting. At bath temperatures of 20-40 K the noise temperature was in the range 1500-3000 K, at 50 K the noise temperature was below 2000 K, and at 60-70 K increased over 3000 K in the frequency range 310-586 GHz. The noise temperatures measured in the self-pumping mode vary between 580-2300 K with dc bias in the range 0.1-0.5 mV. The linewidth of Josephson oscillations has been extracted from a selective detector response and IF noise voltage dependence. The measured excess noise can be attributed to shot noise and multiple Andreev reflection in pinholes with Ss'S structure. We observed small subharmonic steps in IV curve and noise dependencies, which are typical for SNS junctions.
We report on the mixing properties of high-T, superconductor (HTS) Josephson junctions. Direct radiation and heterodyne mixing experiments in the frequency range 78 GHz-119 GHz have been performed using YBa 2Cu30 7_ x (YBCO) step-edge junctions (SEJ) and bicrystal junctions (BO) on LaA10 3 and MgO substrates. Under external radiation our junctions showed harmonic phase synchronization (Shapiro steps) up to 1.88 THz. Junctions with current voltage characteristics (PVC) dose to predictions of the resistively shunted junction model (RSJ) were mounted into a heterodyne mixing setup. Under the radiation of two monochromatic signals we obtained conversion efficiencies around -14 dB in the 11 GHz intermediate frequency (IF) band. In the fundamental mixing regime we observed response at IF at working temperatures up to 72K. We demonstrated the operation of HTS Josephson junctions in the self-mixing mode. The experimental results are in good agreement with simulations using the RSJ model.
A waveguide mixer based on a Josephson junction made from a high-temperature superconductor (HTS) has been analysed at frequencies of 90 GHz and 115 GHz. The mixer consisted of a single-grain-boundary bicrystal junction which was integrated with a bow-tie antenna and a microstrip filter structure fabricated on an MgO substrate. Two different designs of mixer block were tested. Using the first design the best noise performance was measured at a local oscillator (LO) frequency of about 90 GHz. At the projected LO frequency of 115 GHz significant deterioration of performance was observed. A computer simulation of the mixer chip and substrate channel structure was performed using the 3D simulation program HFSS. Sufficient RF signal rejection by the filter structure was confirmed at 90 GHz. After a simulation cycle at 115 GHz the substrate channel in the mixer block was modified. Using this second design we measured a double-sideband mixer noise temperature of 1090 K at 10 K operating temperature which is the best performance of an HTS Josephson mixer to date obtained at this frequency and temperature.
We have measured the noise performance and conversion efficiency of Y–Ba–Cu–O bicrystal Josephson mixers at operating temperatures between 20 and 60 K and at operating frequencies around 90 GHz. A double-sideband mixer noise temperature of about 1600 K and a conversion efficiency of −10 dB at 20 K operating temperature has been measured using the Y-factor method. The absorbed local oscillator power was in the range of 10 nW. The dependence of the mixer performance on the normalized frequency Ω and the fluctuation parameter Γ has been studied. In accordance with the resistively shunted junction model, the experimental data show the presence of excess noise. The temperature dependence of the mixer noise temperature can be explained by the variation of the linewidth of the Josephson oscillations with the operating temperature.