Point contact Josephson junctions operated as microwave mixers at 36 GHz show conversion gain and lower noise than cooled Schottky barrier diodes in the same application. The noise in such junctions with and without rf bias is explored both experimentally and theoretically. The noise power is found to be about a factor 2 above the thermal noise in the resistively shunted junction model. In contrast to previous reports, the inclusion of a shot noise term in the theory for no rf bias overestimates the observed noise substantially. (Author)Point contact Josephson junctions operated as microwave mixers at 36 GHz show conversion gain and lower noise than cooled Schottky barrier diodes in the same application. The noise in such junctions with and without rf bias is explored both experimentally and theoretically. The noise power is found to be about a factor 2 above the thermal noise in the resistively shunted junction model. In contrast to previous reports, the inclusion of a shot noise term in the theory for no rf bias overestimates the observed noise substantially. (Author)

STINAug 1, 19740 citations

Noise in Josephson mm-wave mixers

J. H. Claassen, Yuan Taur, P. L. Richards

Point contact Josephson junctions can function as millimeter wave heterodyne mixers with conversion gain. The best results achieved thus far show a single sideband conversion gain of 1.3 and a mixer contribution to the system noise temperature of 54 $sup 0$ K. Both of these results are approximately 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. The measured noise for a variety of junctions can be expressed as a universal function of the normalized rf frequency $Omega$ = h $omega$ /2eI/sub c/R. It is about a factor 2 larger than the calculated noise arising from the thermal noise in the junction shunt resistance, R. The noise calculation was done for the resistively shunted junction model using an analog junction simulator. (auth)Point contact Josephson junctions can function as millimeter wave heterodyne mixers with conversion gain. The best results achieved thus far show a single sideband conversion gain of 1.3 and a mixer contribution to the system noise temperature of 54$sup 0$K. Both of these results are approximately 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. The measured noise for a variety of junctions can be expressed as a universal function of the normalized rf frequency $Omega$ = h$omega$/2eI/sub c/R. It is about a factor 2 larger than the calculated noise arising from the thermal noise in the junction shunt resistance, R. The noise calculation was done for the resistively shunted junction model using an analog junction simulator. (auth)

Mar 1, 19750 citations

Noise in Josephson effect mm-wave mixers

J. H. Claassen, Y. Taur, P. L. Richards

We have recently shown that point contact Josephson junctions can function as millimeter wave heterodyne mixers with conversion gain. The best results achieved thus far show a single sideband conversion gain of 1.3 and a mixer contribution to the system noise temperature of 54K. Both of these results are ∼ 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. The measured noise for a variety of junctions can be expressed as a universal function of the normalized rf frequency\Omega = \hbar \omega/2eI_{c}R. It is about a factor 2 larger than the calculated noise arising from the thermal noise in the junction shunt resistance R. The noise calculation was done for the resistively shunted junction model using an analog junction simulator.We have recently shown that point contact Josephson junctions can function as millimeter wave heterodyne mixers with conversion gain. The best results achieved thus far show a single sideband conversion gain of 1.3 and a mixer contribution to the system noise temperature of 54K. Both of these results are ∼ 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. The measured noise for a variety of junctions can be expressed as a universal function of the normalized rf frequency\Omega = \hbar \omega/2eI_{c}R. It is about a factor 2 larger than the calculated noise arising from the thermal noise in the junction shunt resistance R. The noise calculation was done for the resistively shunted junction model using an analog junction simulator.

IEEE Transactions on MagneticsMar 1, 19751 citation

Noise in Josephson effect mm-wave mixers

J. H. Claassen, Y. Taur, P. L. Richards

We have recently shown that point contact Josephson junctions can function as millimeter wave heterodyne mixers with conversion gain. The best results achieved thus far show a single sideband conversion gain of 1.3 and a mixer contribution to the system noise temperature of 54K. Both of these results are ∼ 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. The measured noise for a variety of junctions can be expressed as a universal function of the normalized rf frequency \Omega = \hbar \omega/2eI_{c}R . It is about a factor 2 larger than the calculated noise arising from the thermal noise in the junction shunt resistance R. The noise calculation was done for the resistively shunted junction model using an analog junction simulator.We have recently shown that point contact Josephson junctions can function as millimeter wave heterodyne mixers with conversion gain. The best results achieved thus far show a single sideband conversion gain of 1.3 and a mixer contribution to the system noise temperature of 54K. Both of these results are ∼ 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. The measured noise for a variety of junctions can be expressed as a universal function of the normalized rf frequency \Omega = \hbar \omega/2eI_{c}R . It is about a factor 2 larger than the calculated noise arising from the thermal noise in the junction shunt resistance R. The noise calculation was done for the resistively shunted junction model using an analog junction simulator.

Sep 1, 19740 citations

Conversion gain and noise in a Josephson mixer

Y. Taur, J. H. Claassen, P. L. Richards

Fundamental mixing at 36 GHz in non-hysteretic Nb point contacts has been observed with overall conversion efficiencies in the range 0.33 ≤ η ≤ 4 and mixer noise temperatures in the neighborhood of TM ~ 200 K. The observed conversion efficiencies are in good agreement with the Resistively Shunted Junction model. The observed noise can be accounted for by assuming that the Johnson noise in the shunt resistor is the only source of noise driving the junction. Somewhat larger noise is seen from resonantly coupled mixers than is seen when the mixer is driven from an rf current source. Fundamental mixing in hysteretic junctions is limited to a narrow if bandwidth and gives much larger conversion gain but also larger noise. Parametric amplification at the if frequency is seen in hysteretic junctions. Fourth order harmonic mixing with ωLO/2 π at 9 GHz has been achieved with performance almost comparable to fundamental mixing. Cavity mode mixing appears less promising.Fundamental mixing at 36 GHz in non-hysteretic Nb point contacts has been observed with overall conversion efficiencies in the range 0.33 ≤ η ≤ 4 and mixer noise temperatures in the neighborhood of TM ~ 200 K. The observed conversion efficiencies are in good agreement with the Resistively Shunted Junction model. The observed noise can be accounted for by assuming that the Johnson noise in the shunt resistor is the only source of noise driving the junction. Somewhat larger noise is seen from resonantly coupled mixers than is seen when the mixer is driven from an rf current source. Fundamental mixing in hysteretic junctions is limited to a narrow if bandwidth and gives much larger conversion gain but also larger noise. Parametric amplification at the if frequency is seen in hysteretic junctions. Fourth order harmonic mixing with ωLO/2 π at 9 GHz has been achieved with performance almost comparable to fundamental mixing. Cavity mode mixing appears less promising.

Revue de Physique AppliquéeJan 1, 197439 citations

Point-contact Josephson mixers at 130 GHz

J. H. Claassen, P. L. Richards

The properties of point-contact Josephson junctions operated as mixers with an external local oscillator at 130 GHz have been studied, and the results compared with predictions of the resistively shunted junction model. It was found that the junction’s output noise could be within a factor of 1.5 of the model prediction based on the thermal-driving noise. When the coupling to the rf source was optimized, a factor of 2 discrepancy was typical. The measured conversion efficiency agreed with the model, within the experimental uncertainty in the equivalent microwave circuit. The best coupling was achieved in full-height waveguide. The best overall performance, measured using the hot/cold source technique, was a single sideband conversion efficiency of 0.30 and a mixer-noise temperature of 180 K (both ±20%). The best junctions were made of Nb, with carefully prepared points. Nonideal behavior in other junctions is ascribed to heating effects. There is some evidence that junctions whose resistance exceeds a threshold value of ∼60 Ω are no longer well described by the RSJ model. A discussion is given of possible improvements in performance with better junctions or improved rf matching.The properties of point-contact Josephson junctions operated as mixers with an external local oscillator at 130 GHz have been studied, and the results compared with predictions of the resistively shunted junction model. It was found that the junction’s output noise could be within a factor of 1.5 of the model prediction based on the thermal-driving noise. When the coupling to the rf source was optimized, a factor of 2 discrepancy was typical. The measured conversion efficiency agreed with the model, within the experimental uncertainty in the equivalent microwave circuit. The best coupling was achieved in full-height waveguide. The best overall performance, measured using the hot/cold source technique, was a single sideband conversion efficiency of 0.30 and a mixer-noise temperature of 180 K (both ±20%). The best junctions were made of Nb, with carefully prepared points. Nonideal behavior in other junctions is ascribed to heating effects. There is some evidence that junctions whose resistance exceeds a threshold value of ∼60 Ω are no longer well described by the RSJ model. A discussion is given of possible improvements in performance with better junctions or improved rf matching.

Journal of Applied PhysicsJul 1, 197828 citations

sup 0

K. Both of these results are approximately 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. The measured noise for a variety of junctions can be expressed as a universal function of the normalized rf frequency

Omega

= h

omega

/2eI/sub c/R. It is about a factor 2 larger than the calculated noise arising from the thermal noise in the junction shunt resistance, R. The noise calculation was done for the resistively shunted junction model using an analog junction simulator. (auth)