Performance of a two-junction array SIS-mixer operating around 345GHz

The authors have made a detailed study of the gain and noise of a SIS (superconductor-insulator-superconductor) heterodyne receiver at 345 GHz. An array of two Nb-Al₂O₃-Nb SIS junctions in series are used as the mixing element. The array is operated in a waveguide mount with a backshort and an E-plane tuner. The best receiver noise temperature achieved is 140 K DSB (double sideband). The embedding impedances were determined by fitting theory to the measured pumped curves. High-quality fits were obtained, providing the first detailed test of the Tucker-theory at frequencies above 300 GHz. The impedances found by this method are in very good agreement with impedances measured in a scale model at 3.3 GHz. From these embedding impedances, the gain and noise of the mixer were calculated over a full bias range using the Tucker theory in the three-port low-IF approximation. The measured dependence of mixer gain and noise on bias voltage, pump power and embedding impedance is in good agreement with theory. However the absolute values show discrepancies that appear to be independent of the bias parameters of the mixer     

超导隧道结亚谐波混频器的研究

本文探讨了新型的超导隧道结亚谐波混频器。其混频作用是通过由超导体—隔离体—超导体(SIS)构成的隧道结完成。在性能上可同通常的Schottky二极管亚谐波混频器媲美,基于Tucker量子混频理论,对这种新型混频器进行了噪声和变频效率的分析研究。     

The effect of mixer mount loss on the performance of SIS receivers

Tucker's quantum theory of mixing (in the 3-port approximation) is employed with Eisenhart and Khan's equivalent circuit for a junction mounted in waveguide to predict the gain of an SIS mixer as a function of guide impedance, series inductance, junction capacitance, IF load impedance and backshort loos. The improvements which will result from optimisation of these parameters are quantified. It is shown that for optimum performance a backshort VSWR>100 is required, which is hard to realise at high frequencies     

A low noise 230 GHz heterodyne receiver employing 0.25-μm2 area Nb-AlOx-Nb tunnel junctions

The authors report recent results for a full-height rectangular waveguide mixer with an integrated IF matching network. Two 0.25 μm ² Nb-AlO_x-Nb superconducting-insulating-superconducting (SIS) tunnel junctions with a current density of ≈8500 A/cm² and ωRC of ≈2.5 at 230 GHz have been tested. One of these quasiparticle tunnel junctions is currently being used at the Caltech Submillimeter Observatory in Hawaii. Detailed measurement of the receiver noise have been made from 200-290 GHz for both junctions at 4.2 K. The lowest receiver noise temperatures were recorded at 239 GHz, measuring 48 K DSB at 4.2 K and 40 K DSB at 2.1 K. The 230-GHz receiver incorporates a one-octave-wide integrated low-pass filter and matching network which transforms the pumped IF junction impedance to 50 Ω over a wide range of impedances     

An experimental study of harmonic SIS mixing at 205-235 GHz

A 230-GHz subharmonically pumped waveguide mixer employing superconducting tunnel junctions has been developed. We present, in this paper, an experimental study of harmonic superconductor-insulator-superconductor (SIS) mixing at 230 GHz, focusing mainly on its noise behavior. The mixer has a double-tuned waveguide structure and employs an array of four 1.7-/spl mu/m/sup 2/ Nb-AlOx-Nb SIS junctions in series, with /spl omega/R/sub n/C/sub j//spl sim/3 at 230 GHz. Harmonic quantum mixing occurred over an experimental frequency range of 205-235 GHz (local oscillator: 112.5-117.5 GHz), exhibiting corresponding double sideband noise temperatures of lower than 150 K, with a lowest value of 75 K at /spl sim/230 GHz. The measured mixer noise is believed to be the lowest yet reported for a mixer using subharmonic-pump configuration at this frequency. A phenomenon that we attribute to the third harmonic SIS mixing has also been observed.     

SIS quasiparticle mixers with bow-tie antennas

We have designed and evaluated planar lithographed W-band SIS mixers with bow-tie antennas and several different RF cou;ling structures. Both Pb-In-Au/Pb-Bi and Nb/Pb-In-Au junctions were used, each with ωR_NC«1. Single junctions and series arrays of five junctions directly attached to bow-tie antennas with no additional coupling structure gave poor performance, as expected. Single junctions with inductive microstrips and five-junction arrays with parallel wire inductors gave good coupling over bandwidths of ～5 and 25 percent respectively. Good agreement was found between design calculations based on a simple equivalent circuit and measurements of the frequency dependence of the mixer gain. When good coupling was achieved, typical values of mixer gain G_M (DSB)?0 dB, noise T_M(DSB)?150 K, and receiver noise ～200 K were observed. These measurements are referred to the cryostat window. When corrected for the estimated loss between the cryostat window and the antenna terminals, these values of gain are comparable to those observed for W-band waveguide mixers with IF matching, but the noise is significantly higher. There is evidence that ～100 K radiation surrounding the mixer reduces the gain and increases the noise. No systematic difference was observed between the performance of Pb-In-Au/Pb-Bi junctions and Nb/Pb-In-Au junctions when the area of the latter was made three times smaller and the current density three times larger so as to maintain the same capacitance and resistance.     

SIS Mixer to HEMT Amplifier Optimum Coupling Network (Short Paper)

The coupling network between a superconductor-insulator-superconductor (SIS) mixer and a high-electron-mobility-transistor (HEMT) amplifier is investigated from the point of view of minimizing the overall noise temperature and also increasing the saturation level of the mixer. The effect of a negative output impedance of the mixer upon the amplifier noise is considered and an optimum negative source resistance is found. The amplifier noise at this optimum negative source resistance is shown to be related to the noise wave coming out of the amplifier input terminals. Key words: SIS, HEMT, low-noise, negative resistance.     

Low noise SIS mixer for 230 GHz receivers of plateau de bure interferometer

We present a SIS mixer developed for 200 – 250 GHz band receivers of Plateau de Bure Interferometer. We demonstrate the minimum DSB receiver noise of 20 K at 220 GHz. The average receiver noise of 25 K is possible in 200 – 250 GHz range. The receiver conversion gain and output noise instability of 10^?4 on the time scale of 1 minute is comparable with the Shottky receivers performance. The minimum measured SIS mixer noise of about 10 K is close to the quantum limit. The waveguide SIS mixer with a single backshort has two junction array with inductively tuned junctions. The Nb/Al Oxide/Nb SIS junctions are 2.24 µm² each with the Josephson critical current density of 3.2 KA/cm². The thermal properties of the SIS mixer are studied. The mixer band of the low noise operation is in a good agreement with the design requirements.     

Characterization of the IF Noise of a Submillimeter SIS Receiver

A fitting method is presented here for the accurate characterization of the IF noise contribution of a sub-millimeter SIS receiver. By fitting the mixer's IF output power response and junction's IV curve of an SIS mixer without LO pumping, we can obtain the IF noise contribution, the physical temperature of the isolator connected just behind the SIS mixer, the output mismatching of the mixer, and the total gain of the IF chain. Differing from a conventional method, which only uses the normal-state (linear) branch of the junction's IV curve, the method proposed here also includes the nonlinear portion around the gap voltage. The dynamic resistance in this portion is varied dramatically, providing us a good probe to characterize the output mismatching of the mixer, as well as other parameters.     

Submillimeter-wave detection with superconducting tunnel diodes

The review presents a theoretical framework for understanding submillimeter detection using an optical photodiode theory. Both gain and noise in the superconductor-insulator-superconductor (SIS) mixer are described in terms of mixing on a photodiode. The role of impedance matching in the proper design of an SIS mixer is described. A variety of methods for achieving good impedance match at submillimeter frequencies are presented. The state of the submillimeter SIS mixer art as practiced in a variety of laboratories is described and summarized     

One Aspect of Minimum Noise Figure Microwave Mixer Design

A theory is derived which enables a direct measurement of the optimum RF impedance for minimum noise figure. This is achieved by an extension of Pound's method for loss measurements. Also, an analysis is made of the relation between minimum noise figure and maximum gain of the mixer represented as a two-port network. The procedure consists of first matching the RF signal input terminals with short-circuited IF terminals. Next open-circuited IF terminal conditions are obtained by a circuit used by Pound. Then a reference plane is determined coinciding by preference with the plane of a maximum in the standing wave pattern of VSWR = r. A discontinuity is finally introduced that would have a VSWR of p = /spl radic/r and have its maximum or minimum at the plane of reference.     

Simulated performance and model measurements of an SIS waveguide mixer using integrated tuning structures

A three-port approximation of the quantum mixer theory is employed to perform mixer gain calculations at 230 GHz for SIS junctions with integrated tuning structures. In addition, the embedding impedance range of a waveguide mixer mount has been obtained from model measurements and has been included in the gain calculations. The results show that even moderately small junctions can perform well in a waveguide environment when an integrated tuning structure is used. A three-element tuning circuit is presented that would allow broad band operation with a fixed embedding impedance which is important for applications using a planar antenna structure.     

Quasi-optical slot antenna SIS mixers

A quasi-optical SIS mixer designed for efficient radiation coupling is described. The mixer uses a twin-slot antenna which has the advantages of a good beam pattern and a low impedance. The radiation and impedance characteristics of the antenna were obtained from a moment-matched calculation. Tapered superconducting microstrip transmission lines are used to carry the radiation from the slot antennas to the tunnel junction. The effective impedance seen by the tunnel junction is quite low, about 4 Ω, which allows micron-size junctions to be used at 500 GHz. The mixers have been fabricated using Nb/Al-oxide/Nb tunnel junctions and a receiver noise temperature of 420 K (DSB) was measured at 490 GHz, which is the best yet obtained for a quasi-optical mixer at this frequency. The comparatively large junction area increases the mixer saturation power and allows strong suppression of noise from the Josephson effect by the application of a magnetic field of modest strength     

Tunerless mixer mount for an SIS 80–120 GHz receiver

We have developed a 100 GHz band SIS receiver using a simple mixer mount design, which does not use variable RF tuning elements, such as a back short tuner or an E-plane tuner. The mixer mount structure was designed using calculations of the embedding impedance of the mixer mount, and of receiver performance, using the quantum theory of mixing under the 3-port approximation. The mixer mount structure we designed has a 1/7 reduced height waveguide and a “back short cavity”. We have constructed a receiver system using this tunerless mixer mount design, and we have measured the receiver noise temperatures for two different tunerless mixer mounts using arrays of four Nb/Al-AlOx/Nb junctions. For one of the two mixer mounts, we obtained very low noise receiver temperatures, 35–70 K, over the very wide frequency range of 80–120 GHz. We also show that, due to IF missmatching, the noise of the IF amplifier is the main contributor to the receiver noise temperature. We also compared the results of measurements with the results of our theoretical calculations. Our calculations reproduced the tendency of receiver performances very well. This tunerless mixer mount has application on the MM-Wave Array and in the multi-beam receiver.     

Notes on a Crystal Mixer Performance

A simple relation between optimum rf source impedance for minimum noise figure and the nominal conversion loss of a mixer is derived. This impedance is related to the input mismatch and its dependence on the type of IF amplifier input circuit is discussed. Relations between the crystal noise temperature and mixer noise temperature as a function of conversion loss are derived for different load conditions at the image frequency terminals.     

A 40 GHz band SIS receiver using Nb/Al−AlOx/Nb array junctions

A 40 GHz band SIS mixer receiver has been built using Nb/Al?AlOx/Nb array junctions and a 4.3 K closed cycle helium refrigerator. The minimum conversion loss of the mixer is 2±1 dB and the single sideband receiver noise temperature (T_RX (SSB)) is as low as 110±10 K at 36 GHz. T_RX (SSB) is almost constant in the IF bandwidth of 600 MHz. The mixer saturation level is as high as 15 nW, which is comparable to the injected LO power.     

A dual-polarized quasi-optical SIS mixer at 550 GHz

In this paper, we describe the design, fabrication, and the performance of a low-noise dual-polarized quasi-optical superconductor-insulator-superconductor (SIS) mixer at 550 GHz. The mixer utilizes a novel cross-slot antenna on a hyperhemispherical substrate lens, two junction tuning circuits, niobium trilayer junctions, and an IF circuit containing a lumped element 180° hybrid. The antenna consists of an orthogonal pair of twin-slot antennas, and has four feed points, two for each polarization. Each feed point is coupled to a two-junction SIS mixer. The 180° IF hybrid is implemented using a lumped element/microstrip circuit located inside the mixer block. Fourier transform spectrometer measurements of the mixer frequency response show good agreement with computer simulations. The measured co-polarized and cross-polarized patterns for both polarizations also agree with the theoretical predictions. The noise performance of the dual-polarized mixer is excellent giving uncorrected receiver noise temperature of better than 115 K (double sideband) at 528 GHz for both the polarizations     

Low noise completely quasioptical SIS receiver for radioastronomy at 115 GHZ

Completely quasioptical heterodyne SIS receiver for radioastronomical applications at 115 GHz was designed and tested. Gaussian beam two lens input guide system and open structure SIS mixer with immersion lens were used. Integrated quasioptical structure consists of planar equiangular spiral antenna and superconductor—insulator—superconductor (SIS) tunnel junction as a mixing element connected to the antenna via microstrip impedance transformer. The best SIS mixer noise temperature at hot input and for heterodyne frequency 109.8 GHz with IF central frequency 1.4 GHz (DSB) was 28±7 K at the first quasiparticle step and 8±6 K at the second step.     

A sideband separating mixer for 85-115 GHz

This paper presents the results of development and tests of a sideband separating heterodyne receiver for the 85-115 GHz band with superconducting tunnel junctions (SIS) as frequency down converters. Sideband separation is achieved by using a quadrature scheme where two identical mixer junctions are pumped by a local oscillator (LO) with 90/spl deg/ phase difference. We used an innovative mixer layout where the quadrature scheme is implemented using waveguide-based and integrated on-chip components. We employed an additional pair of SIS junctions as terminations for LO-injection directional couplers.     

Analysis of SIS heterojunctions for use as mm-wave mixers exhibiting coversion gain

We apply the quantum formulation of heterodyne mixer theory to SIS heterojunctions (junctions between dissimilar superconductors). Conversion gain is predicted over a wide range of mm-wave frequencies in the 3-port Y-mixer model by exploiting the naturally occurring region of negative conductance in the DC I-V characteristic. In the signal frequency range 50–250 GHz this region persists in the pumpedjunction I–V characteristic for local oscillator power <1 nW and leads to a negative conductance at the mixer's IF port.