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.     

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。     

A 275–370 GHz Receiver Employing Novel Probe Structure

We present the results of the development of a 275–370 GHz, fixed-tuned double sideband (DSB) receiver based on superconductor-insulator-superconductor (SIS) junction mixer. The mixer block uses a full height rectangular waveguide and employs a novel radial-like probe structure with integrated bias-T. The measured uncorrected receiver noise temperature is 30–50 K corresponding to about 2–3 quantum noise across the full frequency band with an IF from 3.8 to 7.6 GHz. The mixer is to be used on the Atacama Pathfinder EXperiment (APEX) submillimeter telescope in Chile.     

Quantum noise in heterodyne detection

A fully quantum mechanical theory of diode mixers which includes quantization of the external circuit is presented. We find that Tucker's theory for SIS mixer conversion efficiencies is correct, but that his expression for the measurement noise must be augmented by an amount corresponding to half a photon at every frequency to which the mixer responds. Noise in high quality SIS mixers is shown to be accurately described by the conceptually simpler photodiode mixer noise theory. The radiation coupling efficiency term, η, which appears in photodiode theory turns out to be the coupling efficiency between the signal source admittance and the admittance which the SIS presents to the LO. Our theory reduces to Caves' quantum linear amplifier formalism, and therefore predicts measurement noises bounded by the quantum lower limit ofhv/k_{B}. Predictions of performance versus frequency for SIS's are made. We predict that NbN SIS's will behave as nearly ideal photodiodes for frequencies as high as 3000 GHz.     

A 100-GHz fixed-tuned waveguide SIS mixer exhibiting broadbandwidth and very low noise temperature

This paper presents design and performance data for a 100-GHz waveguide superconductor-insulator-superconductor (SIS) mixer, which is incorporated with a twin-junction device (i.e., two identical junctions connected in parallel through a tuning inductance) and a fixed-tuned broad-band waveguide mixer mount. The 100-GHz mixer is actually developed as a prototype of the 500-GHz one. The constructed 100-GHz SIS receiver results in an overall receiver noise temperature (DSB) of less than 40 K over the frequency range from 80-120 GHz, with a minimum value of just 20 K that is four times as large as the quantum limit (i.e., 4ℏω/k). Such a performance is comparable or even superior to those of the best mechanically tunable waveguide SIS receivers at the same frequency band. In addition, some interesting mixing behaviors related to this two-junction device are described in detail     

Determination of the spectral response of sis-junctions by a direct detection measurement

We present a simple method to determine the spectral response of an SIS detector in the millimeter and submillimeter wavelength range from its current response to a chopped cold-load. This direct detection response is also a good indicator of quantum efficiency and mixer noise temperature when using the SIS junction in heterodyne mode. A simple experimental setup without local oscillator, cryogenic IF-amplifier or any quasioptical interferometer allows a quick diagnosis of integrated planar impedance matching structures.     

A Fixed-Tuned W-Band Waveguide SIS Mixer with 4.0-7.5 GHz IF

The design and performance of a fixed-tuned W-band SIS mixer with a wide band IF of 4.0-7.5 GHz is presented. Waveguide-to-stripline transition of the SIS mixer is designed using the lumped-gap-source port provided by HFSS^TM. Measured receiver noise temperature is less than 25 K in the frequency range of 95-120 GHz, with a minimum value of around 19 K achieved. Mixer noise temperature is determined to be about 8.5 K, which is around twice the quantum limit (i.e., 2hw/k). In spite of the high IF frequencies (f ₀ = 6 GHz), the performance of the SIS receiver is comparable or even superior to those of the best mechanically-tunable waveguide SIS receivers at low IF frequencies (f ₀ = 1.5 GHz). This result suggests that it is easy to design waveguide-to-stripline transitions without scale-model measurements.     

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.     

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.     

A Low-Noise 230 GHz SIS Receiver for Radio Astronomy Employing Untuned Nb/AlOx/Nb Tunnel Junctions

A heterodyne receiver based on a ～1/3 reduced height rectangular waveguide SIS mixer with two mechanical tuners has been built for astronomical observations of molecular transitions in the 230 GHz frequency band. The mixer used an untuned array (ωR_nC_j≈3, R_n≈70 Ω) of four Nb/AIOx/Nb tunnel junctions in series as a nonlinear mixing element. A reasonable balance between the input and output coupling efficiencies has been obtained by choosing the junction number N=4. The receiver exhibits DSB (Double Side Band) noise temperature around 50 K over a frequency range of more than 10 GHz centered at 230 GHz. The lowest system noise temperature of 38 K has been recorded at 232.5 GHz. Mainly by adjusting the subwaveguide backshort, the SSB (Single Side Band) operation with image rejection of ≥ 15 dB is obtained with the noise temperature as low as 50 K. In addition, the noise contribution from each receiver component has been studied further. The minimum SIS mixer noise temperature is estimated as 15 K, pretty close to the quantum limit ?v/k～11 K at 230 GHz. It is believed that the receiver noise temperatures presented are the lowest yet reported for a 230 GHz receiver using untuned junctions.     

A 400–500 GHz Balanced SIS Mixer with a Waveguide Quadrature Hybrid Coupler

We have developed a 400–500 GHz low-noise balanced SIS (Superconductor Insulator Superconductor) mixer, which is based on a waveguide RF quadrature hybrid coupler. The RF quadrature hybrid was designed and fabricated as a broadband hybrid with good performance at 4 K. The fabricated RF quadrature hybrid was measured at room temperature with a submillimeter vector network analyzer to check amplitude and phase imbalance between two output ports. Then the balanced mixer was assembled with the RF hybrid, two DSB mixers, and a 180° IF hybrid. Several important parameters such as noise temperature, LO power reduction, and IF spectra were measured. The LO power reduction is defined as how much LO power the balanced mixer saves compared with a typical single-ended mixer. The measured noise temperature of the balanced mixer was ~ 55 K at the band center which corresponds to ~ 3 times the quantum noise limit (hf/k) in DSB, and ~ 120 K at the band edges. The noise performance over LO frequency was almost the same as that of the worse DSB mixer used in the balanced mixer. In addition the LO power required for the balanced mixer is ~ 11 dB less than that of the single-ended mixers.     

A planar quasi-optical SIS receiver

A planar, quasi-optical SIS (superconductor-insulator-superconductor) receiver operating at 230 GHz is described. The receiver consists of a 2×5 array of half-wave dipole antennas with niobium-aluminum oxide-niobium SIS junctions on a quartz dielectric-filled parabola. The 1.4-GHz intermediate frequency is coupled from the mixer via coplanar strip transmission lines and 4:1 balun transformers. The receiver is operated at 4.2 K in a liquid helium immersion cryostat. Accurate measurements of the performance of single untuned array receiver elements are reported. A mixer noise temperature of 89 K DSB (double sideband), receiver noise temperature of 156 K DSB and conversion loss of 8 dB into a matched load have been obtained. This mixer noise temperature is approximately a factor of two larger than that of current state of the art waveguide mixers using untuned single junctions a the same frequency     

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.     

180–425 GHz low noise SIS waveguide receivers employing tuned Nb/AIO x /Nb tunnel junctions

We report recent results on a 20% reduced height 270–425 GHz SIS waveguide receiver employing a 0.49 µm² Nb/AlO _x /Nb tunnel junction. A 50% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner reduced height waveguide mixer block. The junction uses an “end-loaded” tuning stub with two quarter-wave transformer sections. We demonstrate that the receiver can be tuned to give 0–2 dB of conversion gain and 50–80% quantum efficiency over parts of it's operating range. The measured instantaneous bandwidth of the receiver is ≈ 25 GHz which ensures virtually perfect double sideband mixer response. Best noise temperatures are typically obtained with a mixer conversion loss of 0.5 to 1.5 dB giving uncorrected receiver and mixer noise temperatures of 50K and 42K respectively at 300 and 400 GHz. The measured double sideband receiver noise temperature is less than 100K from 270 GHz to 425 GHz with a best value of 48K at 376 GHz, within a factor of five of the quantum limit. The 270–425 GHz receiver has a full 1 GHz IF passband and has been successfully installed at the Caltech Submillimeter Observatory in Hawaii. Preliminary tests of a similar junction design in a full height 230 GHz mixer block indicate large conversion gain and receiver noise temperatures below 50K DSB from 200–300 GHz. Best operation is again achieved with the mixer tuned for 0.5–1.5 dB conversion loss which at 258 GHz resulted in receiver and mixer noise temperature of 34K and 27K respectively.     

An 85-116 GHz SIS receiver using inductively shunted edge junctions

A superconductor-insulator-superconductor (SIS) mixer with a broadband integrated tuning structure is described. The mixer is tunable from 85 to 116 GHz and at 114 GHz has a noise temperature ⩽5.6 K double sideband (DSB) and unity DSB conversion gain. The mixer noise temperature is less than or comparable to the photon noise temperature hf/k≈5.5 K. Referred to the mixer input flange, the receiver noise temperature is ⩽9.5 K DSB when operated with an L -band HEMT (high-electron-mobility transistor) IF amplifier. Saturation measurements have been made using CW and broadband noise sources     

Noise parameters of SIS mixers

It has been shown that low-noise receivers can be constructed at millimeter wavelengths by using mixers containing superconducting tunnel junctions as the nonlinear elements. This is possible because of both the low intrinsic noise of these devices and their potential for high conversion gain. Here, the quantum theory of mixing is used to derive the full-noise parameters and small-signal parameters of sinusoidally pumped SIS (superconductor-insulator-superconductor) junctions. These are then put into a form that allows the theory of two-port linear networks to be brought to bear, allowing calculation of such useful parameters as minimum noise temperature, optimum source impedance, available (or exchangeable) gain at minimum noise, and stability factor. These quantities are properties of the pumped junction that do not depend on the source or load impedance, but do depend on the terminations at the image and harmonic sideband frequencies. The harmonic sidebands are taken to be shorted, and the image termination dependence is studied. Numerical results are presented for both ideal (BSC theory) and practical (measured current-voltage characteristic) junctions. The noise parameters of the cascade connection of an SIS mixer and a (noisy) IF amplifier are considered, leading to a specification of the optimum coupling network between the two. It is noted that the SIS mixer is usually not unconditionally stable, but that oscillation can be avoided by careful design of the IF coupling network     

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.     

A 350GHz Radial-Probe SIS Mixer for Astronomical Imaging Arrays

We have developed a 330-370GHz SIS mixer for small-format, heterodyne, astronomical imaging arrays. Fixed-tuned broadband operation is achieved by means of a superconducting radial waveguide probe. A horn-reflector antenna provides high-efficiency optical coupling. Using a variable-temperature cryogenic noise source, we measured a DSB system noise temperature of 32±1K. The mixer contributes 3±3K, supporting the theoretically-predicted result that the noise temperature of a DSB mixer can be less than hω/2κ (8.6K)     

Low noise submillimeter SIS receiver with niobium nitride quasiparticle tunnel junctions

We have developed and tested a submillimeter waveguide SIS mixer with NbN-MgO-NbN quasiparticle tunnel junctions. The two junction array is integrated in a full NbN printed circuit. The NbN film critical temperature is 15 K and the junction gap voltage is 5 mV. The size of the junctions is 1.4 × 1.4 µm and Josephson critical current density is about 1.5 KA/cm² resulting in junction R_NωC product about 40. The inductive tuning circuit in NbN is integrated with each junction in two junction array. A single non contacting backshort was tuned at each frequency in the mixer block. At 306 GHz the minimum DSB receiver noise temperature is as low as 230 K. The sources of the receiver noise and of the limits of the NbN SIS submillimeter mixer improvement are discussed.     

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