Low noise single-ended mixer for 230 GHz

Performance of a single-ended fundamental frequency diode mixer, designed for cooled operation in the frequency range 190?260 GHz, is reported. At 230 GHz the best single sideband (SSB) mixer temperature obtained was 300 K, when the mixer was cooled to 20 K, with a corresponding SSB conversion loss of 5.9 dB. The significant improvement compared to previously reported results is attributed to the novel mixer mount design and to the optimum empirical choice of diode electrical parameters.     

Understanding noise in SIS receivers

A simple laboratory test receiver has been built and used to examine some interesting aspects of heterodyne mixing with superconductor-insulator-superconductor tunnel junctions. Experiments made over the frequency range 220 GHz–490 GHz using junctions of both the Pb/Bi/In-type and the Pb/In/Au-type indicate that, in the majority of cases, a receiver may be characterized through a few simple measurements made external to it's dewar. We also show that, at high local oscillator drive levels, excess mixer noise may be generated which may be removed by the application of a magnetic field. This is of particular relevance to high frequency mixing where Josephson interference may be strong. Finally, it is observed that even in the presence of severe interference a stable bias point, free from excess mixer noise, is often possible.     

Low-noise SIS heterodyne receiver at 230 GHz

A 230 GHz laboratory receiver has been built using a superconductor-insulator-superconductor (SIS) junction as the mixing element. The junction is mounted in 4:1 reduced-height waveguide, terminated at one end with a circular adjustable backshort. Recent results indicate a receiver noise temperature of TR ? 120 K (DSB).     

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     

A quasiparticle SIN mixer for the 230 GHz frequency range

We report on quasiparticle mixing in the frequency range 220 to 230 GHz using SIN junctions. The lowest double sideband receiver noise temperature measured was about 230 K. This result shows that the SIN junction provides an interesting alternative for high frequency heterodyne receivers where pair tunneling in SIS junctions could give rise to interference from Josephson effects.     

Low noise broadband tunerless waveguide sis receivers for 440–500 GHz and 630–690 GHz

We have developed broadband SIS heterodyne receivers for the frequency ranges from 440 to 500 GHz and 630 to 690 GHz. The mixerblocks contain a punched waveguide cavity which forms a fixed backshort. The substrate channel is sawed across the waveguide. The horn antenna is flanged to the mixerblock. The blocks are easy and quickly to manufacture even for the small dimensions needed in the submm wavelength range. We use Nb-Al₂O₃-Nb junctions with areas of 0.8 µm² and integrated three step niobium tuning structures. With this design we achieve instantaneous double sideband receiver noise temperatures around 120 K over the frequency range from 660 to 690 GHz and around 80 K from 440 to 500 GHz. The mixer performance agrees well with the design calculations for the tuning structures.     

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.     

Characterization of a 680–760 GHz SIS waveguide mixer

A heterodyne waveguide receiver employing 1 µm² Nb superconducting tunnel junctions with on chip integrated tuning structures is characterized from 680–760 GHz. Several different types of integrated tuning structures are investigated. Lowest DSB receiver noise temperatures of 310 K at 709 GHz and 400 K at 720 GHz are measured. Analysis of the data shows that the loss of the superconducting tuning structures has a major influence on the overall receiver performance. A 25% reduction in receiver noise temperature is observed if the mixer is cooled from 4.2 K to 2 K, which we attribute to the reduced loss of the superconducting microstrip lines at lower temperatures. The calculated performance of the different tuning structures is shown to be in good agreement with the actual receiver noise measurements.     

Open structure log-periodic SIS receivers at 180 and 305 GHz

Two open structure heterodyne receivers have been designed and tested at 180 and 305 GHz. The RF signal is coupled via a seven teeth log-periodic planar antenna to the mixer. The beam efficiency of the antenna is 65 %. The coupling efficiency to the fundamental gaussian mode is higher than 90%. The mixer incorporates a series array of two SIS Nb-Al/AlO_x-Nb junctions. Photolithographical techniques have been employed to fabricate the antennas and the junctions. Double side band noise receiver temperatures of 95 K at 190 GHz and 160 K at 305 GHz have been measured.     

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     

Minimum noise temperature of a practical SIS quantum mixer

Noise temperature of a SIS quantum mixer has been calculated as function of local oscillator voltage and signal source conductance on the basis of a measured I–V characteristic. Applying Tucker's quantum theory of mixing /1/, it is shown that the SIS mixer is quantum noise limited. Using cryogenic intermediate frequency amplifier, receiver noise temperature of 20 K seems to be possible at mm wavelength.     

A low noise 230 GHz sis receiver

We report the construction of a 230GHz superconductor insulator superconductor (SIS) tunnel junction receiver utilizing a full height rectangular waveguide mixer with two tuning elements i.e. an E plane and backshort tuner. Preliminary results indicate that the receiver exhibits a best double side-band response of 114K±15K (averaged over a 500 MHz IF bandwidth) at a frequency of 228GHz and at an ambient temperature of approximately 2.4K. With the exception of a region in the vicinity of 250GHz, the receiver shows an excellent response over an RF input range of 200 to 290GHz. Finally, the receiver has been successfully employed on the new Caltech Submillimeter Observatory 10m antenna on Mauna Kea, Hawaii.     

An SIS mixer for 90–120 GHz with gain and wide bandwidth

An SIS mixer for the 3 mm wavelength band has been developed. It has sufficient RF bandwidth to allow double-sideband operation at an IE of 1.4 GHz. Available gain of around 3 dB has been measured, along with mixer temperatures of 20 to 40K (both double sideband). The junctions were fabricated using a lead-alloy technology (Pb?In?Au/oxide/-Pb?Bi). Coupling and tuning structures were integrated onto a quartz substrate along with the junctions. The measurements were made at physical temperatures around 3.1K, achieved with a closed-cycle refrigerator.     

100 GHz mixer vertically integrated (stacked) SIS junction array

A Vertically Integrated Array (stacked array) of single windowSIS junctions (VIA SIS), based on a stacked five layer structure of Nb-AlO_x-Nb-AlO_x-Nb, has been fabricated and tested in a quasi optical mixer configuration at 106 GHz. This particular VIA SIS design has two stacked junctions fabricated by standard tri-layer process employing photolithography, reactive ion and wet etching processes. A simple expression for calculating the specific capacitance of single and arrayed SIS junctions is suggested. Due to the absence of interconnection leads between the individual junctions and reduced overall capacitance, compared to a single SIS junction, has the VIA SIS good future prospects for use in submillimeter wave SIS mixers The VIA SIS may be regarded as a lumped rather than a distributed structure at least up to the gap frequency at 730 GHz for Nb. DC-IV measurements show high quality of the Individual SIS junctions and good reproducibility of the array parameters over the substrate area. The first VIA SIS mixer experiments yielded a receiver noise temperature of 95 K (DSB) at a LO frequency of 106 GHz.     

230 and 492 GHz low noise sis waveguide receivers employing tuned Nb/AlOx/Nb tunnel junctions

We report results on two full height waveguide receivers that cover the 200–290 GHz and 380–510 GHz atmospheric windows. The receivers are part of the facility instrumentation at the Caltech Submillimeter Observatory on Mauna Kea in Hawaii. We have measured receiver noise temperatures in the range of 20K–35K DSB in the 200–290 GHz band, and 65–90K DSB in the 390–510 GHz atmospheric band. In both instances low mixer noise temperatures and very high quantum efficiency have been achieved. Conversion gain (3 dB) is possible with the 230 GHz receiver, however lowest noise and most stable operation is achieved with unity conversion gain. A 40% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner full height waveguide mixer block. The tuned Nb/AlO _x /Nb tunnel junctions incorporate an “end-loaded” tuning stub with two quarter-wave transformer sections to tune out the large junction capacitance. Both 230 and 492 GHz SIS junctions are 0.49µm² in size and have current densities of 8 and 10 kA/cm² respectively. Fourier Transform Spectrometer (FTS) measurements of the 230 and 492 GHz tuned junctions show good agreement with the measured heterodyne waveguide response.     

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.     

High linearity CMOS mixer for domotic 5 GHz WLAN sliding-IF receivers

The present paper describes the design of a 1.1 GHz CMOS, fully differential, down conversion mixer to be used as a second down conversion mixer in an integrated transceiver for 5 GHz domotic WLAN. The circuit was implemented in a 0.35 μm SiGe BiCMOS technology and designed with the aim of getting high linearity without excessive reduction in the conversion gain. The obtained circuit exhibits a conversion gain of −1 dB and a third-order input intercept point of +10 dBm. Biased at 3 V, it dissipates 45 mW.     

Measured mixer noise temperature and conversion loss of a cryogenic Schottky diode mixer near 800 GHz

We accurately measured the noise temperature and conversion loss of a cryogenically cooled Schottky diode operating near 800 GHz, using the UCB/MPE Submillimeter Receiver at the James Clerk Maxwell Telescope. The receiver temperature was in the range of the best we now routinely measure, 3150 K (DSB). Without correcting for optical loss or IF mismatch, the raw measurements set upper limits ofT _M=2850 K andL _M=9.1 dB (DSB), constant over at least a 1 GHz IF band centered at 6.4 GHz with an LO frequency of 803 GHz. Correction for estimated optical coupling and mismatch effects yieldsT _M=1600 K andL _M=5.5 dB (DSB) for the mixer diode itself. These values indicate that our receiver noise temperature is dominated by the corner cube antenna's optical efficiency and by mixer noise, but not by conversion loss or IF mismatch. The small fractional IF bandwidth, measured mixer IF band flatness from 2 to 8 GHz, and similarly good receiver temperatures at other IF frequencies imply that these values are representative over a range of frequencies near 800 GHz.     

Simulated performance of SIS and SIN junctions as heterodyne receivers in waveguide and open antenna mixer mounts

Tucker's quantum theory of mixing (in the 3-port approximation) is employed to calculate the gain over a wide range of frequencies of model mixers employing SIS and SIN junctions with both real and idealI–V characteristics. A comparison is made between the performance of junctions in waveguide and open antenna mounts. It is concluded that ideal junctions give gain 1.5 to 2 times higher than real ones, SIS junctions have gain approximately three times greater than otherwise similar SIN junctions, and that junction areas need to be typically three times smaller in open antenna structures to provide comparable gain to those in waveguide mounts.     

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.