A 385–500 GHz SIDEBAND-SEPARATING (2SB) SIS MIXER BASED ON A WAVEGUIDE SPLIT-BLOCK COUPLER

We have developed a 385–500 GHz sideband-separating (2SB) mixer, which is based on a waveguide split-block coupler at the edge of the H-plane of the 508 μm × 254 μm (WR 2.0) waveguide, for the Atacama Large Millimeter/submillimeter Array (ALMA). An RF/LO coupler, which contains an RF quadrature hybrid, two LO couplers, and an in-phase power divider, was designed with the issue of mechanical tolerance taken into account. The RF/LO coupler was measured optically with a microscope and electrically with a submillimeter vector network analyzer. The image rejection ratio (IRR) and the single-sideband (SSB) noise temperature of the receiver using the RF/LO coupler have also been measured. The IRR was found to be larger than 8 dB and typically ～ 12 dB in the 385–500 GHz band. The SSB noise temperature of this receiver is 80 K at the band center, which corresponds to 4 times the quantum noise limit (hf/k) in SSB, and 250 K at the band edges.     

Performance of the Production Band 3 receivers (84-116 GHz) for the Atacama Large Millimeter Array (ALMA)

This paper presents the performance of production Band 3 receivers (84-116 GHz) for the Atacama Large Millimeter Array (ALMA) that operate in Chile at 5000 m altitude. The fabrication, and testing of a total of 73 receivers necessitated stringent quality control during assembly and custom designed automated test set for accurate and reproducible measurement results. Interfaces to the ALMA receiver system are described in details. The average single side band noise temperature of band 3 production receivers is 33.2 K, with a minimum of 24.4 K and a maximum of 45.5 K. As for image rejection, the average is 18 dB, with a minimum at 12 dB and a maximum of 21 dB. Other performances with test methodology are described such as gain variation within the IF band, the gain and phase stability, gain compression, and beam patterns. This paper also describes the interfaces to the ALMA front end system, the testing methodology used, and the test results.     

ALMA Band 1 Optics (35–50 GHz): Tolerance Analysis,Effect of Cryostat Infrared Filters and Cold Beam Measurements

The Atacama Large Millimeter/Sub-millimeter Array (ALMA) is currently the largest (sub-)mm wave telescope in the world and will be used for astronomical observations in all atmospheric windows from 35 to 950 GHz when completed. The ALMA band 1 (35–50 GHz) receiver will be used for the longest wavelength observations with ALMA. Because of the longer wavelength, the size of optics and waveguide components will be larger than for other ALMA bands. In addition, all components will be placed inside the ALMA cryostat in each antenna, which will impose severe mechanical constraints on the size and position of receiver optics components. Due to these constraints, the designs of the corrugated feed horn and lens optics are highly optimized to comply with the stringent ALMA optical requirements. In this paper, we perform several tolerance analyses to check the impact of fabrication errors in such an optimized design. Secondly, we analyze the effects of operating this optics inside the ALMA cryostat, in particular the effects of having the cryostat IR filters placed next to the band 1 feed horn aperture, with the consequent near-field effects. Finally, we report on beam measurements performed on the first three ALMA band 1 receivers inside test cryostats, which satisfy ALMA specifications. In these measurements, we can clearly observe the effects of fabrication tolerances and IR filter effects on prototype receiver performance.     

The Development of a Dual Channel SIS Receiver of Trao Telescope

We developed a low noise dual channel receiver with 100GHz and 150GHz band, which is used to make the simultaneous observation with two bands. The SIS mixers are used in both bands. The constructed dewar for the receiver has a performance with a vacuum of 10^?8torr and a temperature of 4.2K. The receiver noise temperature is 50K(DSB) for 100GHz band and 80K(DSB) for 150GHz band, respectively. In order to achieve the simultaneous observations, the quasioptical system is precisely designed, and also evaluated by measurements in the laboratory. The relative pointing offset between two bands is 3″. We have observed the various sources using the receiver since October 1998.     

A 210–280 GHz sis heterodyne receiver for the James Clerk Maxwell Telescope part I: Design and performance

We describe the design and performance of a 210–280 GHz SIS heterodyne receiver built for use on the Maxwell Telescope. The mixer utilises a lead alloy SIS tunnel junction, mounted in 4∶1 reduced height rectangular waveguide, and is tuned with a backshort in 2∶1 reduced height guide. The receiver has a receiver noise temperature of <200K (DSB) across the RF band from 210–270 GHz, with a best noise temperature measured in the laboratory of 113K (DSB) at 231 GHz. A prototype version of this receiver was successfully operated on the telescope in May 1989. By direct intercalibration with a Schottky diode receiver we deduced a best receiver noise temperature of 140K (DSB) at 245 GHz. Discrepancies between this figure and that derived from broad band thermal load calibration are discussed in the accompanying paper (Little et al., 1992, this issue).     

A Low-Noise Terahertz SIS Mixer Incorporating a Waveguide Directional Coupler for LO Injection

We have developed a low-noise heterodyne waveguide Superconductor-Insulator-Superconductor (SIS) mixer with a novel local oscillator (LO) injection scheme for the Atacama Large Millimeter/submillimeter Array (ALMA) band 10, over the frequency range 0.78–0.95 THz. The SIS mixer uses radio frequency (RF) and LO receiving horns separately and a waveguide 10 dB LO coupler integrated in the mixer block. The insertion loss of the waveguide and coupling factor of the coupler were evaluated at terahertz frequencies at both room and cryogenic temperatures. The double-sideband (DSB) receiver noise temperatures were below 330 K (7.5hf/k _B) at LO frequencies in the range 0.801–0.945 THz. The minimum temperature was 221 K at 0.873 THz over the intermediate frequency range of 4–12 GHz at an operating temperature of 4 K. This waveguide heterodyne SIS mixer exhibits great potential for practical applications, such as high-frequency receivers of the ALMA.     

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.     

Q-Band GaAs Bandpass Filter Designs for ALMA Band-1

We report on the design and experimental results of Q-band GaAs bandpass filters (BPFs) for the Atacama Large Millimeter/submillimeter Array (ALMA) band-1 receiver. The BPF is required to reject the lower side band from 15.3 to 29 GHz while retain minimum insertion loss across the passband of 31.3 to 45 GHz. In order to reduce the size and weight of receiver module effectively, on-chip BPF designs using the commercial GaAs process are proposed. The parallel-coupled BPF with quarter-wavelength resonators is adopted to achieve a wide fractional bandwidth of about 37%. In addition, the capacitive/inductive loaded coupled-line and the stepped-impedance resonator are used to largely reduce the filter size. Moreover, the cross-coupling effect is introduced to create transmission zeros, such that the required 25 dB stopband rejection below 29 GHz can be achieved. Specifically, two GaAs BPFs with sizes less than $1.24times 0.8 {rm mm}^{2}$ are demonstrated. They will be applied to the multi-chip-module version of ALMA band-1 receiver prototype for further system evaluation and feasibility studies.      

Development of a Submillimeter Double-Ridged Waveguide Ortho-Mode Transducer (OMT) for the 385–500 GHz Band

We present design and evaluations of a submillimeter double-ridged waveguide ortho-mode transducer (OMT) for ALMA Band 8 (385–500 GHz) cartridge receiver. The measured transmission loss of the OMT at 4 K was 0.4–0.5 dB according to noise measurements with an SIS mixer. The polarization isolation was measured to be larger than 29 dB from quasioptical measurements. The OMT consists of a Bϕifot junction and a double-ridged guide. A robust design with allowable mechanical errors of 20 μm has been demonstrated.     

A Fixed Tuned Low Noise 600-700 GHz SIS Receiver

We have designed and fabricated a fixed tuned low noise 600-700 GHz SIS mixer. Twin junctions connected in parallel was employed in the mixer design. A short microstrip tuning structure was used to minimize the RF signal loss at frequency above the energy gap. A receiver noise temperature below 200 K (without any loss correction) in the frequency range of 630 to 660 GHz was recorded. The lowest noise temperature of the receiver was 181 K (without any loss correction) at 656 GHz.     

A low noise SIS receiver covering the frequency range 215–250 GHz

We have developed a heterodyne receiver incorporating an SIS mixer for use on a radiotelescope operating at 1.3 mm wavelength. The mixer has a minimum conversion loss of <2 dB and contributes less than 60 K to a total double side band receiver noise temperature of about 80 K at 220 GHz and 230 GHz. To our knowledge this represents the lowest receiver noise ever reported in this frequency range.     

Design and analysis of a waveguide sis mixer above the gap frequency of niobium

We present the design and experimental data of an SIS waveguide mixer for frequencies from 760 to 820 GHz. We use a Nb-Al₂O₃-Nb junction with an integrated niobium tuning structure. The waveguide mixer block contains no adjustable tuning elements. Design criteria for lossy tuning structures, differing from the impedance matching techniques used in the lossless case, are described. We separate the influence of the intrinsic mixing properties of an SIS junction from the effects of the power coupling to the signal source on the overall noise. This allows us to derive the contributions of the optics, the losses in the stripline and the noise generated in the junction to the total receiver noise from the measurements. We achieve double sideband receiver noise temperatures of around 850 K at frequencies from 780 to 820 Ghz and 4.2 K operating temperature of the mixer. Cooling the mixer to 2.5 K results in an improvement of the receiver noise temperature by 150 to 200 K. The bandwidth is presently limited by the local oscillator. The mixer was successfully used in a dual channel receiver (440 to 490 GHz and 780 to 820 GHz) at the Submillimeter Telescope Observatory (SMTO) on Mount Graham, Arizona.     

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 850-GHz waveguide receiver employing a niobium SIS junctionfabricated on a 1-μm Si3N4 membrane

We report on a 850-GHz superconducting-insulator-superconducting (SIS) heterodyne receiver employing an RF-tuned niobium tunnel junction with a current density of 14 kA/cm², fabricated on a 1-μm Si₃N₄ supporting membrane. Since the mixer is designed to be operated well above the superconducting gap frequency of niobium (2Δ/h≈690 GHz), special care has been taken to minimize niobium transmission-line losses. Both Fourier transform spectrometer (FTS) measurements of the direct detection performance and calculations of the IF output noise with the mixer operating in heterodyne mode, indicate an absorption loss in the niobium film of about 6.8 dB at 822 GHz. These results are in reasonably good agreement with the loss predicted by the Mattis-Bardeen theory in the extreme anomalous limit. From 800 to 830 GHz, we report uncorrected receiver noise temperatures of 518 or 514 K when we use Callen and Welton's law to calculate the input load temperatures. Over the same frequency range, the mixer has a 4-dB conversion loss and 265 K±10 K noise temperature. At 890 GHz, the sensitivity of the receiver has degraded to 900 K, which is primarily the result of increased niobium film loss in the RF matching network. When the mixer was cooled from 4.2 to 1.9 K, the receiver noise temperature improved about 20% 409-K double sideband (DSB). Approximately half of the receiver noise temperature improvement can be attributed to a lower mixer conversion loss, while the remainder is due to a reduction in the niobium film absorption loss. At 982 GHz, we measured a receiver noise temperature of 1916 K     

Cryogenic Millimeter-Wave Receiver Using Molecular Beam Epitaxy Diodes

A millimeter-wave cryogenic receiver has been built for the 60-90-GHz frequency band using GaAs mixer diodes prepared by molecuIar beam epitaxy (MBE). The diodes are mounted in a reduced-height image rejecting waveguide mixer which is followed by a cooled parametric amplifier at 4.5-5.0 GHz. At a temperature of 18 K the receiver has a total single-sideband (SSB) system temperature of 312 K at a frequency of 81 GHz. This is the lowest system temperature ever reported for a resistive mixer receiver. The low-noise operation of the mixer is seen to be a result of 1) the short-circuiting of the noise entering the image port and 2) an MBE mixer diode with a noise temperature which is consistent with the theoretical shot noise from the junction and the thermal noise from the series resistance.     

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.     

ALMA North American Integration Center Front-End Test System

The Atacama Large Millimeter/submillimeter (ALMA) Array Front End (FE) system is the first element in a complex chain of signal receiving, conversion, processing and recording. 70 Front Ends will be required for the project. The Front End is designed to receive signals in ten different frequency bands. In the initial phase of operations, the antennas will be fully equipped with six bands. These are Band 3 (84–116 GHz), Band 4 (125–163 GHz), Band 6 (211–275 GHz), Band 7 (275–373 GHz), Band 8 (385–500 GHz) and Band 9 (602–720 GHz). It is planned to equip the antennas with the missing bands at a later stage of ALMA operations, with a few Band 5 (163–211 GHz) and Band 10 (787–950 GHz) receivers in use before the end of the construction project. The ALMA Front End is far superior to any existing receiver systems; spin-offs of the ALMA prototypes are leading to improved sensitivities in existing millimeter and submillimeter observatories. The Front End units are comprised of numerous elements, produced at different locations in Europe, North America and East Asia and are integrated at several Front End integration centers (FEIC) to insure timely delivery of all the units to Chile. The North American FEIC (NA FEIC) is at the National Radio Astronomy Observatory facility in Charlottesville, Virginia, USA. This paper describes the design and performance of the test set used at the NA FEIC to check the performance of the Front Ends, following integration and prior to shipment to Chile.     

A W-band microwave receiver for Te diagnosis in the tokamak TJ-1

This paper describes a 95 GHz receiver system based on a solid state oscillator which makes it possible to measure the electron temperature of the plasma in the tokamak TJ-1. We discuss the construction of the receiver system and its calibration, which is carried out by using a noise source in this band. The characteristics obtained for a 0,5 eV signal are presented. The results show that the receiver has a very low noise level, even for powers on the order of several picowatts.     

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.     

A low noise receiver for millimeter and submillimeter wavelengths

A broadband, low noise heterodyne receiver, suitable for astronomical use, has been built using a Pb alloy superconducting tunnel junction (SIS). The RF coupling is quasioptical via a bowtie antenna on a quartz lens and is accomplished without any tuning elements. In this preliminary version the double sideband receiver noise temperature rises from 205 K at 116 GHz to 375 K at 349 Ghz, and to 815 K at 466 GHz. This is the most versatile and sensitive receiver yet reported for sub-mm wavelengths.