SCUBA-2 is a second generation, wide-field submillimetre camera under development for the James Clerk Maxwell Telescope. With over 12,000 pixels, in two arrays, SCUBA-2 will map the submillimetre sky up to 1000 times faster than the current SCUBA instrument to the same signal-to-noise. Many areas of astronomy will benefit from such a highly sensitive survey instrument: from studies of galaxy formation and evolution in the early Universe to understanding star and planet formation in our own Galaxy. Due to be operational in 2006, SCUBA-2 will also act as a "pathfinder" for the new generation of submillimetre interferometers (such as ALMA) by performing large-area surveys to an unprecedented depth. The baseline design, projected telescope performance and scientific impact of SCUBA-2 are discussed in the paper.

SCUBA-2 is a second generation, wide-field submillimeter camera under development for the James Clerk Maxwell Telescope. With over 12,000 pixels, in two arrays, SCUBA-2 will map the submillimeter sky ~1000 times faster than the current SCUBA instrument to the same signal-to-noise. Many areas of astronomy will benefit from such a highly sensitive survey instrument: from studies of galaxy formation and evolution in the early Universe to understanding star and planet formation in our own Galaxy. Due to be operational in 2006, SCUBA-2 will also act as a "pathfinder" for the new generation of submillimeter interferometers (such as ALMA) by performing large-area surveys to an unprecedented depth. The challenge of developing the detectors and multiplexer is discussed in this paper.

We describe the design and performance of Bolocam, a 144-element, bolometric, millimeter-wave camera. Bolocam is currently in its commissioning stage at the Caltech Submillimeter Observatory. We compare the instrument performance measured at the telescope with a detailed sensitivity model, discuss the factors limiting the current sensitivity, and describe our plans for future improvements intended to increase the mapping speed.

With ESO and Onsala Space Observatory as partners, the Max-Planck-Institut for Radioastronomie (MPIfR) is building a submillimeter telescope of 12 m diameter (APEX), to be placed on the ALMA site (Chajnantor) in Chile. The telescope will be a modified copy of that ALMA prototype antenna, which has been designed by Vertex. First light is foreseen for 2003. As a result of the excellent atmospheric conditions of the site, APEX will offer unique opportunities for submm astronomy in the southern hemisphere. Many kinds of astronomical reseach projects benefit from large format bolometer arrays, especially the search for early galaxies and QSOs at very high redshifts. Designed for this purpose, LABOCA, the large bolometer camera, will operate at a wavelength of 870 μm and is planned to be operational soon after first light of APEX.

We describe a procedure for modeling the optical behaviour of planar, bolometric imaging arrays. Arrays of this kind are being developed for the next generation of ground-based and space-borne, submillimetre-wave and far-infrared, astronomical telescopes. A unique feature of the scheme is that the partially coherent vector fields associated with the individual pixels are traced through the optical system simultaneously. Simultaneous tracing is achieved by propagating the second-order statistical properties of the total field. In the paper, we describe the theoretical basis of our method, and present the results of a number of illustrative simulations.

This paper reviews the design, modeling, and testing of feedhorn arrays coupled to bolometric detector arrays being developed for the ESA Herschel Space Observatory's SPIRE instrument. SPIRE will incorporate five arrays of silicon nitride micromesh bolometers, in three broadband photometers and two Fourier-Transform spectrometers covering 200-700 μm, with a total of 326 feedhorn-coupled bolometers. The precision feedhorn arrays are formed by close-packing individually fabricated conical feedhorns, which terminate in waveguides and integrating cavities. The detector array is efficiently packaged by mounting it between a metallized silicon backshort array and the feedhorn array, which encloses the bolometers in precisely tuned integrating cavities. The absorption efficiency, bandwidth, and cross talk were first investigated with numerical simulations of the electromagnetic fields, and then measured for prototype arrays in a test facility. This discussion describes the design goals, simulations, fabrication, and measurements of optical efficiencies, spectral properties, beam shapes, and cross talk between bolometers.

SHARC II is a background-limited 350 μm and 450 μm facility camera for the Caltech Submillimeter Observatory undergoing commissioning in 2002. The key component of SHARC II is a 12 × 32 array of doped silicon 'pop-up' bolometers developed at NASA/Goddard. Each 1 mm × 1 mm pixel is coated with a 400 Ω/square bismuth film and located λ/4 above a reflective backshort to achieve >75% absorption efficiency. The pixels cover the focal plane with >90% filling factor. At 350 μm, the SHARC II pixels are separated by 0.65 λ/D. In contrast to the silicon bolometers in the predecessor of SHARC II, each doped thermistor occupies nearly the full area of the pixel, which lowers the 1/f knee of the detector noise to <0.03 Hz, under load, at the bath temperature of 0.36 K. The bolometers are AC-biased and read in 'total power' mode to take advantage of the improved stability. Each bolometer is biased through a custom ~130 MΩ CrSi load resistor at 7 K and read with a commercial JFET at 120 K. The JFETs and load resistors are integrated with the detectors into a single assembly to minimize microphonic noise. Electrical connection across the 0.36 K to 4 K and 4 K to 120 K temperature interfaces is accomplished with lithographed metal wires on dielectric substrates. In the best 25% of winter nights on Mauna Kea, SHARC II is expected to have an NEFD at 350 μm of 1 Jy Hz^-1/2 or better. The new camera should be at least 4 times faster at detecting known point sources and 30 times faster at mapping large areas compared to the prior instrument.

The redshift (Z) and of Early Universe Spectrometer (ZEUS) is a long slit echelle grating spectrometer that we are constructing for use in the submillimeter (350μm, 450μm, and 610μm) windows on the James Clerk Maxwell Telescope (JCMT). ZEUS has a resolving power of R≡λ/ΔΛ~1000, optimized for detecting broad, faint lines from extragalactic sources. The detector is a 16×32 pixel array of pop-up bolometers equipped with superconducting transition edge sensors linked into a SQUID multiplexed readout. This array should provide the requisite sensitivity at ~300mK, a temperature easily achieved using a two stage ³He refrigerator. ZEUS is optimized to quickly obtain spectra of point sources over very broad bands in the submillimeter windows. In the 350μm window, ZEUS will provide an instantaneous 27 resolution element spectrum, for each of 16 spatial elements on the sky. The roughly 10% bandwidth 350μm window can therefore be covered with just four settings of the grating. Each pixel is mapped into 5" on the sky (roughly 1•λ/D at 350 μm), so that the field of view is 5"×80". At 610μm, the slit is opened to 12" (2.4 pixels) resulting in a resolving power of around 500. ZEUS can quickly change wavelength or telluric window, adapting well to the demanding weather conditions in the short submillimeter windows. To minimize the effects of stray background radiation, two cold cut-on filters are used, together with 300mK band pass filters mounted on a filter wheel. This filter train fully sorts the echelle grating order, blocking unwanted radiation, but with high submillimeter band transmission. The expected point source sensitivities for 370μm, 444μm, and 610μm are 2.7×10¹⁷ W m^-2Hz^-1/2, 1.2×10^-17 W m^-2Hz^-1/2, and 1.6×10^-17W m^-2Hz^-1/2, respectively. Our primary scientific objectives are to (1) Investigate Ultraluminous Infrared Galaxies (ULIGs) via their (CI) and mid-J CO line emission-what are the origins of their tremendous infrared (IR) luminosities? Why are some ULIGs weak in the 158 μm (CII) line? (2) Probe star formation in the early Universe using highly redshifted far-IR fine-structure line emission-especially that of the 158 μm (CII) line. How strong are starbursts in the early Universe? and (3) Provide redshifts for all 850 μm SCUBA sources, providing source distance, luminosity, and number counts as a function of z. What is the evolutionary history of starformation in the early Universe?

We have built a prototype submillimeter spectrometer, FIBRE, which is based on a helium-cooled scanning Fabry-Perot and superconducting transition edge sensor bolometers (TES). SQUID multiplexers are used to read out the individual detector pixels. The spectral resolving power of the instrument is provided by the Fabry-Perot spectrometer. The outgoing light from the Fabry-Perot passes onto a low resolution grating for order sorting. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Δλ/λ=1/7 at a resolution of ~1/1200 can be achieved. The spectral resolution is sufficient to resolve doppler broadened line emission from external galaxies. FIBRE operates in the 350 μm and 450 μm bands. These bands cover line emission from the important PDR tracers neutral carbon [CI] and carbon monoxide CO. The spectrometer was used at the Caltech Submillimeter Observatory to obtain the first ever astronomical observations using multiplexed arrays of superconducting transition edge bolometers.

Since 1997, CEA/DSM/DAPNIA/ Service d?Astrophysique in Saclay and CEA/DTA/LETI in Grenoble are developing filled Bolometer arrays sensitive in far infrared and submillimeter. These arrays are based on an all Silicon technology development, and are optimized for imaging in high photon background conditions. A 32 × 64 and a 16 × 32 pixels arrays are under development for the far infrared photometer in the PACS instrument, which is part of the Herschel payload. We present details of the design of these arrays. We describe the performance measurements obtained so far, and give some prospects for future application

We are presently developing large format photoconductor arrays for the Herschel Space Observatory and for the Stratospheric Observatory For Infrared Astronomy (SOFIA). These arrays are based on individual Ge:Ga detectors contained in integrating cavities which are fed by an array of light cones to provide for area-filling light collection in the focal plane of an instrument. In order to detect light at wavelengths > 120 μm, uniaxial stress has to be applied to each detector crystal. We have developed a method to efficiently stress an entire stack of detector elements which allows us to form two-dimensional arrays from an arbitrary number of linear detector modules. Each linear module is read out by a cryogenic readout electronics circuit which operates at 4 K and is mechanically integrated into the module. We have measured effective quantum efficiencies of the light cone / detector /read-out chain of > 30% under realistic background conditions. GaAs photoconductive detectors could extend the spectral response cut-off up to > 300 μm. In the past, a continuous progress in material research has led to the production of pure, lightly and heavily doped n-type GaAs layers using the liquid phase epitaxy technique (LPE). Sample detectors demonstrated the expected infrared characteristics of bulk type devices. Modeling of BIB detector types predicts an improved IR sensitivity due to the attainable higher doping of the infrared sensitive layer. However, the modeling gives also an estimate of the severe material requirements for the n-type blocking layer. With a new centrifugal technique for the LPE material growth we intend to achieve this goal. Technical details of this unique equipment, first results of the achieved material quality in the initial growth runs and future steps to optimize operational parameters are reported. If successful, this detector technology will be first implemented in our spectrometer FIFI LS for SOFIA.

We report on the development of arrays of Transition-Edge Sensor (TES) bolometers. We describe several architectures including planar-antenna-coupled, horn-coupled, and absorber-coupled devices. Antenna coupling can greatly simplify the fabrication of multi-frequency bolometer arrays compared to techniques in common use. Planar antennas are intrinsically polarization sensitive and are a promising technology for measurements of CMB polarization. We have designed a prototype device with a double-slot dipole antenna, integrated band-defining filters, and a membrane-suspended bolometer. A test chip has been constructed. We are developing 300-1000 element arrays of horn-coupled TES bolometers with spider-web absorbers for galaxy cluster searches using the Sunyaev-Zel'dovich effect. Finally, we describe a filled absorber-coupled array design that is built using a single silicon wafer. Such arrays are well suited for far-infrared and sub-millimeter observations such as those from SOFIA and future orbital missions.

The High resolution Airborne Wideband Camera (HAWC) and the Submillimeter High Angular Resolution Camera II (SHARC II) will use almost identical versions of an ion-implanted silicon bolometer array developed at the National Aeronautics and Space Administration's Goddard Space Flight Center (GSFC). The GSFC "Pop-Up" Detectors (PUD's) use a unique folding technique to enable a 12 × 32-element close-packed array of bolometers with a filling factor greater than 95 percent. A kinematic Kevlar suspension system isolates the 200 mK bolometers from the helium bath temperature, and GSFC - developed silicon bridge chips make electrical connection to the bolometers, while maintaining thermal isolation. The JFET preamps operate at 120 K. Providing good thermal heat sinking for these, and keeping their conduction and radiation from reaching the nearby bolometers, is one of the principal design challenges encountered. Another interesting challenge is the preparation of the silicon bolometers. They are manufactured in 32-element, planar rows using Micro Electro Mechanical Systems (MEMS) semiconductor etching techniques, and then cut and folded onto a ceramic bar. Optical alignment using specialized jigs ensures their uniformity and correct placement. The rows are then stacked to create the 12 × 32-element array. Engineering results from the first light run of SHARC II at the Caltech Submillimeter Observatory (CSO) are presented.

The High Frequency Instrument on the NASA/ESA Planck Surveyor, scheduled for launch in 2007, will map the entire sky in 6 frequency bands ranging from 100 GHz to 857 GHz to probe Cosmic Microwave Background (CMB) anisotropy and polarization with angular resolution ranging from 9' to 5'. The HFI focal plane will contain 48 silicon nitride micromesh bolometers operating from a 100 mK heat sink. Four detectors in each of the 6 bands will detect unpolarized radiation. An additional 4 pairs of detectors will provide sensitivity to linear polarization of emission at 143, 217 and 353 GHz. We describe the fabrication process used to meet the stringent mission requirements on sensitivity, speed of response and stability.

The next generation of far-infrared and submillimeter instruments require large arrays of detectors containing thousands of elements. These arrays will necessarily be multiplexed, and superconducting bolometer arrays are the most promising present prospect for these detectors. We discuss our current research into superconducting bolometer array technologies, which has recently resulted in the first multiplexed detections of submillimeter light and the first multiplexed astronomical observations. Prototype arrays containing 512 pixels are in production using the Pop-Up Detector (PUD) architecture, which can be extended easily to 1000 pixel arrays. Planar arrays of close-packed bolometers are being developed for the GBT and for future space missions. For certain applications, such as a slewed far-infrared sky survey, feedhorn-coupling of a large sparsely-filled array of bolometers is desirable, and is being developed using photolithographic feedhorn arrays. Individual detectors have achieved a Noise Equivalent Power (NEP) of ~10^-17 W/√Hz at 300mK, but several orders of magnitude improvement are required and can be reached with existing technology. The testing of such ultralow-background detectors will prove difficult, as this requires optical loading of below 1fW. Antenna-coupled bolometer designs have advantages for large format array designs at low powers due to their mode selectivity. We also present a design and preliminary results for an enhanced-dynamic-range transition edge sensor suitable for broadband ultralow-background detectors.

We present a design for multipixel, multiband submillimeter instrument: SAMBA (Superconducting Antenna-coupled, Multi-frequency, Bolometric Array). SAMBA uses antenna coupled bolometers and microstrip filters. The concept allows for a much more compact, multiband imager compared to a comparable feedhorn-coupled bolometric system. SAMBA incorporates an array of slot antennas, superconducting transmission lines, a wide band multiplexer and superconducting transition edge bolometers. The transition-edge film measures the millimeter-wave power deposited in the resistor that terminates the transmission line.

We describe the development of a frequency-domain multiplexer (MUX) to read out arrays of superconducting transition-edge sensors (TES). Fabrication of large-format arrays of these sensors is becoming practical; however, reading out each sensor in the array is a major instrumental challenge that is possibly solved by frequency-domain multiplexing. Each sensor is AC biased at a different frequency, ranging from 380 kHz to 1 MHz. The sensor signal amplitude-modulates its respective AC bias frequency. An LC filter associated with each sensor suppresses Johnson noise from the other sensors. The signals are combined at a current summing node and measured by a single superconducting quantum interference device (SQUID). The individual signals from each sensor are then lock-in detected by room temperature electronics. Test chips with fully lithographed LC filters for up to 32 channels have been designed and fabricated. The capacitance and inductance values have been measured and are close to the design goals. We discuss the basic principles of frequency-domain multiplexing, the design and testing of the test chips, and the implementation of a practical system.

We are developing superconducting direct detectors for submillimeter astronomy that can in principle detect individual photons. These devices, Single Quasiparticle Photon Counter (SQPC), operate by measuring the quasiparticles generated when single Cooper-pairs are broken by absorption of a submillimeter photon. This photoconductive type of device could yield high quantum efficiency, large responsivity, microsecond response times, and sensitivities in the range of 10^-20 Watts per root Hertz. The use of antenna coupling to a small absorber also suggests the potential for novel instrument designs and scalability to imaging or spectroscopic arrays. We will describe the device concept, recent results on fabrication and electrical characterization of these detectors, issues related to saturation and optimization of the device parameters. Finally, we have developed practical readout amplifiers for these high-impedance cryogenic detectors based on the Radio-Frequency Single-Electron Transistor (RF-SET). We will describe results of a demonstration of a transimpedance amplifier based on closed-loop operation of an RF-SET, and a demonstration of a wavelength-division multiplexing scheme for the RF-SET. These developments will be a key ingredient in scaling to large arrays of high-sensitivity detectors.

The Frequency Selective Bolometer (FSB) is a bolometer with a patterned frequency selective absorber, coupled with a band-reflecting backshort. The resulting unit absorbs in-band radiation, and passes out-of-band radiation. Thus a series of FSBs tuned to different bands packed in series in a light pipe forms a compact multi-band photometer. The compact form factor makes it an attractive detector for a mm-wave array camera. We have built and characterized prototypes that demonstrate this technology. We are now developing a set of FSBs for SPEED (the SPEctral Energy Distribution camera), an FSB array camera which will observe 4 pixels in 4 mm-wave spectral bands, to be used on the Heinrich Hertz Telescope and the Large Millimeter Telescope. These FSBs are fabricated on a free-standing SiN film with TES thermometers. We will discuss the design and performance of these detectors.

Cryogenic tests of a prototype superconducting nanowire bolometer are presented. The device has such low thermal conductance it should be sensitive when used as a direct detector. Because of the small size of the active area we anticipate that this bolometer may also be fast enough to be used as a wideband mixer.

We report on the characterization of bolometers fabricated at the Jet Propulsion Laboratory for the High Frequency Instrument (HFI) of the joint ESA/NASA Herschel/Planck mission to be launched in 2007. The HFI is a multicolor focal plane which consists of 48 bolometers operated at 100mK. Each bolometer is mounted to a feedhorn-filter assembly which defines one of six frequency bands centered between 100-857GHz. Four detectors in each of six bands are coupled to both linear polarizations and thus measure the total intensity. In addition, eight detectors in each of 3 bands (143, 217, and 353GHz)couple only to a single linear polarization and thus provide measurements of the Stokes parameters, Q and U, as well the total intensity. The detectors are required to achieve a Noise Equivalent Power (NEP) at or below the background limit (formula available in paper)for the telescope and time constants of a few ms, short enough to resolve point sources as the 5 to 9 arc-minute beams move across the sky in great circles at 1 rpm. The bolometers are tested at 100mK in a commercial dilution refrigerator with a custom built thermal control system to regulate the heat sink with precision (formula available in paper). The 100mK tests include dark electrical characterization of the load curves, optical and electrical measurement of the thermal time constants and measurement of the noise spectral density from 0.01 to 10Hz for up to 24 bolometers simultaneously.

A capacitively coupled hot-electron nanobolometer (CC-HEB) is the simplest and most effective antenna-coupled bolometer. The bolometer consists of a small absorber connected to the superconducting antenna by tunnel junctions. The tunnel junctions used for high-frequency coupling also give perfect thermal isolation of hot electrons in the small volume of the absorber. The same tunnel junctions are used for temperature measurements and electron cooling. This bolometer does not suffer from the frequency limitations in the submillimeter range due to the high potential barrier of the tunnel junctions as does the microbolometer with Andreev mirrors (A-HEB), which is limited by the superconducting gap. Theoretical analyses show that the two-junction configuration more than doubles the sensitivity of the bolometer in current-biased mode compared to the single-junction configuration used for A-HEB. Another important advantage of CC-HEB is its simple two-layer technology for sample fabrication. Samples were fabricated with an absorber made of a bilayer of Cr and Al to match the impedance of the antenna. Electrodes were made of Al and tunnel junctions were formed over the Al oxide layer. The coupling capacitances of the tunnel junctions, C ≈ 20 fF, in combination with the inductance of the 10 μm absorber create a bandpass filter with a central frequency around 300 GHz. Bolometers are integrated with log-periodic and double-dipole planar antennas made of Au. The temperature response of bolometer structures was measured at temperatures down to 256 mK. In our experiment we observed dV/dT=1.3 mV/K, corresponding to responsivity S=0.2.10⁹ V/W. For amplifier noise V_na=3nV/Hz^1/2 at 1 kHz the estimated total noise equivalent power is NEP=1.5.10^-17 W/Hz^1/2. The intrinsic bolometer self noise V_nbol=0.5 nV/Hz^1/2 corresponds to NEP=3.10^-18 W/Hz^1/2. For microwave evaluation of bolometer sensitivity we used a black body radiation source comprising a thin NiCr stimulator placed on the cold plate of cryostat in front of a CC-HEB attached to an extended hemisphere sapphire lens. This measurements were consistent with estimates based on the dc responsivity of the bolometer.

We have developed a bolometric receiver that is intrinsically sensitive to linear polarization for the purpose of making measurements of the polarization of the cosmic microwave background radiation. The receiver consists of a pair of co-located silicon nitride micromesh absorbers which couple anisotropically to linearly polarized radiation through a corrugated waveguide structure. This system allows background limited, simultaneous measurement of the Stokes I and Q parameters over ~30% bandwidths at frequencies from ~60 to 600 GHz. Since both linear polarizations traverse identical optical paths from the sky to the point of detection, the susceptibility of the system to systematic effects is minimized. The amount of uncorrelated noise between the two polarization senses is limited to the quantum limit of thermal and photon shot noise, while drifts in the relative responsivity to orthogonal polarizations are limited to the effect of non-uniformity in the thin film deposition of the leads and the intrinsic thermistor properties. Devices using NTD Ge thermistors have achieved NEPs of 2•10^-17 W/√Hz with 1/f knees below 100mHz at a base temperature of 270 mK. Numerical modelling of the structures has been used to optimize the bolometer geometry and coupling to optics. Comparisons of numerical results and experimental data are made. A description of how the quantities measured by the device can be interpreted in terms of the Stokes parameters is presented. The receiver developed for the Boomerang and Planck HFI focal planes is presented in detail.

We extend the concept of the superconducting quantum counter in order to develop a new quantum detector for submillimeter astronomy. The detector exploits a cumulative detection mechanism, in which the response appears due to successive formation of the normal spot and a resistive domain in a narrow strip carrying sub-critical supercurrent. The intrinsic recovery time of the counter is partly determined by diffusion of nonequilibrium electrons and, thus, depends on the energy of detected photons. Depending on the superconducting material used and operation conditions, such detector may have cut-off wavelengths for the single-photon regime ranging from terahertz waves to visible light and simultaneously provide a moderate energy resolution. We simulated performance of the background-limited submillimeter direct detector from Ti having the 100-micrometer cut-off wavelength, low dark count rate and intrinsic 10^-21 W Hz-^1/2 noise equivalent power for 4-K background radiation. We present first results obtained with a detector prototype fabricated from ultra-thin Nb film.

The Combined Array for Research in Millimeter-wave Astronomy (CARMA) is a 23-antenna heterogeneous millimeter array under construction in the White/Inyo Mountains of eastern California. CARMA will merge the existing Owens Valley and Berkeley-Illinois-Maryland Association arrays into a single instrument focusing on pure research, technology development and student training. A new high-altitude site will enable routine 205-265 GHz observing, and may allow observations in the 345 GHz window. Eight additional 3.5-m antennas from the University of Chicago will also be integrated into CARMA when not imaging the Sunyaev-Zel'dovich effect towards clusters of galaxies. At first light, the array will observe at 12, 3 and 1.3 mm using a mix of SIS and MMIC-based receivers. A new, highly flexible correlator incorporating reprogrammable FPGA technology will process configurable subsets of the antennas specified according to the science objectives. Leading-edge water vapor radiometers will be used to correct for atmospheric opacity and signal phase fluctuations. CARMA will be capable of both high resolution and wide-field imaging, covering a range of angular scales unmatched by any current or planned millimeter-wave instrument. The high sensitivity, sub-arcsecond angular resolution and excellent uv-coverage of CARMA will ensure major advances in studies of the universe. The array will provide high-fidelity resolved images of solar-system objects, protostars, protoplanetary disks, and galaxies both nearby and at high redshift - directly addressing many key research areas in astronomy and astrophysics.

Under development at the Caltech Submillimeter Observatory is a dual polarization, continuous comparison (correlation) receiver. The instrument has two beams on the sky; a reference and a signal beam. Using only cooled reflecting optics, two polarizing grids, and a quadrature hybrid coupler, the sky beams are coupled to four tunerless SIS mixers (both polarizations). The 4-8 GHz mixer IF outputs are, after amplification, correlated against each other. In principle, this technique results in flat baselines with very low RMS noise and is especially well suited for high redshift Galaxy work. At the same time an upgrade is planned to the existing facility heterodyne instrumentation. Dual frequency mode receivers are under development for the 230/460 GHz and 345/660 GHz atmospheric windows. The higher frequency receivers are implemented in a balanced configuration, which reduces both the LO power requirement and noise. Each mixer has 4 GHz of IF bandwidth and can be controled remotely. Not only do these changes greatly enhance the spectroscopic capabilities of the CSO, they also enable the observatory to be integrated into the Harvard-Smithsonian Submillimeter Array (SMA) as an additional baseline.

New astronomical and remote-sensing instruments require microwave spectrometers with modest spectral resolution over many gigahertz of instantaneous bandwidth. Applications include millimeter-wave searches for distant objects with poorly known redshifts, submillimeter and far-infrared observations of Doppler-broadened spectral lines from galaxies, and observations of pressure-broadened atmospheric lines. Wide bandwidths and the consequent stability requirements make it difficult to use general-purpose receiver and spectrometer architectures in these applications. We discuss analog auto- and cross-correlation lag spectrometers that are optimized for these observations. Analog correlators obtain their wide bandwidths by a combination of transmission line delays and direct voltage multiplication in transistor or diode mixers. We show results from a new custom transistor multiplier with bandwidth to 25 GHz. Stability becomes increasingly important as bandwidths broaden. We discuss system requirements for single-dish correlation radiometers, which have intrinsic high stability, and present results showing that analog cross-correlators are suitable backends for these receivers.

The present status of AOS development at KOSMA is discussed. A study of a new generation of AOS using the new Bragg-cell material "Rutil" is on the way, which is supposed to lead to spectrometers in the range of 4 GHz total bandwidth at an resolution of 2-3 MHz. A second alternative for a 4 GHz bandwidth spectrometer has been developed as an engineering model for the HIFI instrument aboard the ESA cornerstone mission "Herschel". It consists of an array-AOS with 1 GHz bandwidth of each of the four AOS bands at a resolution of 1 MHz. A hybrid system for an input between 4 and 8 GHz is setup, and various laboratory tests have demonstrated that this system is well suited for large bandwidth applications like with HIFI. For eventual future demand of even larger bandwidth, details of a new optical method for Rf-analysis are discussed. It consists of a modulated laser with one or two Fabry-Perot etalons to analyze the frequency distribution of the resulting laser sidebands. A bandwidth of several 10 GHz at moderate resolution can be achieved.

We present some detail of the waveguide probe and SIS mixer chip designs for a low-noise 180-300 GHz double-sideband receiver with an instantaneous RF bandwidth of 24 GHz. The receiver's single SIS junction is excited by a broadband, fixed-tuned waveguide probe on a silicon substrate. The IF output is coupled to a 6-18 GHz MMIC low-noise preamplifier. Following further amplification, the output is processed by an array of 4 GHz, 128-channel analog autocorrelation spectrometers (WASP II). The single-sideband receiver noise temperature goal of 70 Kelvin will provide a prototype instrument capable of rapid line surveys and of relatively efficient carbon monoxide (CO) emission line searches of distant, dusty galaxies. The latter application's goal is to determine redshifts by measuring the frequencies of CO line emissions from the star-forming regions dominating the submillimeter brightness of these galaxies. Construction of the receiver has begun; lab testing should begin in the fall. Demonstration of the receiver on the Caltech Submillimeter Observatory (CSO) telescope should begin in spring 2003.

This is to report on our development for a full-polarization receiver to detect comic microwave background in 85 to 105 GHz band. Two such receivers have been built and tested, and currently undergoing site-testing on Mauna Loa, Hawaii. Each receiver is a very sensitive coherent detector to operate in 85-105 GHz with full polarization capability. Most of the receiver front-end components, including feed-horn, ortho-mode transducer, and low-noise amplifiers, are located in a cryogenic environment. We have designed a MMIC sub-harmonic pumped mixer, operating at 42 GHz, for signal down-conversion. In order to detect faint polarization signals in microwave background, a wide base-band, 2 to 18 GHz, is specified in the receiver design, and the entire base-band will be correlated. The receiver design details and the lab test results will be described in this report.

We present the first results obtained with our new dual frequency SIS array receiver SMART The instrument is operational since September 2001 at the KOSMA 3m telescope on Gornergrat near Zermatt/Switzerland. The receiver consists of two 2×4 pixel subarrays. One subarray operates at a frequency of 490 GHz, the other one at 810 GHz. Both subarrays are pointed at the same positions on the sky. We can thus observe eight spatial positions in two frequencies simultaneously. For the first year of operation we installed only one half of each subarray, i.e. one row of 4 mixers at each frequency. The receiver follows a very compact design to fit our small observatory. To achieve this, we placed most of the optics at ambient temperature, accepting the very small sensitivity loss caused by thermal emission from the optical surfaces. The optics setup contains a K-mirror type image rotator, two Martin-Puplett diplexers and two solid state local oscillators, which are multiplexed using collimating Fourier gratings. To reduce the need for optical alignment, we machined large optical subassemblies monolithically, using CNC milling techniques. We use the standard KOSMA fixed tuned waveguide SIS mixers with Nb junctions at 490 GHz, and similar Nb mixers with Al tuning circuits at 810 GHz. We give a short description of the front end design and present focal plane beam maps, receiver sensitivity measurements, and the first astronomical data obtained with the new instrument.

DesertSTAR is a 7 beam, 345 GHz heterodyne array receiver for the Heinrich Hertz Telescope (HHT) on Mt. Graham, AZ. The instrument uses fixed-backshort Superconductor-Insulator-Superconductor (SIS) mixers with a broadband waveguide probe. Instantaneous bandwidths greater than 2 GHz can be achieved over the entire 345 GHz atmospheric window. A cryostat with a Joule-Thompson (JT) mechanical refrigerator allows continuous operation and 1.8W of cooling capacity at 4K, and provides the needed temperature stability for low-noise operation. Local Oscillator (LO) distribution is accomplished with a novel phase grating that yields high efficiency and power uniformity in a hexagonally symmetric geometry. The computer controlled bias system is an evolution of a proven design that is simple and portable to any computer platform. The 2 GHz Intermediate Frequency (IF) bandwidth allows the future addition of a wideband backend optimized for extragalactic observations, with ~1700 km/s of velocity coverage. We present measurements of receiver performance and plans for integration on the HHT.

A 350GHz 4 × 4 element heterodyne focal plane array using SIS detectors is presently being constructed for the JCMT. The construction is being carried out by a collaborative group led by the MRAO, part of the Astrophysics Group, Cavendish Laboratory, in conjunction with the UK-Astronomy Technology Centre (UK-ATC), The Herzberg Institute of Astrophysics (HIA) and the Joint Astronomy Center (JAC). The Delft Institute of Microelectronics & Sub-micron Technology (DIMES) is fabricating junctions for the SIS mixers that have been designed at MRAO. Working in conjunction with the 'ACSIS' correlator & imaging system, HARP-B will provide 3-dimensional imaging capability with high sensitivity at 325 to 375GHz. This will be the first sub-mm spectral imaging system on JCMT - complementing the continuum imaging capability of SCUBA - and affording significantly improved productivity in terms of speed of mapping. The core specification for the array is that the combination of the receiver noise temperature and beam efficiency, weighted optimally across the array will be <330K SSB for the central 20GHz of the tuning range. In technological terms, HARP-B synthesizes a number of interesting and innovative features across all elements of the design. This paper presents both a technical and organizational overview of the HARP-B project and gives a description of all of the key design features of the instrument. 'First light' on the instrument is currently anticipated in spring 2004.

The advent of large format (~100 pixel) spectroscopic imaging cameras at submillimeter wavelengths would fundamentally change the way in which astronomy is performed in this important wavelength regime. While the possibility of such instruments has been discussed for more than two decades, only recently have advances in mixer technology, device fabrication, micromachining, digital signal processing, and telescope design made the construction of such an instrument possible and economical. In our paper, we will present the design concept for a 10×10 heterodyne camera.

We are developing terahertz mixers to cover the highest frequency band ("6H") for the heterodyne instrument (HIFI) aboard the Herschel Space Observatory. The mixer will be optimized for operation at 1.8 THz, with an input bandwidth of at least 0.2 THz. Some of the key spectroscopic lines in this frequency band are the fine-structure transition of ionized carbon at 1.9 THz, and numerous rotational transitions of water vapor and other hydrides. The mixers will employ a superconductive hot-electron bolometer as the mixing element, for which we will use a diffusion-cooled niobium microbridge. This variant allows an IF bandwidth that meets the range required for HIFI's 4-8 GHz IF. The mixer will be operated at ~2 K bath temperature. The sensitivity requirement is a double sideband mixer noise temperature of T_mix / ν ~ 1,000 K / THz , which has been previously demonstrated with this type of mixer. The mixer is a quasioptical design, employing a twin-slot planar antenna mounted on the backside of an elliptical silicon lens. Initial measurements indicate that that these mixers can be adequately pumped with a solid-state 1.5 THz local-oscillator source. HEB mixers are extremely delicate and susceptible to environmental damage; we have therefore focused a good deal of attention to engineering a rugged, flyable mixer.

NbN hot- electron bolometer mixers have reached the level of 10hv/k in terms of the input noise temperature with the noise bandwidth of 4-6 GHz from subMM band up to 2.5 THz. In this paper we discuss the major characteristics of this kind of receiver, i.e. the gain and the noise bandwidth, the noise temperature in a wide RF band, bias regimes and optimisation of RF coupling to the quasioptical mixer. We present the status of the development of the mixer for Band 6 Low for Herschel Telescope.

We summarize our research activities on THz Nb diffusion-cooled hot electron bolometer (HEB) mixers, carried out at Space Research Organization Netherlands (SRON) and Delft University of Technology. This paper will include our understanding on the device physics of diffusion-cooled HEB mixers, noise and IF bandwidth measurements of waveguide mixers around 0.7 THz, and in particular recent measurements of Nb quasi-optical mixers at 0.64 and 2.5 THz. The waveguide devices demonstrate a receiver noise temperature of 900 K at 0.7 THz. The quasi-optical mixers show 1200 K at 0.64 THz and 4500 K at 2.5 THz and a maximum IF bandwidth of at least 5 GHz.

Bolometric receivers serve as direct detectors, photon counters and as heterodyne receivers in astronomical instruments. Heterodyne hot-electron bolometric mixers show record sensitivity for observation frequencies above a Terahertz. In this paper NbN phonon-cooled mixers, conversion gain, noise and stability are discussed based on device models including Andreev reflection and critical current effects. The geometry (4 μm wide, 0.4 μm long on a 35 Å thick film), critical current (as high as possible) and critical temperature (about 8.5K) of an optimum phonon-cooled bolometric receiver operated at 2 to 4 K is discussed. Smaller devices than the optimum show worse noise performance. Larger devices require too high local oscillator power.

Heterodyne receivers for applications in astronomy need quantum limited sensitivity. In instruments which are currently under development for SOFIA or Herschel superconducting hot electron bolometers (HEB) will be used to achieve this goal at frequencies above 1.4 THz. We present results of the development of a phonon-cooled NbN HEB mixer for GREAT, the German Receiver for Astronomy at Terahertz Frequencies, which will be flown aboard SOFIA. The mixer is a small superconducting bridge incorporated in a planar feed antenna and a hyperhemispherical lens. Mixers with logarithmic-spiral and double-slot feed antennas have been investigated with respect to their noise temperature, conversion loss, linearity and beam pattern. At 2.5 THz a double sideband noise temperature of 2200 K was achieved. The conversion loss was 17 dB. The response of the mixer was linear up to 400 K load temperature. The performance was verified by measuring an emission line of methanol at 2.5 THz. The measured linewidth is in good agreement with the linewidth deduced from pressure broadening measurements at millimeter wavelength. The results demonstrate that the NbN HEB is very well suited as a mixer for far-infrared heterodyne receivers.

We report on the status of the development of a 30% bandwidth tunerless SIS double-sideband mixer for the “Band 1” (480 GHz-630 GHz) channel of the heterodyne instrument (HIFI) of ESA’s Herschel Space Observatory, scheduled for launch in 2007. After exposing the main features of our mixer design, we present the performance achieved by the demonstration mixer, measured via Fourier Transform Spectroscopy and heterodyne Y factor calibrations. We infer from a preliminary mixer analysis that the mixer has very low, quantum-limited noise and low conversion loss. We also report on some pre-qualification tests, as we currently start to manufacture the qualification models and design the last iteration of masks for SIS junction production.

The assembly of superconducting millimeter and submillimeter-wave circuits often requires RF ground connections. These are usually made by soldering, wire bonding, conductive adhesive or conductive wire gaskets. The difficulty of assembly increases with frequency as chip dimensions and tolerances shrink. The assembly issues, and also the throughput requirements of large radio astronomy projects such as ALMA (Atacama Large Millimeter Array), suggest the need of a beam lead technology for these circuits. Beam lead processes are already established for silicon and gallium arsenide wafers. However, niobium circuits on quartz substrates present unique difficulties. SIS junctions introduce additional thermal and chemical constraints to process development. For quartz, wet etches are isotropic and dry etches with high etch rates require large ion energies. Therefore, it is difficult to develop a conventional process in which gold pads on the substrate surface are formed into beam leads by a backside etch. Instead we have developed a topside process in which, after the mixer circuits are completed, dicing cuts are made at the finished chip dimensions but only partly through the wafer. The dicing cuts are then filled with a sacrificial material in a non-CMP process, and planarized. Gold plated pads are then defined, overhanging the planarized cuts. The sacrificial material is then removed from these cuts, leaving the gold beam leads. The wafer is then backside lapped into the cuts to the desired thickness, separating the individual chips. We discuss the new planarization scheme developed for this beam lead process and compare a variety of sacrificial materials.

We report the successful operation of a 700 GHz SIS finline mixer employing a Nb tunnel junction and Nb transmission lines. In particular, we discuss the properties of a new mixer feed and the influence of tuning on the mixer performance. Experimental and simulation work shows that the performance of the mixer below the superconducting gap is strongly dependent on the electrical properties of the tuning stub, while at frequencies above the gap the mixer performance is dominated by both tuning and transmission line losses.

Frequency multiplier circuits based on planar GaAs Schottky diodes have advanced significantly in the last decade. Useful power in the >1 THz range has now been demonstrated from a complete solid-state chain. This paper will review some of the technologies that have led to this achievement along with a brief look at future challenges.

The Herschel Space Observatory (HSO), an ESA cornerstone mission with NASA contribution, will enable a comprehensive study of the galactic and the extra galactic universe. At the heart of this exploration are ultra sensitive coherent detectors for high-resolution spectroscopy. Successful operation of these receivers is predicated on providing a sufficiently powerful local oscillator (LO) source. Historically, a versatile space qualified LO source for frequencies beyond 500 GHz has been difficult if not impossible. This paper will focus on the effort under way to develop, build, characterize and qualify a LO chain to 1200 GHz (Band 5 on HSO) that is based on planar GaAs diodes mounted in waveguide circuits. State-of-the-art performance has been obtained from a three-stage (×2×2×3) multiplier chain that can provide a peak output power of 120 μW (1178 GHz) at room temperature and a peak output power of 190 μW at 1183 GHZ when cooled to 113 K. Implementation of this LO source for the Heterodyne Instrument for Far Infrared (HIFI) one of three instruments on HSO will be discussed in detail.

The development of widely tunable coherent frequency sources for application as local oscillators or simply as test equipment above 1 THz remains an impediment in receiver development and characterization. Photomixer sources have demonstrated sufficient power to pump SIS mixers to over 600 GHz and have demonstrated over 2.5 THz of bandwidth in a single device. First generation photomixer system solved the problem of frequency calibration, but failed to fully address the needed spectral purity required for heterodyne applications. A number of improved laser technologies are greatly simplifying the implementation and improving the spectral purity of photomixer systems, however a full system demonstration in the THz frequency range remains elusive. The current state of the art for photomixer based sources is explored in light of heterodyne local oscillator and coherent tests sources for antenna and component characterization at THz frequencies.

This paper summarizes the development of W Band amplifiers for the Local Oscillator (LO) chains for the Herschel HIFI (Heterodyne Instrument for Far Infrared) Instrument. Key amplifier development issues and their solutions are presented, which have been applied on the way to realizing stable, wide-band amplifiers capable of producing 240 mW or greater RF power output across the 71 to 106 GHz frequency range. The HIFI power amplifier design embodiment is based on an A-40 silicon-aluminum alloy package with six GaAs(Gallium Arsenide) HEMT(High Electron Mobility Transistors) MMIC(Monolithic Microwave Integrated Circuit) amplifier chips used in each amplifier. Development challenges addressed include: MMIC chip designs which initially had a variety of oscillation or "moding" propensities (mostly out-fo-band), signal splitter and combiner development and matching across the band, matching of chip characteristics for those chips installed in the parallel power combined arms of the amplifier, power output control and leveling. The chosen design solutions are presented, including device, component and material selection for amplifier operation at cryogenic temperatures. Room temperature and cryogenic (120 Kelvin) data is also shown for the amplifier.

Broadband fixed-tuned frequency multipliers in conjunction with broadband power amplifiers driven by frequency synthesizers are often used as local oscillator (LO) sources in the millimeter and submillimeter wave heterodyne instruments. At these frequencies the multipliers use Gallium Arsenide (GaAs) based Schottky varactor diodes as the nonlinear element, and like most other harmonic generators are susceptible to spurious signal interference. The state-of-the-art LO sources in the millimeter and submillimeter wavelengths use MMIC power amplifiers producing in excess of 250 mW of output power in the 100 GHz range, and they are used to drive the subsequent multiplier stages. Because of the high input power environment and the presence of noise in the system, the multipliers become vulnerable to spurious signal interference, either through the bias lines or through the RF port. As the spurious signals propagate through the multiplier chain, they generate inter-modulation products which might fall in the passband of the heterodyne instrument and seriously degrade its performance. The issues of frequency multiplier response to spurious signal interference and its effect on local oscillator performance in millimeter and submillimeter wave heterodyne instruments are investigated. Results of numerical harmonic balance simulations and laboratory experiments are presented here, and are found to show good agreement.

The sub-millimeter radiometers of the Herschel mission have very stringent requirements. The scientific goals require an instantaneous bandwidth of four GHz with very low noise, flat gain and low power dissipation. Short-term gain stability of the amplifier is important, because gain fluctuations could limit the sensitivity of the instrument. Besides, a highly reliable, low weight unit is required to be compatible with the space instrumentation standards. The amplifiers will be used in conjunction with HEB and SIS mixers in all 7 channels of the instrument. This paper describes the design, the special construction techniques and the results of the amplifiers built by Centro Astronómico de Yebes for the development model of the Herschel Heterodyne Instrument. The average noise temperature obtained in the 4-8 GHz band is 3.5 K, with a gain of 27 ±1.1 dB at an ambient temperature of 15 K and keeping the total power dissipation below the allowed 4 mW. Normalized gain fluctuations were carefully measured, being lower than 1.5·10^-4 Hz^-1/2 @ 1 Hz. Space qualification of the design is in progress.

This paper describes the design and development of a state-of-the-art dual-channel 183 GHz InP based Monolithic Microwave Integrated Circuit (MMIC) radiometer. This is the world's first reported monolithic radiometer that operates at 183 GHz enabling high precision micro-miniature sensing of atmospheric chemistry components in this band. The radiometer features the following key components: a plug-in front end low noise amplifier module utilizing a broadband InP MMIC that sets the system noise figure, a low loss waveguide diplexer module, waveguide-to-microstrip transitions fabricated on Z-cut quartz, a mechanical design that can be easily modified to be hermetic, dual-channel output allowing double sideband detection, and a combination of HEMT and HBT InP and GaAs MMIC active components.

We have designed and developed polarizers (or polarization converter, λ/4 phase shifter) using solid anisotropic medium of sapphire for millimeter and submillimeter waverange. Prototype polarizers made of sapphire was fabricated for 90 GHz band. The diameter and the thickness of the polarizers are 50mm and 2.8mm, respectively. Characteristics of this prototype polarizer have been measured. A simple and preliminary estimation of the insertion loss and the quantity of the phase shift at present is 0.4dB and 70°, respectively. These results show that polarizers using solid anistropic medium of sapphire are applicable for millimeter and submillimeter waverange.

A radio telescope is to be built at National Astronomical Observatory of China, which is designed to receive signal from pulsars for timing and relevant usage. The telescope will have an aperture of 50 m in diameter working at multi-wave bands of which the shortest wavelength is down to 13 cm. A fully steerable exposed scheme of the telescope within issued specification is studied. The design is essentially wheel and track style with 6 rollers grouped in three couples running on a track of 35 m in diameter. The main paraboloidal reflector is a mesh spanned with cramped stainless steel wire installed on a special "bowl-like" backup truss structure supported by 6 points on the bottom. The elevation motion is served by a couple of big spoke and brace welded gearwheels with "buoyant" unloading system for eliminating deflections due to deadweight and thermal effect. Besides the design of the main reflector back-up structure, this paper presents the special alidade layout, driving system, structural and wind hazard analyses, and includes servo control system before drawing a general conclusion.

Z-Spec is a broadband (195 - 310 GHz), direct-detection, millimeter-wave spectrometer with moderate resolution (R ~ 350) that we are building to observe CO rotational lines and atomic fine-structure lines in the recently discovered population of submillimeter galaxies. A large fraction of these sources cannot be identified optically and thus redshift determination is extremely difficult. The large instantaneous bandwidth of Z-Spec will allow measurement of redshifts up to z~4 via detection of two or more CO lines in a single spectrum. The spectrometer is based on a parallel-plate waveguide grating architecture that is substantially more compact than a conventional free-space grating system. The spectrometer and an array of 160 silicon nitride micromesh bolometers will be cooled to 100 mK to provide background-limited sensitivity. In addition to measuring the redshifts of sources discovered in submillimeter continuum surveys, Z-Spec will demonstrate a novel spectrometer concept well-suited for future far-infrared space missions.