Showing papers by "Sander Weinreb published in 2008"

SiGe HBT X-Band LNAs for Ultra-Low-Noise Cryogenic Receivers

Abstract: We report results on the cryogenic operation of two different monolithic X-band silicon-germanium (SiGe) heterojunction bipolar transistor low noise amplifiers (LNAs) implemented in a commercially-available 130 nm SiGe BiCMOS platform. These SiGe LNAs exhibit a dramatic reduction in noise temperature with cooling, yielding of less than 21 K (0.3 dB noise figure) across X-band at a 15 K operating temperature. To the authors' knowledge, these SiGe LNAs exhibit the lowest broadband noise of any Si-based LNA reported to date.

Experimental cryogenic modeling and noise of SiGe HBTs

Abstract: SiGe devices are an exciting contender for extremely low noise, cryogenically cooled amplifiers. This paper begins with a procedure for extracting a simple equivalent circuit model capable of accurately describing SiGe HBT devices. Next, small-signal modeling results obtained for a 3×0.12×18um2 SiGe HBT at 15, 40, 77, 120, 200, and 300K are presented along with discussion of performance enhancements due to cooling of the device. Finally, the modeled noise performance is presented as a function of temperature and frequency using the concept of minimum cascaded noise temperature, a figure of merit which incorporates both noise temperature and gain.

Pre-HEAT: submillimeter site testing and astronomical spectra from Dome A, Antarctica

Abstract: Pre-HEAT is a 20 cm aperture submillimeter-wave telescope with a 660 GHz (450 micron) Schottky diode heterodyne receiver and digital FFT spectrometer for the Plateau Observatory (PLATO) developed by the University of New South Wales. In January 2008 it was deployed to Dome A, the summit of the Antarctic plateau, as part of a scientific traverse led by the Polar Research Institute of China and the Chinese Academy of Sciences. Dome A may be one of the best sites in the world for ground based Terahertz astronomy, based on the exceptionally cold, dry and stable conditions which prevail there. Pre-HEAT is measuring the 450 micron sky opacity at Dome A and mapping the Galactic Plane in the 13 CO J=6-5 line, constituting the first submillimeter measurements from Dome A. It is field-testing many of the key technologies for its namesake -- a successor mission called HEAT: the High Elevation Antarctic Terahertz telescope. Exciting prospects for submillimeter astronomy from Dome A and the status of Pre-HEAT will be presented.

SuperCam: a 64 pixel heterodyne imaging spectrometer

Abstract: We report on the development of SuperCam, a 64 pixel imaging spectrometer designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The Supercam key project is a fully sampled Galactic plane survey covering over 500 square degrees of the Galaxy in 12CO(3-2) and 13CO(3-2) with 0.3 km/s velocity resolution.

The stratospheric terahertz observatory (STO): An LDB experiment to investigate the life cycle of the interstellar medium

Abstract: The Stratospheric Terahertz Observatory (STO) is a balloon-borne, 0.8-meter telescope designed to investigate the structure of the interstellar medium and the life cycle of interstellar clouds. In its first long duration flight, STO will use two, 4-beam HEB receiver arrays to survey part of the Galactic Plane in the [C II] line at 158 microns (the brightest spectral line in the Galaxy) and the [N II] line at 205 microns (a tracer of the star formation rate). At ~1' angular resolution and < 1 km/s velocity resolution, STO will detect every interstellar cloud with AV > 0.3 in the surveyed region, and, through excitation and kinematic diagnostics provided by [C II] and [N II] line emission, will illustrate how atomic and molecular clouds are formed and dispersed in the Galaxy. STO will make 3dimensional maps of the structure, dynamics, turbulence, energy balance, and pressure of the Milky Way's Interstellar Medium (ISM), as well as the star formation rate. In future flights, STO will observe the important far-infrared lines of [O I], [N II], and HD. I. SCIENCE GOALS AND OBJECTIVES STO will provide a comprehensive understanding of the inner workings of our Galaxy by exploring the connection between star formation and the life cycle of interstellar clouds. We will study the formation of molecular clouds from diffuse atomic gas, the feedback of high mass star formation on the lives of atomic and molecular clouds, and the effect of these processes upon the global structure and evolution of the Galaxy. The detailed understanding of star formation and evolution of stars and gas in the Galaxy is directly relevant to star formation in other galaxies. The nature of the feedback mechanism of massive star formation with its interstellar environment is pivotal to the evolution of galaxies. In its first flight, STO addresses the following high priority goals: 1. Determine the life cycle of Galactic interstellar gas. 2. Study the creation and disruption of star-forming clouds in the Galaxy. 3. Determine the parameters that affect the star formation rate in a galaxy. 4. Provide templates for star formation and stellar/interstellar feedback in other galaxies. STO will utilize two heterodyne receiver arrays to produce a total of eight ~1' pixels in the focal plane, each with 1024 spectral channels. In the first long duration (10-14 day) flight, STO will map a 35 square degree area (-20 > l > -55; |b| < 1, see Figures 1 and 2) spanning the Molecular Ring, the Crux-Scutum-Centaurus spiral arm, and at least one interarm region. Two deeper, 1/2 square degree maps will be performed within the larger survey in both arm and interarm regions. STO has the sensitivity to detect and the ability to resolve spectrally and spatially all Giant Molecular Clouds (GMCs), all significant HII regions, and all cold neutral medium (CNM) atomic clouds with AV > 0.3 mag in the surveyed region. The STO heterodyne receivers provide sub-km/s velocity discrimination and sufficient bandwidth to detect and resolve line emission from every Galactic cloud in the surveyed region. The data product will be a high fidelity database of spatially and velocity resolved far-infrared [C II] 158 micron and [N II] 205 micron fine-structure line emission in the Galaxy. 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April 2008

A 0.5–20GHz quadrature downconverter

Abstract: A quadrature downconverter with 4 GHz IF bandwidth and working over the 0.5-20 GHz RF frequency range has been designed, fabricated, and tested. The downconverter uses a frequency doubling and dividing scheme to generate quadrature local oscillator signals from 0.5-17 GHz and a pair of Gilbert-cell mixers to perform downconversion. When the IF outputs are combined with a commercial quadrature hybrid, the mixer achieves an image rejection ratio greater than 35 dB over the entire band with no on-chip calibration or tuning. The active die area is approximately 0.5times1 mm2.

Integration of IF Amplifiers with NbTiN SHEB Mixers

Abstract: For the 1.4 THz and 1.9 THz channels of the GREAT instrument for SOFIA we have developed waveguide mixers with NbTiN superconducting Hot Electron Bolometer (SHEB) devices on low stress silicon nitride membranes. Comparable mixers will also be used in the balloon-borne Stratospheric Terahertz Observatory (STO). In the current baseline approach for these receivers, the mixer is connected to the low noise IF amplifier by a narrow-band (1.2–1.8 GHz) cryogenic isolator to prevent interactions between the 1–2 GHz amplifier and the mixer. Previous tests have indicated that an isolator is necessary for a stable receiver performance with minimal variations of noise and gain vs. IF frequency. Unfortunately, the isolator has the disadvantage that a significant fraction of the potential IF bandwidth of the mixer and low noise IF amplifier is wasted.

Large Format Heterodyne Arrays for Terahertz Astronomy

Abstract: For future ground, airborne and space based single aperture telescopes, multipixel heterodyne imaging arrays are necessary to take full advantage of platform lifetime, and facilitate science requiring wide field spectral line imaging. A first generation of heterodyne arrays with ~10 pixels has already been constructed, i.e. CHAMP, SMART, HERA, DesertStar, PoleStar and HARP. Our group is now constructing SuperCam, a 64 pixel heterodyne array for operation in the 350 GHz atmospheric window. This instrument will realize another order of magnitude increase in array pixel count. Several new techniques were used for SuperCam to maximize integration and modularity. Unlike other SIS array receivers, SuperCam is built around 8 pixel linear mixer modules, rather than independent mixer blocks. These modules house 8 single ended waveguide mixers with SOI substrate SIS devices. Each device is tab bonded to a MMIC based LNA. These modules dissipate only 8 mW of heat, while still maintaining 5 K IF noise temperature and 32 dB gain. Blind mate IF and DC connectors allow each module to be inserted in or removed from the focal plane as a unit. The modules are machined using a state-of-the-art CNC micromilling machine acquired specifically for this project. IF signals are processed by 8 channel IF downconverter boards, which provide gain, baseband downconversion and IF total power monitoring. A real-time FFT spectrometer implemented with high speed ADCs and Xilinx 4 FPGAs produce spectra of the central 250 MHz of each channel at 0.25 km/s spectral resolution. For arrays with an additional order of magnitude increase in pixel count, several additional technical problems must be overcome. Kilopixel arrays will require advances in device fabrication, cryogenics, micromachining, IF processing and spectrometers. In addition, seemingly straightforward receiver systems will require new approaches to realize a kilopixel heterodyne array with manageable complexity and cost. Wire count and 4K heat load must all be reduced significantly compared to SuperCam. IF and DC cabling and interconnects may be replaced with multiconductor microstrip or stripline ribbon. Parallel biasing of LNAs, magnets and even SIS devices is feasible if device uniformity is good enough. IF processing will require further integration, possibly with integrated MMIC chips containing all parts of a IF downconversion chain. Continued advances in FFT spectrometers could allow processing many hundreds of gigahertz of IF bandwidth for a realizable cost. We present results from final SuperCam receiver integration and testing, and concepts for expanding heterodyne arrays to kilopixel scales in the future.

Dome A, Antarctica: Prospectives for terahertz astronomy from the ground

Abstract: Over a decade of site testing and operation of submillimeter telescopes has sh own that the high Antarctic Plateau (South Pole) and Chilean Atacama desert (Chajnantor) are e xceptional gr ound-based site s for submillimeter and terahertz astronomy. The highest sites at both locations (Dome A and the Ch ajnantor and Sairecabur summits) show great promise in yielding even more favorable conditions. To test the condi tions at Do me A, we have deployed Pre-HEAT, a 20 cm aperture submillim eter-wave telescope with a 660 GHz (450 micron) Schottky diode heterodyne re ceiver and digital F FT spe ctrometer for the Plateau Obse rvatory (P LATO) de veloped by the Unive rsity of New South Wales. In January 2008 it was deploy ed to Dome A, the summit of the Antarctic plateau, as part of a scientific tr averse le d by the Polar Re search Institute of China. Dome A may be one o f the best sites in the w orld for ground based Te rahertz astronomy, b ased on t he exceptionally cold, dr y and stable c onditions which pr evail there. Pr e-HEAT is meas uring the 450 micron sky opacity at Dome A and mapping the Galactic Plane in the 13 CO J=6-5 line, constituting the first s ubmillimeter measurements from Dome A. It is field-testing ma ny of th e key technologies for its name sake, a suc cessor mission c alled HEAT: the High Elevation An tarctic Terah ertz teles cope. Exc iting p rospects for submillimeter astronomy f rom Dome A and the status of Pre-HEAT will be presented.