Hamdi Mani

Design of Cryogenic SiGe Low-Noise Amplifiers

This paper describes a method for designing cryogenic silicon-germanium (SiGe) transistor low-noise amplifiers and reports record microwave noise temperature, i.e., 2 K, measured at the module connector interface with a 50-Omega generator. A theory for the relevant noise sources in the transistor is derived from first principles to give the minimum possible noise temperature and optimum generator impedance in terms of dc measured current gain and transconductance. These measured dc quantities are then reported for an IBM SiGe BiCMOS-8HP transistor at temperatures from 295 to 15 K. The measured and modeled noise and gain for both a single-and two-transistor cascode amplifier in the 0.2-3-GHz range are then presented. The noise model is then combined with the transistor equivalent-circuit elements in a circuit simulator and the noise in the frequency range up to 20 GHz is compared with that of a typical InP HEMT.

Matched wideband low-noise amplifiers for radio astronomy

Two packaged low noise amplifiers for the 0.3-4 GHz frequency range are described. The amplifiers can be operated at temperatures of 300-4 K and achieve noise temperatures in the 5 K range (<0.1 dB noise figure) at 15 K physical temperature. One amplifier utilizes commercially available, plastic-packaged SiGe transistors for first and second stages; the second amplifier is identical except it utilizes an experimental chip transistor as the first stage. Both amplifiers use resistive feedback to provide input reflection coefficient S11<-10 dB over a decade bandwidth with gain over 30 dB. The amplifiers can be used as rf amplifiers in very low noise radio astronomy systems or as i.f. amplifiers following superconducting mixers operating in the millimeter and submillimeter frequency range.

The Next Generation BLAST Experiment

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) was a suborbital experiment designed to map magnetic fields in order to study their role in star formation processes. BLASTPol made detailed polarization maps of a number of molecular clouds during its successful flights from Antarctica in 2010 and 2012. We present the next-generation BLASTPol instrument (BLAST-TNG) that will build off the success of the previous experiment and continue its role as a unique instrument and a test bed for new technologies. With a 16-fold increase in mapping speed, BLAST-TNG will make larger and deeper maps. Major improvements include a 2.5-m carbon fiber mirror that is 40% wider than the BLASTPol mirror and ~3000 polarization sensitive detectors. BLAST-TNG will observe in three bands at 250, 350, and 500 μm. The telescope will serve as a pathfinder project for microwave kinetic inductance detector (MKID) technology, as applied to feedhorn-coupled submillimeter detector arrays. The liquid helium cooled cryostat will have a 28-day hold time and will utilize a closed-cycle 3He refrigerator to cool the detector arrays to 270 mK. This will enable a detailed mapping of more targets with higher polarization resolution than any other submillimeter experiment to date. BLAST-TNG will also be the first balloon-borne telescope to offer shared risk observing time to the community. This paper outlines the motivation for the project and the instrumental design.

Test and integration results from SuperCam: a 64-pixel array receiver for the 350 GHz atmospheric window

We report on both laboratory and telescope integration results from 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 In the past, all heterodyne focal plane arrays have been constructed using discrete mixers, arrayed in the focal plane. SuperCam reduces cryogenic and mechanical complexity by integrating multiple mixers and amplifiers into a single array module with a single set of DC and IF connectors. These modules are housed in a closed-cycle cryostat with a 1.5W capacity 4K cooler. The SuperCam instrument is currently undergoing laboratory testing with four of the eight mixer array modules installed in the cryostat (32 pixels). Work is now underway to perform the necessary modifications at the 10m Heinrich Hertz Telescope to accept the SuperCam system. SuperCam will be installed in the cassegrain cabin of the HHT, including the optical system, IF processing, spectrometers and control electronics. SuperCam will be integrated with the HHT during the 2009-2010 observing season with 32 pixels installed. The system will be upgraded to 64 pixels during the summer of 2010 after assembly of the four additional mixer modules is completed.

SuperCam: a 64 pixel heterodyne imaging spectrometer

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.

A 16-channel flex circuit for cryogenic microwave signal transmission

Heterodyne focal plane arrays used in the terahertz (THz) regime currently require a discrete set of rigid coaxial cables for the transmission of individual intermediate frequency (IF) signals. Consequently, the size of an array is limited to ~10s of pixels due to limited physical space and the complexity of assembly. In order to achieve an array with ~1000 pixels or greater, new interconnections must be developed capable of carrying multiple IF signals on a single carrier which is flexible, robust to noise, and terminated with a high density RF connector. As an intermediate step to the development of a ~1000 pixel heterodyne focal plane array, the Kilopixel Array Pathfinder Project (KAPPa) has developed a 16 channel IF flex circuit. Initially, design simulations were performed to evaluate various means of high-frequency (1~10 GHz) signal transmission, including microstrip, stripline and coplanar waveguides. The method allowing for the closest signal spacing and greatest resistance to radio frequency interference (RFI) was determined to be stripline. Designs were considered where stripline transitioned to microstrip in order to terminate the signal. As microstrip transmission lines are sensitive to RFI, a design featuring just stripline was evaluated. In both the stripline-to-microstrip and stripline-only designs, a three-layer copper-coated polyimide substrate was used. Signal transitions were accomplished by a signal carrying “hot” via passing through a series of three conductive pads, similar to work by Leib et al. (2010). The transition design essentially mimics a coaxial line, where the radial distance between the pads and the ground plane is optimized in order to achieve desired impedances. In simulation, 50 Ohm impedances were achieved throughout, with crosstalk and return loss limited to -30dB. Terminations are made via an array of Corning Gilbert G3PO blind mate connectors, which are small enough to match the 6mm pixel pitch of the KAPPa focal plane unit. In addition, circuits with SMA terminations were designed to enable straightforward testing with a vector network analyzer (VNA). Initial designs use ½ oz. (18 microns thickness) copper conductors. In the KAPPa application, the copper conductor is still suitable for cryogenic applications because of the very small cross section presented by the copper conductor. The stripline design allows the interconnect to be clamped securely for heat sinking with a copper clamp at 10K and 60K. Heat load to the 4K stage is limited to 10 mW if the circuit is heat sunk at 10K 150mm from the 4K focal plane. Future designs could be implemented with phosphor bronze as the conductor to further limit heat load at the expense of added loss.

The Design and Performance of a Wideband Radio Telescope for the GAVRT Program

A wideband Radio Telescope was designed and built for use in the Goldstone Apple Valley Radio Telescope (GAVRT) program. It uses an existing 34-m antenna retrofitted with a tertiary offset mirror placed at the vertex of the main reflector. It can be rotated to allow using two feeds that cover the 0.5-14-GHz band. The feed for 4.0-14.0 GHz is a cryogenically cooled, commercially available, open-boundary quadridge horn from ETS-Lindgren. Coverage from 0.5 to 4.0 GHz is provided by an uncooled lower frequency version of the same feed that uses a cooled LNA. The measured aperture efficiency is greater than 40% over much of the band.

DSS-28: a novel wide bandwidth radio telescope devoted to educational outreach

We have recently equipped the 34-meter DSS-28 radio telescope at the Goldstone Deep Space Communications Complex with a novel wide bandwidth radiometer and digital signal processor as part of the Goldstone Apple Valley Radio Telescope (GAVRT) educational outreach program operated by the Jet Propulsion Laboratory and the Lewis Center for Educational Research. The system employs a cryogenically cooled wide bandwidth quad-ridge feed and InP low noise amplifiers to achieve excellent noise performance from 2.7 to 14 GHz; a fractional bandwidth better than 4:1. Four independently tunable dual-polarization receivers each down-convert a 2 GHz block to baseband, providing access to 8 GHz of instantaneous bandwidth. A flexible FPGA-based signal processor has been constructed using CASPER FPGA hardware and tools to take advantage of this enormous bandwidth. This system demonstrates many of the enabling wide bandwidth technologies that will be crucial to maximizing the utility of future large centimeter-wavelength arrays, in particular the Square Kilometer Array. The GAVRT program has previously used narrow bandwidth total power radiometers to study flux variability of quasars and the outer planets. The versatility of DSS-28 will enable other projects including spectroscopy and SETI. Finally, the wide instantaneous bandwidth available makes this system uniquely suited for studying transient radio pulses. A configuration of the digital signal processor has been developed which provides the capability of recording a burst of raw baseband voltage data triggered by a real-time incoherent dedispersion system which is very sensitive to pulses from a known source, such as the Crab Nebula pulsar.

Instrumental performance and results from testing of the BLAST-TNG receiver, submillimeter optics, and MKID detector arrays

Polarized thermal emission from interstellar dust grains can be used to map magnetic fields in star forming molecular clouds and the diffuse interstellar medium (ISM). The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) flew from Antarctica in 2010 and 2012 and produced degree-scale polarization maps of several nearby molecular clouds with arcminute resolution. The success of BLASTPol has motivated a next-generation instrument, BLAST-TNG, which will use more than 3000 linear polarization- sensitive microwave kinetic inductance detectors (MKIDs) combined with a 2.5 m diameter carbon fiber primary mirror to make diffraction-limited observations at 250, 350, and 500 µm. With 16 times the mapping speed of BLASTPol, sub-arcminute resolution, and a longer flight time, BLAST-TNG will be able to examine nearby molecular clouds and the diffuse galactic dust polarization spectrum in unprecedented detail. The 250 μm detec- tor array has been integrated into the new cryogenic receiver, and is undergoing testing to establish the optical and polarization characteristics of the instrument. BLAST-TNG will demonstrate the effectiveness of kilo-pixel MKID arrays for applications in submillimeter astronomy. BLAST-TNG is scheduled to fly from Antarctica in December 2017 for 28 days and will be the first balloon-borne telescope to offer a quarter of the flight for “shared risk” observing by the community.

First observations with SuperCam and future plans

Supercam is a 345 GHz, 64-pixel heterodyne imaging array for the Heinrich Hertz Submillimeter Telescope (HHSMT). By integrating SIS mixer devices with Low Noise Ampliers (LNAs) in 8 - 1x8 pixel modules, the size needed for the cryostat and the complexity of internal wiring is signicantly reduced. All subsystems including the optics, cryostat, bias system, IF boxes, and spectrometer have been integrated for all 64 pixels. In the spring of 2012, SuperCam was installed on the HHSMT for an engineering run where it underwent system level tests and performed rst light observations. In the fall of 2012 SuperCam will begin a 500 square degree survey of the Galactic Plane in 12CO J=3-2. This large-scale survey will help answer fundamental questions about the formation, physical conditions, and energetics of molecular clouds within the Milky Way. The data set will be available via the web to all interested researchers.