The Expanded Very Large Array

In almost 30 years of operation, the Very Large Array (VLA) has proved to be a remarkably flexible and productive radio telescope. However, the basic capabilities of the VLA have changed little since it was designed. A major expansion utilizing modern technology is currently underway to improve the capabilities of the VLA by at least an order of magnitude in both sensitivity and in frequency coverage. The primary elements of the Expanded Very Large Array (EVLA) project include new or upgraded receivers for continuous frequency coverage from 1 to 50 GHz, new local oscillator, intermediate frequency, and wide bandwidth data transmission systems to carry signals with 16 GHz total bandwidth from each antenna, and a new digital correlator with the capability to process this bandwidth with an unprecedented number of frequency channels for an imaging array. Also included are a new monitor and control system and new software that will provide telescope ease of use. Scheduled for completion in 2012, the EVLA will provide the world research community with a flexible, powerful, general-purpose telescope to address current and future astronomical issues.Comment: Added journal reference: published in Proceedings of the IEEE, Special Issue on Advances in Radio Astronomy, August 2009, vol. 97, No. 8, 1448-1462 Six figures, one tabl

THz Ultra-wideband Passive Devices: Design, Simulation and Characterization

The last decades have seen an increasing interest in the THz research field, leading to a substantial improvement in technology and the emergence of new applications. In particular, the research on radio astronomy instrumentation has pushed millimeter and sub-millimeter technology boundaries and redefined state of the art.\ua0 Nonetheless, the requirements set for the next generation of radio astronomy receivers will demand remarkable technological development, especially in terms of RF and IF bandwidth. Addressing this need, the present licentiate thesis focuses on the design, simulation and characterization of ultra-wideband THz passive devices for the next generation of radio astronomy receivers. As THz receivers mixers are implemented with thin-film technology, waveguide to substrate transitions have a fundamental role in the performance and bandwidth of such systems. The critical requirements for these transitions are a proper impedance matching and the minimization of insertion loss. In this thesis, a waveguide to slotline superconducting transition based on substrateless finlines is proposed. The transition was designed for prospective broadband SIS mixer design in the frequency range 211-375 GHz. The experimental verification at cryogenic temperatures shows a remarkable fractional bandwidth of 55%. Although this transition represents a substantial improvement over existing designs, it is important to note that it transforms a waveguide propagation mode into slotline mode. For the majority of modern SIS mixers, microstrip line topology is the most suitable. Hence, the ongoing development is focused on broadband slotline to microstrip transitions. In this work, a slotline to microstrip transition based on Marchand Balun is designed, simulated and fabricated. The electromagnetic simulations showed promising results, and the cryogenic characterization at 4K is ongoing.For most modern polarization-sensitive THz receivers, 90\ub0 waveguide twists are essential interconnection parts. Since compactness and low insertion loss are critical requirements, single step-twists have emerged as an attractive solution. In this work, a novel compact wideband 90-degree twist for the 140-220 GHz band is presented. Furthermore, the proposed twist has a performance tolerant to small geometry variation, and hence it is especially suited for fabrication by direct milling. The experimental verification shows 44% fractional bandwidth with return loss better than 20 dB over most of the band

SuperCam, a 64-pixel heterodyne imaging array for the 870 micron atmospheric window

We report on the development of SuperCam, a 64 pixel, superheterodyne camera 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 advent of such a system will provide an order of magnitude increase in mapping speed over what is now available and revolutionize how observational astronomy is performed in this important wavelength regime. Unlike the situation with bolometric detectors, heterodyne receiver systems are coherent, retaining information about both the amplitude and phase of the incident photon stream. From this information a high resolution spectrum of the incident light can be obtained without multiplexing. SuperCam will be constructed by stacking eight, 1x8 rows of fixed tuned, SIS mixers. The IF output of each mixer will be connected to a low-noise, broadband MMIC amplifier integrated into the mixer block. The instantaneous IF bandwidth of each pixel will be ~2 GHz, with a center frequency of 5 GHz. A spectrum of the central 500 MHz of each IF band will be provided by the array spectrometer. Local oscillator power is provided by a frequency multiplier whose output is divided between the pixels by using a matrix of waveguide power dividers. The mixer array will be cooled to 4K by a closed-cycle refrigeration system. SuperCam will reside at the Cassegrain focus of the 10m Heinrich Hertz telescope (HHT). A prototype single row of the array will be tested on the HHT in 2006, with the first engineering run of the full array in late 2007. The array is designed and constructed so that it may be readily scaled to higher frequencies.Comment: 12 pages, 14 figures, to be published in the Proceedings of SPIE Vol. 6275, "Astronomical Telescopes and Instrumentation, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III

Millimeter-Wave MMICs and Applications

As device technology improves, interest in the millimeter-wave band grows. Wireless communication systems migrate to higher frequencies, millimeter-wave radars and passive sensors find new solid-state implementations that promise improved performance, and entirely new applications in the millimeter-wave band become feasible. The circuit or system designer is faced with a new and unique set of challenges and constraints to deal with in order to use this portion of the spectrum successfully. In particular, the advantages of monolithic integration become increasingly important. This thesis presents many new developments in Monolithic Millimeter-Wave Integrated Circuits (MMICs), both the chips themselves and systems that use them. It begins with an overview of the various applications of millimeter waves, including a discussion of specific projects that the author is involved in and why many of them demand a MMIC implementation. In the subsequent chapters, new MMIC chips are described in detail, as is the role they play in real-world projects. Multi-chip modules are also presented with specific attention given to the practical details of MMIC packaging and multi-chip integration. The thesis concludes with a summary of the works presented thus far and their overall impact on the field of millimeter-wave engineering.</p

CASIMIR: a submillimeter heterodyne spectrometer for SOFIA

The CAltech Submillimeter Interstellar Medium Investigations Receiver (CASIMIR) is a multichannel, heterodyne spectrometer being developed for the Stratospheric Observatory for Infrared Astronomy (SOFIA). It has a very high resolution, up to a million, over the submillimeter and far-infrared wavelength range of 150 to 600 micrometers , or 2.0 to 0.5 THz. CASIMIR is extremely well suited to the investigation of both the galactic and extragalactic warm, approximately 100 K, interstellar medium. A combination of advanced SIS and Hot Electron Bolometers receivers will be used to cover this frequency range with very high sensitivity. CASIMIR will use only solid state local oscillators, with quasioptical coupling to the mixers. We present a description of the instrument and its capabilities, including detailed discussions of the receivers, local oscillators and IF systems