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To make best use of the exceptional good weather conditions at Chajnantor we developed CHAMP+, a two time seven pixel dual-color heterodyne array for operation in the 350 and 450 µm atmospheric windows. CHAMP+ uses state-of-the-art SIS-mixers provided by our collaborators at SRON. To maximize its performance, optical single sideband filter are implemented for each of the two subarrays, and most of the optics is operated cold (20K) to minimize noise contributions. The instrument can be operated remotely, under full computer control of all components. The autocorrelator backend, currently in operation with 2 × 1GHz of bandwidth for each of the 14 heterodyne channels, will be upgraded by a new technologies FFT spectrometer array in mid 2008. CHAMP+ has been commissioned successfully in late 2007. We will review the performance of the instrument "in the field," and present its characteristics as measured on-sky.
The Anomalous X‐ray Pulsar 4U 0142+61 is the only neutron star where it is believed that one of the long searched‐for ‘fallback’ disks has been detected in the mid‐IR by Wang et al. [1] using Spitzer. Such a disk originates from material falling back to the NS after the supernova. We search for cold circumstellar material in the 90 GHz continuum using the Plateau de Bure Interferometer. No millimeter flux is detected at the position of 4U 0142+61, the upper flux limit is 150 μJy corresponding to the 3σ noise rms level. The re‐processed Spitzer MIPS 24μm data presented previously by Wang et al. [2] show some indication of flux enhancement at the position of the neutron star, albeit below the 3σ statistical significance limit. At far infrared wavelengths the source flux densities are probably below the Herschel confusion limits.
Kinetic Inductance Detectors with Integrated Antennas for Ground and Space-Based Sub-mm Astronomy
(2009)
Very large arrays of Microwave Kinetic Inductance Detectors (MKIDs) have the potential to revolutionize ground and space based astronomy. They can offer in excess of 10.000 pixels with large dynamic range and very high sensitivity in combination with very efficient frequency division multiplexing at GHz frequencies. In this paper we present the development of a 400 pixel MKID demonstration array, including optical coupling, sensitivity measurements, beam pattern measurements and readout. The design presented can be scaled to any frequency between 80 GHz and >5 THz because there is no need for superconducting structures that become lossy at frequencies above the gap frequency of the materials used. The latter would limit the frequency coverage to below 1 THz for relatively high gap materials such as NbTiN. An individual pixels of the array consist of a distributed Aluminium CPW MKID with an integrated twin slot antenna at its end. The antenna is placed in the in the second focus of an elliptical high purity Si lens. The lens-antenna coupling design allows room for the MKID resonator outside of the focal point of the lens. The best dark noise equivalent power of these devices is measured to be NEP = 7×10-19 W/[square root]Hz and the optical coupling efficiency is around 30%, in which no antireflection coating was used on the Si lens. For the readout we use a commercial arbitrary waveform generator and a 1.5 GHz FFTS. We show that using this concept it is possible to read out in excess of 400 pixels with 1 board and 1 pair of coaxial cables.
Radio pulsars in relativistic binary systems are unique tools to study the curved space-time around massive compact objects. The discovery of a pulsar closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr A⋆, would provide a superb test-bed for gravitational physics. To date, the absence of any radio pulsar discoveries within a few arc minutes of Sgr A⋆ has been explained by one principal factor: extreme scattering of radio waves caused by inhomogeneities in the ionized component of the interstellar medium in the central 100 pc around Sgr A⋆. Scattering, which causes temporal broadening of pulses, can only be mitigated by observing at higher frequencies. Here we describe recent searches of the Galactic centre region performed at a frequency of 18.95 GHz with the Effelsberg radio telescope.
GREAT, the German REceiver for Astronomy at THz frequencies, has successfully passed its pre-shipment acceptance review conducted by DLR and NASA on December 4-5, 2008. Shipment to DAOF/Palmdale, home of the SOFIA observatory, has been released; airworthiness was stated by NASA. Since, due to schedule slips on the SOFIA project level, first science flights with GREAT were delayed to mid 2010. Here we present GREAT’s short science flight configuration: two heterodyne channels will be operated simultaneously in the frequency ranges of 1.25-1.50 and 1.82-1.91 THz, respectively, driven by solid-state type local oscillator systems, and supported by a wide suite of back-ends. The receiver was extensively tested for about 6 month in the MPIfR labs, showing performances compliant with specifications. This short science configuration will be available to the interested SOFIA user communities in collaboration with the GREAT PI team during SOFIA’s upcoming Basic Science flights.
We review the development of our digital broadband Fast Fourier Transform Spectrometers (FFTS). In just a few years, FFTS back-ends - optimized for a wide range of radio astronomical applications - have become a new standard for heterodyne receivers, particularly in the mm and sub-mm wavelength range. They offer high instantaneous bandwidths with many thousands spectral channels on a small electronic board (100 x 160 mm). Our FFT spectrometer make use of the latest versions of GHz analog-to-digital converters (ADC) and the most complex field programmable gate array (FPGA) chips commercially available today. These state-of-the-art chips have made possible to build digital spectrometers with instantaneous bandwidths up to 1.8 GHz and 8192 spectral channels.
We present our second generation of broadband Fast Fourier Transform Spectrometer (FFTS), optimized for a wide range of radio astronomical applications. The new digitizer and analyzer boards make use of the latest versions of GHz analogto-digital converters and the most complex field programmable gate array chips commercially available today. These state-ofthe-art chips have made possible to build digital spectrometers with instantaneous bandwidths up to 1.8 GHz and 8192 spectral channels.
Known and novel techniques are described to implement a Fast Fourier Transform (FFT) in hardware, such that parallelized data can be processed. The usage of both - real and imaginary FFT-input - can help saving hardware. Based on the different techniques, flexible to use FFT-implementations have been developed by combining standard FFT-components (partly IP) and are compared, according to their hardware utilization. Finally, applicability has been demonstrated in practice by a FFTimplementation with 8192 channels as part of a FPGAspectrometer with a total bandwidth of 1.5 GHz.
Superconducting heterodyne receiver has played a vital role in the high resolution spectroscopy applications for astronomy and atmospheric research up to 2THz. NbN hot electron bolometer (HEB) mixer, as the most sensitive mixer above 1.5THz, has been used in the Herschel space telescope for 1.4-1.9THz and has also shown an ultra-high sensitivity up to 5.3THz. Combined a HEB mixer with a novel THz quantum cascade laser (QCL) as local oscillator (LO), such an all solid-state heterodyne receiver provides the technology which can be used for any balloon-, air- and space-borne heterodyne instruments above 2THz. Here we report the first high-resolution heterodyne spectroscopy measurement using a gas cell and using such a HEB-QCL receiver. The receiver employs a 2.9THz metal-metal waveguide QCL as LO and a NbN HEB as a mixer. By using a gas cell filled with methanol (CH3OH) gas in combination with hot/cold blackbody loads as signal source, we successfully recorded the methanol emission line around 2.918THz. Spectral lines at different pressures and also different frequency of the QCL are studied.
Based on our reconfigurable FPGA spectrometer technology, we have developed a read-out system, operating in the frequency domain, for arrays of Microwave Kinetic Inductance Detectors (MKIDs). The readout consists of a combination of two digital boards: A programmable DAC-/FPGA-board (tone-generator) to stimulate the MKIDs detectors and an ADC-/FPGA-unit to analyze the detectors response. Laboratory measurement show no deterioration of the noise performance compared to low noise analog mixing. Thus, this technique allows capturing several hundreds of detector signals with just one pair of coaxial cables.
We report the status of a search for pulsars in the Galactic Centre, using a completely revised and improved high-sensitivity doublehorn system at 4.85-GHz. We also present calculations about the success rate of periodicity searches for such a survey, showing that in contrast to conclusions in recent literature pulsars can be indeed detected at the chosen search frequency.
Microwave Kinetic Inductance Detectors have great potential for large very sensitive detector arrays for use in, for example, ground and spaced based sub?mm imaging. Being intrinsically readout in the frequency domain, they are particularly suited for frequency domain multiplexing allowing 1000s of devices to be readout with one pair of coaxial cables. However, this moves the complexity of the detector from the cryogenics to the warm electronics. We present the use of a readout based on a Fast Fourier transform Spectrometer, showing no deterioration of the noise performance compared to low noise analog mixing while allowing high multiplexing ratios (>100). We present use of this technique to multiplex 44 MKIDs, while this and similar setups are regularly now being used in our array development. This development will help the realization of large cameras, particularly in the short term for ground based astronomy.
We discuss our recent discovery of the giant radio emission from the Crab pulsar at its high frequency components (HFCs) phases and show the polarization characteristic of these pulses. This leads us to a suggestion that there is no difference in the emission mechanism of the main pulse (MP), interpulse (IP) and HFCs. We briefly review the size distributions of the Crab giant radio pulses (GRPs) and discuss general characteristics of the GRP phenomenon in the Crab and other pulsars.