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- Billade, Bhushan, 1982, et al.
(författare)
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Performance of the first ALMA Band 5 production cartridge
- 2011
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Ingår i: Proceedings of the 22nd International Symposium on Space Terahertz Technology, April 26-28th, 2011 - Tucson, Arizona, USA. ; , s. 56-56
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Konferensbidrag (refereegranskat)abstract
- We present performance of the first ALMA Band 5 production cartridge, covering RF frequencies from 163 GHz to 211 GHz. ALMA Band 5 is a dual polarization, sideband separation (2SB) receiver based on all Niobium (Nb) SuperconductorInsulator-Superconductor (SIS) tunnel junction mixer, providing 16 GHz of instantaneous RF bandwidth for the astronomy observations. The 2SB mixer for each polarization employs a quadrature layout. The sideband separation occurs at the output of the IF hybrid that has integrated bias-T for biasing the mixers, and is produced using superconducting thin film technology. Experimental verification of the Band 5 cold cartridge performed together with warm cartridge assembly, confirms the system noise temperature below 45 K, less than five quantum noise (5 hf/k) over most of the RF band, which is to our knowledge, the best results at these frequencies. The measurement of the sideband rejection indicates that the sideband rejection better than 10 dB over 90% of the observational band.
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| 2. |
- Nyström, Olle, 1979
(författare)
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Design, Characterization, and Calibration of Low-Noise Terahertz Receivers
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused on the field of instrumentation for radio-astronomy and atmospheric science, and specifically deals with problems such as optical design and its verification, horn antennas and receiver optics’ components, different aspects of measurement systems in order to characterize low-noise THz receivers, and its calibration techniques.Ultra low-noise Terahertz receivers, used in radio-astronomy, are typically coupled to the telescope system through relay optics that provides guiding of the signal to the receiver frontend with minimal loss. Any misalignments, beam truncation, and distortion in the optical system will introduce losses and degrade the overall noise performance of the system. It is therefore critical that the optical design could be verified through measurements. In this thesis the author presents a vector beam measurement system to create possibilities to accurately characterize the optical performance of multi-band receivers over a very wide frequency range. The developed beam measurement system employs a novel circuitry allowing the use of a single reference source, different frequency harmonics of which allow to generate the required RF and LO signals yielding the desired IF, while obtaining perfect phase-coherence and initial phase-noise cancellation. An advantage of such wideband measurement system is that it could be used in different projects, nearly independent on frequency. Implementation of the measurement system, covering 163 GHz to 500 GHz, for the APEX receiver - Swedish Heterodyne Facility Instrument (SHeFI) - and the ALMA Band 5 receiver cartridge is described. Apart from optical characterization, noise-, sideband rejection, amplitude- and phase stability, and gain saturation measurements of the receivers are the measurements performed within the very same measurement setup. The measurement setup includes all necessary hardware and achieves largely automatic measurements with in-built optimization procedures. Another part of the thesis describes the author’s work on design of horn antennas. The feed horn is one of the most critical components in an optical system since it has direct impact on the total system performance. Two horn designs are presented in this thesis, one profiled corrugated feed horn, where particle swarm optimization (PSO) was successfully employed in the design procedure. The PSO drastically reduces the computational time and provides a robust optimization in terms of finding global optimum. A second horn design, implemented within PHOCUS, the Swedish sounding rocket project, is used for two water vapour radiometers, 183 GHZ and 557 GHZ. These antennas are based on the Potter horn and designed to provide FWHM of 5° without any additional focusing elements. Apart from the antenna design, two different calibration systems for both the 183 GHz and the 557 GHz radiometers on the PHOCUS sounding rocket have been suggested, designed, verified and implemented. The calibration systems shall meet challenging requirements associated with the rocket platform such as acceleration, shock, vibrations, limited space, and short flight time.
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| 3. |
- Nyström, Olle, 1979, et al.
(författare)
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PHOCUS Radiometer Payload
- 2011
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Ingår i: Proceedings of the 22nd International Symposium on Space Terahertz Technology, Tucson, AZ, USA, April 26-28, 2011. ; , s. P-9
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Konferensbidrag (refereegranskat)abstract
- PHOCUS – Particles, Hydrogen and Oxygen Chemistry in the Upper Summer Mesosphere is a Swedish sounding rocket experiment with the main goal of investigating the upper atmosphere in the altitude range 50-110 km. This paper describes the radiometer instruments (SondRad) in the PHOCUS payload, which are intended to explore the water vapour concentration in connection with the appearance of noctilucent (night shining) clouds. The design of the radiometer system has been done in collaboration between Omnisys Instruments AB and the Group for Advanced Receiver Development (GARD) at Chalmers University of Technology where Omnisys was responsible for the design, implementation, and verification of the radiometers and backend and GARD was responsible for the optics and calibration systems. The radiometers cover the water absorption lines at 183 GHz and 557 GHz with 67 kHz backend resolution. The 183 GHz channel is a side-looking radiometer while the 557 GHz radiometer is placed along the rocket axis looking in the forward direction. Both channels employ sub-harmonically pumped Schottky mixers and FFT spectrometer back-ends. The 183 GHz channel employs a CW-pilot signal calibrating the entire receiving chain while the IF-chain of the 557 GHz channel is calibrated by injecting a signal from a calibrated noise source through a directional coupler. The instrument will collect complete spectra for both the 183 and 557 GHz with 300 Hz rate for the 183 GHz channel and 10 Hz for the 557 GHz channel for about 60 seconds reaching the apogee of the flight trajectory and 100 seconds after that. With lossless data compression using variable resolution over the spectrum, the data set is reduced to 2 x 12 MByte.
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