| 1. |
- Belitsky, Victor, 1955, et al.
(författare)
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A new 3 mm band receiver for the Onsala 20 m antenna
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 580
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Tidskriftsartikel (refereegranskat)abstract
- A new receiver for the Onsala 20 m antenna with the possibility of being equipped with 3 mm and 4 mm bands has been built and the 3 mm channel has been commissioned during the Spring 2014. For single-dish operation, the receiver uses an innovative on-source/off-source optical switch. In combination with additional optical components and within the same optical layout, the switch provides two calibration loads (for the 3 mm and 4 mm channels), sideband rejection measurement, and tuning possibilities. The optical layout of the receiver employs all cold (4 K) offset elliptical mirrors for both channels, whereas the on-off switch employs flat mirrors only. The 3 mm channel employs a sideband separation (2SB) dual polarization receiver with orthomode transducer (OMT), 4-8 GHz intermediate frequency (IF), x? 2pol x? upper and lower sidebands (USB? +? LSB). The cryostat has four optical windows made of high density polyethylene (HDPE) with anti-reflection corrugations, two for the signal and two for each frequency band cold load. The cryostat uses a two-stage cryocooler produced by Sumitomo HI? RDK? 408D2 with anti-vibration suspension of the cold-head to minimize impact of the vibrations on the receiver stability. The local oscillator (LO) system is based on a Gunn oscillator with aphase lock loop (PLL) and four mechanical tuners for broadband operation, providing independently tunable LO power for each polarization. This paper provides a technical description of the receiver and its technology and could be useful for instrumentation engineers and observers using the Onsala 20 m telescope.
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| 2. |
- Hammar, Arvid, 1986, et al.
(författare)
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Optical Tolerance Analysis for the STEAMR Instrument
- 2013
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Ingår i: TWENTY-FOURTH INTERNATIONAL SYMPOSIUM ON SPACE TERAHERTZ TECHNOLOGY (ISSTT2013).
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Konferensbidrag (refereegranskat)abstract
- The optics of the STEAMR instrument is a complex system involving off-axis mirrors designed to achieve precise imaging of the 14 receiver channel beams from the far field to the corresponding feed horns. An initial optical design was generated by Swedish Space Corporation, which laid the framework for the subsequent IAP design that further developed the optical system to meet the mission performance requirements. Omnisys Instruments is now the prime contractor for the complete STEAMR instrument.Although simulations of the optics presently show good results, little is known about the sensitivity to mechanical errors, i.e. surface deviations and misalignments of the reflectors. This work encompasses a tolerance analysis for the complete optics chain consisting of a 28 reflector focal plane array (FPA) and 6 reflector relay optics. With six degrees of freedom for each reflector, the scale of the required mechanical tolerancing analysis is significant. The goal of this work is therefore to identify critical locations within the optics architecture that have the largest influence on performance.Being a multi-beam instrument, the optics requirements for STEAMR can be divided into two parts: pointing and beam quality. Pointing errors were analysed using the commercial software package ZEMAX, which offers built-in routines for performing Monte-Carlo simulations specifically for tolerancing problems. Beam quality, i.e. sidelobe levels, beam efficiency and polarization plane, were analysed using physical optics routines in GRASP. Simulations in both programs have been carried out using single element perturbation and Monte-Carlo simulations on the complete optics chain.In the first iteration of the analysis, all reflector surfaces were assumed to be perfect. In later analyses, surface errors were also added. Special attention was given to the 1.6 m x 0.8 m carbon fiber main reflector, which is the most sensitive in terms of errors in shape. By running the optical analysis in parallel and in close cooperation with the mechanical design, it has been possible to assume realistic errors for the different parts of the optics. Measurements of the feed horns done by IAP show excellent agreement with simulations, where sidelobe levels around -40 dB was predicted. Therefore, the beams of all feeds have been modelled as perfect Gaussians.
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| 3. |
- Hammar, Arvid, 1986, et al.
(författare)
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Optical Tolerance Analysis of the Multi-Beam Limb Viewing Instrument STEAMR
- 2014
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 4:6, s. 714-721
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Tidskriftsartikel (refereegranskat)abstract
- We report on an optical tolerance analysis of the submillimeter atmospheric multi-beam limb sounder STEAMR. Physical optics and ray-tracing methods were used to quantify and separate errors in beam pointing and distortion due to reflector misalignment and primary reflector surface deforma-tions. Simulations were performed concurrently with the man-ufacturing of a multi-beam demonstrator of the relay optical system which shapes and images the beams to their corresponding receiver feed horns. Results from Monte-Carlo simulations show that the inserts used for reflector mounting should be positioned with an overall accuracy better than 100 µm (~1/10 wavelength). Analyses of primary reflector surface deformations show that a deviation of magnitude 100 µm can be tolerable before deployment, whereas the corresponding variations should be less than 30 µm during operation. The most sensitive optical elements in terms of misalignments are found near the focal plane. This localized sensitivity is attributed to the off-axis nature of the beams at this location. Post-assembly mechanical measurements of the reflectors in the demonstrator show that alignment better than 50 µm could be obtained.
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