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19 th International Symposium on Space Terahertz Technology 9-7 Measurement of Emissivity of the ALMA Antenna Panel at 840 GHz Using NbN-Based Heterodyne SIS Receiver S. V. Shitov 1,2 , J. Inatani 1 , W.-L. Shan 3 , M. Takeda 4 , A. V. Uvarov 2 and Y. Uzawa 1 1 National Astronomical Observatory of Japan, Mitaka, Japan 2 Institute of Radio-Engineering and Electronics, Moscow, Russia 3 Purple Mountain Observatory, Nanjing, China 4 Kobe Advanced ICT Research Center (KARC), Kobe, Japan The design of the dish for ALMA telescopes is subject to a number of special requirements. For example, focusing of the infrared portion of solar radiation must be restricted via diffused scattering from the surface of the panel, while RF loss, which cause the in-band noise emission, must be below 1%. These are somewhat contradictory requirements, since the surface of the antenna must have appropriate roughness (matte finish) providing the scattering of IR-radiation. The noise emission of a reflective surface is usually measured by a bolometer-based radiometer, which can provide a very high sensitivity [1]. Another technique is evaluation of the Q-factor of a resonator formed by the reflector under test. However, both techniques have their own drawbacks. A sensitive radiometer suffers usually from the low dynamic range while the resonant method assumes both precision design and adjustment of a resonator circuit. We tested ALMA Band-10 heterodyne SIS receiver as an antenna switching radiometer with 8 GHz instantaneous bandwidth (DSB receiver, IF band 4-8 GHz). The receiver is mounted within a vacuum 4-K cryostat and contains one of the experimental waveguide-type SIS mixers. The particular Band-10 SIS mixer employed the resonant type junction made of epitaxial NbN/AlN/NbN trilayer [2]. The noise temperature of the receiver referred to the antenna load is about 560 K (DSB) or about 330 K, if corrected for 25-µm Kapton beamsplitter. The receiver’s antenna switch is balanced to terminate the receiver input to a common 80-K absorber via two different paths. In this configuration, the emissivity of the surface is detected via the imbalance of the antenna switch occurring when the sample-under-test is inserted to produce the extra reflection. Since the large dynamic range of the receiver, the response can be calibrated with traditional 300-K and 80-K antenna loads. The value of (0.25±0.10)% has been measured for the sample of the antenna panel. To confirm both the measured value and the general feasibility of the method, samples made of phosphor bronze and stainless steel are measured using the same technique. The values of (0.30±0.10)% and (1.10±0.10)% are obtained for these samples correspondingly that is consistent with data obtained with bolometer radiometer [1]. The accuracy of the described technique will be discussed, that includes the effects of non-thermostatic environment. [1] A. E. Lange, S. Hayakawa, T. Matsumoto, H. Matsuo, H. Murakami, P. L. Richards, and S. Sato, "Rocket-borne submillimeter radiometer," Appl. Opt. 26, p. 401 (1987) [2] Y. Uzawa, Z. Wang; A. Saito, A. Kawakami, M. Takeda, “Development of a waveguide NbN-based SIS mixer in the 900-GHz band,” IEEE Transactions on Applied Superconductivity, Vol. 13, Issue 2, June 2003, pp. 692-695. 80
19 th International Symposium on Space Terahertz Technology Session 10 – THz Receivers / Backends 2 Wednesday 30 April 2008 10:50 – 12:50 Chair: Victor Belitsky 10:50 - 11:05 10-1 Spectrometers for (sub)mm radiometer Anders Emrich, applications Omnisys 11:05 - 11:20 10-2 Flight configuration of the TELIS Pavel Yagoubov, Instrument SRON 11:20 - 11:35 10-3 Performance Characterization of GISMO, Johannes Staguhn, a 2 Millimeter TES Bolometer Camera NASA/GSFC & used at the IRAM 30 m Telescope University of Maryland 11:35 - 11:50 10-4 350GHz band Sideband Separating Hirofumi Inoue, Receiver for ASTE University of Tokyo 11:50 - 12:05 10-5 Development of a Waveguide-Type Taku Nakajima, Dual-polarization Sideband-Separating Osaka Prefecture SIS Receiver System in 100 GHz Band University for the NRO 45-m Radio Telescope 12:05 - 12:20 10-6 A modular 16-pixel terahertz imager Mikko Leivo, VTT system applying superconducting microbolometers and room temperature read-out electronics 12:20 - 12:35 10-7 A novel heterodyne interferometer for Paul Grimes, millimetre and submillimetre astronomy Oxford University 12:35 - 12:50 10-8 A 600 GHz Imaging Radar for Goutam Chattopadhyay, Contraband Detection JPL/Caltech 81
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Program and Abstract Book - SRON

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