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大气传输窗口为1.0～1.6毫米的宽带探测器已经研制成功,它在麦克唐纳天文台(McDonald Observatory)的2.7米射电望远镜上用来观测天体。对于连续天体信号源的观测,相对的品质因素为“噪声等效温度”或δTrms。对于1秒的观测时间,目前的δTrms=0.25K。至此观测到的天体有太阳、月亮、金星、木星、3C_(273)和银河系中心。如果采用目前的探测器灵敏度在 NRAO 天文台的11米射电望远镜上观测3小时,强度为0.7流量单位、波长为1毫米的信号源,它产生的信噪比可能为1。探测器采用的是铌-锡点接触约瑟夫逊结(以下简称约氏结)。约氏结同轴地安装在直径为5毫米的多重模式圆柱腔体内,再通过探针与直径为5毫米的非标准圆波导偶合。圆波导一直伸到杜瓦瓶口的外面。采用宽带工作方式,来自天体信号源的连续辐射入射就会降低约氏结的临界电流。给约氏结偏置一个20欧姆的源电阻就可测量该结临界电流变化引起的偏压变化。采用两种斩波方式的目的是把约氏结上1毫米的入辐射射分开。对于光亮的天体信号源,如太阳和月亮,波导输入端的总功率斩波器能够交替地使辐射计的输入端开启和关闭。对于模糊的信号源,差动斩波器可将信号源与周围的天空背景分开。
A broadband detector with an atmospheric transmission window of 1.0 to 1.6 mm has been developed and used to observe objects on the 2.7-meter radio telescope at the McDonald Observatory. For continuous celestial source observations, the relative quality factor is “noise equivalent temperature” or δTrms. For 1 second observation time, the current δTrms = 0.25K. The celestial bodies so far observed include the Sun, the Moon, Venus, Jupiter, 3C_ (273) and the Milky Way Galaxy Center. If the current detector sensitivity is observed for 3 hours at the NRAO 11-meter radio telescope with a signal strength of 0.7 flow units and a wavelength of 1 millimeter, it may produce a signal-to-noise ratio of one. The detector is used niobium - tin point contact Josephson junction (hereinafter referred to as Junction). Yoshimitsu coaxially mounted in a 5 mm diameter multi-mode cylindrical cavity, and then through the probe with a diameter of 5 mm non-standard circular waveguide coupling. The circular waveguide stretches out of the mouth of Dewar. With broadband mode of operation, continuous incident radiation from celestial sources can reduce the critical current around the junction. To bias the junction of a 20 Ohm source resistance can measure the knot junction junction current changes caused by bias changes. The purpose of the two chopping methods is to separate the incident radiation of 1 mm on the Junction's knot. For bright celestial sources, such as the sun and the moon, the total power chopper at the input of the waveguide alternately turns the radiometer's input on and off. For ambiguous sources, the differential chopper separates the source from the surrounding sky background.