降低滤波超表面在射电望远镜中噪声温度研究

Noise Temperature Reduction Study of Filtering Metasurfaces in Radio Telescopes

射电天文望远镜是天文观测、深空探测等研究的关键设备,提高其灵敏度、降低系统噪声温度具有重要意义。然而,由于分配给射电天文的频段受限,且常与其他业务共用,射电天文望远镜容易受到强烈的射频干扰。这些干扰进入射频接收机后,在低温放大器内产生交互调干扰、放大器饱和等问题,抬高了噪声本底,降低了射电望远镜对微弱信号的探测灵敏度。利用滤波超表面技术可以对射电天文射频干扰进行有效的抑制,但需要控制引入的额外噪声。提出了一种降低滤波超表面在射电天文望远镜中引入噪声温度的方法,分别研究了滤波超表面的耗散性损耗和反射损耗与噪声温度的关系,通过对不匹配反射波朝向的约束实现了噪声温度的最小化。应用本文提出的方法,可以使系统噪声温度降低35.4%。若将滤波超表面设置在致冷室内,可以实现仅0.11 K的额外噪声温度。

Radio astronomical telescope is a key system in astronomical observation,deep space exploration and other researches.It is of great significance to improve its sensitivity and reduce the system noise temperature.However,because the frequency band allocated to radio astronomy research is limited and often shared with other businesses,radio astronomy telescopes are vulnerable to strong radio frequency interference.After these interferences enter the RF receiver,intermodulation interference,amplifier saturation and other problems will occur in the low-temperature amplifier,raising its noise background and reducing the detection sensitivity of the radio telescope to weak signals.The filtering metasurface technology can effectively suppress radio astronomy radio frequency interference,but the additional introduced noise needs to be controlled.In this paper,we propose a method to reduce the noise temperature of filtering metasurface in radio astronomical telescope.We study the relationship between the dissipative loss and reflection loss of filtering metasurface and its noise temperature,and minimize the noise temperature by restricting the direction of mismatched reflections.Using the method proposed in this paper,the system noise temperature can be reduced by 35.4%.If the filtering metasurface is set in the cooling chamber,an additional noise temperature of only 0.11 K can be achieved.