6.5-45.5GHz超宽带致冷接收机的关键技术研究

Cryogenic receiver is the most important equipment on the radio astronomical telescope. Lower noise and wider bandwidth are big goals for radio astronomy receiver technology development. The research target is building the ultra-wideband cryogenic receiver which has observation frequency range of 6.5 GHz to 45.5 GHz, could cover C/X/Ku/K/Ka/Q for a total six radio astronomy bands. The receiver noise temperature could be less than 40 Kelvin by cooling the whole feed and LNAs. Many flexible applications can be carried out, including more than 30 major spectral lines observation, more than 30 GHz bandwidth continuum spectrum observation, such as C/K/Q or X/Ka multiband observation. This project will focus on four key technologies, the ultra-wideband feed horn and polarizer, ultra-wideband cryogenic MMIC low noise amplifier, the large size low loss microwave vacuum window, the broadband high image reject converter and powerful synthesizer. The 6.5-45.5 GHz ultra-wide cryogenic receiver could be suitable for applications either main focus or second focus of the parabolic antenna. The receiver will provide a new observation window for the large scale single dish telescopes and array which are working at centimeter wavelength. The multi-band simultaneous observation data will provide opportunities for more scientific discoveries.

致冷接收机是射电天文望远镜的核心观测设备，更低的噪声和更宽的观测频带是接收机技术一直追寻的两大发展目标。本项目首次提出研究覆盖厘米波段至长毫米波波段的超宽带致冷接收机，频率范围6.5-45.5GHz，包含C/X/Ku/K/Ka/Q共计六个射电天文波段，含馈源在内的接收机整体噪声温度低于40K，可以开展超过30条重要天文谱线观测、超过30GHz带宽天文连续谱观测、实现C/K/Q和X/Ka等灵活的多波段组合观测。本项目将针对四项关键技术开展研究，超宽带馈源和极化器为核心的无源器件研究、超宽带致冷MMIC低噪声放大器为核心的有源器件研究、大口径低损耗微波窗口为核心的整体致冷技术研究、高镜像抑制和宽带频率合成为核心的超宽带变频技术研究。6.5-45.5GHz超宽带致冷接收机适用于主焦和卡焦类型的抛物面天线，将为厘米波段射电望远镜及其阵列提供全新的观测视角，多波段同时观测数据将支撑未知的科学发现。

致冷接收机是射电天文望远镜的核心观测设备，更低的噪声和更宽的观测频带是接收机技术一直追寻的两大发展目标。本项目完成了任务书规定的针对6.5-45.5GHz超宽带致冷接收机的相关研究内容，重要成果和关键数据有：超宽带馈源与极化网络研究方面，完成了两款样件研制，一款是针对主焦和环焦天线应用的入射角半角65度的6.5-45.5GHz超宽带馈源和极化网络，实测输出回波损耗好于-10dB，极化隔离度好于30dB，第二款是针对65米口径天马望远镜卡塞格伦焦点应用的入射角半角13度的4-16GHz超宽带馈源和极化网络，天线联合仿真获得全频带60%以上口径效率，实测回波损耗好于-15dB，极化隔离度好于-30dB；MMIC形式的低噪声放大器芯片以及下变频器芯片研究方面，使用台湾WIN 150nm GaAs pHMET工艺成功研制了一款6.5-45.5GHz低噪声放大器芯片，并完成了封装测试，芯片增益平坦并且大于20dB，输入回波损耗好于-10dB，输出回波损耗好于-15dB，无条件稳定，常温实测噪声温度在550K，同时研发了6.5-30GHz和30-50GHz两款SOC（System On Chip）变频芯片，实测转换增益均大于0dB；超宽带低损耗微波窗口研究方面，完成了3-18GHz、18-26.5GHz、以及26-40GHz三款窗口样件设计，基本实现了6.5-45.5GHz的频率覆盖，最大口径达到220mm，实测杜瓦真空度在低温环境下达到1E‐8 mbar量级，窗口插损对于接收机噪声贡献小于3K。在本项目研究过程中，发表相关科技文章8篇，培养研究生6名，协办一次国内技术研讨会。本项目研究成果将为国内大口径射电望远镜研发高频段超宽带接收系统提供借鉴，使得多波段同时连续观测成为可能，相关成果在深空探测多频同时观测以及超宽带军事侦察都具有应用前景。