A 230 GHz focal plane array using a wide IF bandwidth SIS receiver
A 230 GHz focal plane array using a wide IF bandwidth SIS receiver
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使用宽 IF 带宽 SIS 接收器的 230 GHz 焦平面阵列
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发表时间：
2018
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通讯作者：
J. Garrett
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作者：
J. Garrett
超导体-绝缘体-超导体（SIS）混频器在毫米波下提供了所有外差混频器技术中最好的噪声特性。在天文学中，它们被用于敏感光谱学，这对于理解冷星际介质的特性至关重要，包括恒星形成活动区域。现代SIS接收器的噪声特性是量子极限的T3倍，现在进一步降低噪声特性变得越来越困难。在本文中，我研究了两种扩展SIS接收器能力的技术。第一种技术是扩展接收机的瞬时带宽，即中频带宽（IFBW）。对于光谱线源，宽IFBW扩展了调查深度，允许同时观测多个发射线。在这里，我提出了一个新的230 GHz的SIS混频器设备。平面电路被最小化，以减少任何可能限制IFBW的寄生电容。在实验中，该器件提供了极好的噪声温度，低至36 K， IFBW范围约为0-11 GHz。为了更好地了解该器件的性能，开发了仿真软件，并表明如果升级中频测量链，IFBW可以扩展到更高的频率。我研究的第二种技术是增加接收器焦平面上的接收器数量，即增加更多的像素。这项任务涉及许多挑战，包括如何将多个接收器安装在一个小空间中，如何适当地冷却接收器，以及如何传递本地振荡器信号。在这里，我提出了一个新的1 × 4焦平面阵列。这个阵列作为一个新的阵列架构的演示，可以在未来扩展到更多的像素。利用级联波导功率分配器对本振信号进行分频，再用波导定向耦合器将本振信号与天文信号结合。最后，我介绍了5muse巡天中34个星系的CO（J=1→0）测量结果。这些测量追踪了这些星系中存在的冷分子气体的数量。通过将这些测量结果与追踪恒星形成活动的其他指标（例如，红外光度）进行比较，我能够在观察到的数量之间形成经验关系。我还将这些结果与附近和高红移星系的其他恒星形成研究结合起来，形成了跨越宇宙时间很大一部分的尺度关系。
Superconductor-Insulator-Superconductor (SIS) mixers offer the best noise properties of any heterodyne mixing technique at millimetre wavelengths. In astronomy, they are used for sensitive spectroscopy, which is vital for understanding the properties of the cold interstellar medium, including regions of star formation activity. Modern SIS receivers have noise properties that are T3 times the quantum limit, and it is now becoming increasingly difficult to lower the noise properties any further. In this thesis, I investigate two techniques that extend the capability of SIS receivers. The first technique is extending the instantaneous bandwidth of the receivers, i.e., the intermediate frequency bandwidth (IFBW). For spectral line sources, wide IFBW expands the survey depth to allow multiple emission lines to be observed simultaneously. Here, I present a new SIS mixer device at 230 GHz. The planar circuit was minimised to reduce any parasitic capacitances that may limit the IFBW. Experimentally, the device provides excellent noise temperatures down to 36 K and an IFBW extending from approximately 0–11 GHz. Simulation software was developed to better understand the performance of this device, and it suggests that the IFBW can be extended to higher frequencies if the IF measurement chain is upgraded. The second technique that I investigate is increasing the number of receivers in the focal plane of the receiver, i.e., adding more pixels. There are many challenges involved in this task including how to fit multiple receivers into a small space, how to properly cool the receiver, and how to deliver the local-oscillator signal. Here, I present a new 1 × 4 focal plane array. This array is acting as a demonstrator for a new array architecture that can be expanded into many more pixels in the future. It uses cascaded waveguide power splitters to divide the local-oscillator signal, and then waveguide directional couplers to combine the LO with the astronomical signals. Finally, I present CO(J=1→0) measurements from 34 galaxies in the 5MUSES survey. These measurements trace the amount of cold molecular gas present in these galaxies. By comparing these measurements to other metrics that trace star formation activity (e.g., infrared luminosity), I was able to form empirical relationships between the observed quantities. I also combined these results with other star formation studies from nearby and high redshift galaxies to form scaling relationships spanning a large fraction of cosmic time.