CubeSounder: Low SWaP-C 180 GHz Radiometer for Atmospheric Sensing Tested on High Altitude Balloons

Abstract

Microwave sounding is the leading driver of global numerical weather forecasting, but is limited by the scalability of such instruments. With modern machining and commercial microwave components, it is now possible to design low size, weight, power, and cost (SWaP-C) microwave spectrometers while maintaining wide bandwidth performance. Here we report on the status of CubeSounder, a spectrometer tailored for water vapor radiometry that utilizes passive wave guide filter banks. After developing a prototype and high altitude balloon payload, we demonstrated CubeSounder on commercial stratospheric balloon flights. We report on our design process, especially the simulation and fabrication of the custom millimeter-wave filter banks. We also report the initial results of the data collected from the balloon flights.

Figures (11)

• Figure 1: Drawing of spectrometer system. Broadband signal enters the feed horn, is then amplified by LNAs and finally divided by filter-bank. The filter-bank is a passive component of directly milled metal based on a novel design.
• Figure 2: An example of the waveguide filter-bank concept. Broadband light propagates through the waveguide and different frequency bands are selected off of the main waveguide by the five channels. Center frequency of each channel is defined by length of resonant cavity.
• Figure 3: Results from our end-to-end filter bank design and simulation software. Each channel is constructed in CST studio individually then the S-matrices are cascaded with a Python script. Figure shows the predicted through power of the V-band filter bank.
• Figure 4: An aluminum machined split block half from the V-band prototype filter bank. Waveguide sections were milled to half the depth of a standard WR-15 rectangular waveguide. When mated to the other half of split block, the cavity will be the standard waveguide size. Resonant cavity filters split off of main thru channel. Screw and dowel holes are included for split block mating and alignment. This block was machined by Xometry
• Figure 5: The CubeSounder electronics boards which handles readout, storage of sensor data, DC power conversion, as well as the running of accessories such as the real time clock and tiltmeter.