The offset parabolic reflector is designed as a perimeter truss reflector. This class of reflectors offers low stowed volume and height, low mass, high surface approximation accuracy, and a wide range of apertures, from 0.5 m to 20 m and more. Strategic material selection also allows the reflector to retain its shape under the thermal cycling experienced during orbit.

The picture shows a comparison of a simulation of an ideal reflector, black lines, with an ideal mathematical approximation of the paraboloid surface, in red. The grating lobe at ~7.75 GHz is caused by the periodic nature of the surface approximation. The measured parameters were obtained by simulating the reflector with its measured geometry. All of the plots are for 100 GHz operation. As shown, the reduction of the antenna directivity is below ~-25 dB level, and thus reduces the efficiency of the main beam by less than 0.3%. BEST’s proprietary reflective surface was measured to have exceptional reflectivity up to 220 GHz.

Increased efficiency is important for radars, especially synthetic aperture radars, where the efficiency of transmitter and receiver combine. For example, for a 0.65-efficient reflector, the total efficiency (transmission and receiving) is 42%. Thus, for the synthetic aperture radar that uses a lot of power, a higher efficiency antenna can guarantee a higher duty cycle. Of course, this applies to any other radar, or communication system.

Observations of passive microwave sensors need a very efficient antenna, since only the naturally emitted noise is observed, and only the noise from the scene is desired at the sensor input.

A challenge of meteorological observations is the need to sample at the proper size and time resolution for the event/phenomena that is being observed. For example, severe weather events, such as thunderstorms, or tornadoes, require a spatial resolution on order of 10 km, and temporal resolution on the order of 10-20 minutes. Naturally, all other observations, e.g. clouds, precipitation, sea ice extension/characterization, tropical cyclone intensity, and many more would also benefit from a shorter revisit time and improved spatial resolution.

The figure from Kidd et al. shows precipitation observations from ground based radar sensors and their correlation to a passive microwave observing system with various spatial and temporal resolution parameters. For high correlation observations, the spatial resolution of the sensors, and their revisit time has to improve significantly. For example, for a conically scanning sensor operating at 650 km altitude with a ground spatial resolution of 15 km, a high level of correlation, greater than 0.9, can be achieved only with a reflector aperture size of 4.5 m at 7 GHz. The corresponding temporal resolution should be better than one hour, requiring approximately 12 sensors on orbit. At a revisit time of 0.5 hours and spatial resolution of ~5 km, severe weather events could be resolved. To achieve this, an antenna aperture at 7 GHz needs to be 13.5 m and roughly 24 sensors need to be deployed. Considering the number of sensors in these arrangements, their individual cost becomes important very quickly.