180-GHz Interferometric Imager
- Created: Tuesday, 01 November 2011
A 180-GHz interferometric imager uses compact receiver modules, combined high- and low-gain antennas, and ASIC (application specific integrated circuit) correlator technology, enabling continuous, all-weather observations of water vapor with 25-km resolution and 0.3-K noise in 15 minutes of observation for numerical weather forecasting and tropical storm prediction.
The GeoSTAR-II prototype instrument
is broken down into four major
subsystems: the compact, low-noise
receivers; sub-array modules; IF signal
distribution; and the digitizer/correlator.
Instead of the single row of antennas
adopted in GeoSTAR, this version has
four rows of antennas on a coarser grid.
This dramatically improves the sensitivity
in the desired field of view.
The GeoSTAR-II instrument is a 48- element, synthetic, thinned aperture radiometer operating at 165–183 GHz. The instrument has compact receivers integrated into “tiles” of 16 elements in a 4×4 arrangement. These tiles become the building block of larger arrays. The tiles contain signal distribution for bias controls, IF signal, and local oscillator signals. The IF signals are digitized and correlated using an ASIC correlator to minimize power consumption.
Previous synthetic aperture imagers have used comparatively large multichip modules, whereas this approach uses chip-scale modules mounted on circuit boards, which are in turn mounted on the distribution manifolds. This minimizes the number of connectors and reduces system mass. The use of ASIC technology in the digitizers and correlators leads to a power reduction close to an order of magnitude.