A One-Dimensional Synthetic-Aperture Microwave Radiometer

Goddard Space Flight Center, Greenbelt, Maryland

A proposed one-dimensional synthetic-aperture microwave radiometer could serve as an alternative to either the two-dimensional synthetic-aperture radiometer described in the immediately preceding article or to a prior one-dimensional one, denoted the Electrically Scanned Thinned Array Radiometer (ESTAR), mentioned in that article. The proposed radiometer would operate in a “pushbroom” imaging mode, utilizing (1) interferometric cross-track scanning to obtain cross-track resolution and (2) the focusing property of a reflector for along-track resolution.

The Antenna of the Proposed Radiometer would consist of microwave feed horns positioned alongthe focal line of a cylindrical parabolic reflector. In one potential application, there would be two setsof feed horns for operation at two frequencies: the larger ones would be 18.7 GHz, the smaller onesfor 37.0 GHz.

The most novel aspect of the proposed system would be the antenna (see figure), which would include a cylindrical reflector of offset parabolic cross section. The reflector could be made of a lightweight, flexible material amenable to stowage and deployment. Other than a stowage/deployment mechanism, the antenna would not include moving parts, and cross-track scanning would not entail mechanical rotation of the antenna. During operation, the focal line, parallel to the cylindrical axis, would be oriented in the cross-track direction, so that placement of receiving/ radiating elements at the focal line would afford the desired along-track resolution.

The elements would be microwave feed horns sparsely arrayed along the focal line. The feed horns would be oriented with their short and long cross-sectional dimensions parallel and perpendicular, respectively, to the cylindrical axis to obtain fanshaped beams having their broad and narrow cross-sectional dimensions parallel and perpendicular, respectively, to the cylindrical axis. The interference among the beams would be controlled in the same manner as in the ESTAR to obtain along-cylindrical-axis (cross-track) resolution and cross-track scanning.

This work was done by Terence Doiron and Jeffrey Piepmeier of Goddard Space Flight Center. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. GSC-14748-1