A type of reflectarray antenna now undergoing development is based on the concept of a reflector membrane that is stretched flat by attaching it to an inflatable frame (see figure). Antennas of this type are meant to serve as lightweight, compactly stowable, reliable alternatives to conventional antennas with rigid reflector structures or mechanically deployed mesh reflectors. Originally intended for use aboard spacecraft for microwave communications, these antennas might also prove useful in terrestrial low-power, lightweight microwave systems in cases in which reflector-surface distortions caused by gravitation and wind could be tolerated.
The reflectarray in an antenna of this type is a planar array of microstrip patches printed on a thin circular membrane. An inflatable circular toroidal tube is attached to the edge of the membrane; when inflated, the tube stretches the membrane flat and supports the membrane in the operational configuration. Inflatable tripod tubes attached to the inflatable torus serve as struts to support a feed horn that illuminates the reflectarray. The patches of the reflectarray are shaped and sized to make the reflected electromagnetic field cophasal, so that the antenna operates with high gain.
It must be emphasized that surface of an antenna of this type is designed to be flat - in contradistinction to the paraboloidal shape of a conventional antenna reflector. In a previous attempt to deploy an inflatable antenna with a paraboloidal reflector surface, the surface figure deviated from the required paraboloid by far more than the maximum allowable error. In the present case, achievement of the desired precision in the surface figure is not difficult; the desired flatness is readily maintained by stretching the membrane.
A prototype with an overall size of about 1 m, designed for operation in the X band, has been built and tested. The inflatable antenna structure should be mass-producible at low cost.
This work was done by John Huang and Alfonso Feria of Caltech for NASA's Jet Propulsion Laboratory. NPO-20433
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Inflatable reflectarray antennas
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