A lightweight reflectarray antenna that would enable simultaneous operation at frequencies near 7.115 GHz and frequencies near 32 GHz is undergoing development. More precisely, what is being developed is a combination of two reflectarray antennas — one for each frequency band — that share the same aperture. (A single reflectarray cannot work in both frequency bands.) The main advantage of the single dual-band reflectarray is that it would weigh less and occupy less space than do two single-band reflectarray antennas.
A reflectarray antenna consists mainly of a planar array of microstrip patches on a suitable dielectric substrate. In a prototype of the dual-band reflectarray antenna (see figure), the 7.115-GHz reflectarray antenna consists of crossed dipole microstrip patches on a thin polyimide membrane; the 32-GHz reflectarray antenna consists of square microstrip patches on top and a ground plane on the bottom of a poly (tetrafluoroethylene)/ ceramic composite substrate. The ground plane is bonded to a supporting aluminum plate. The 7.115-GHz reflectarray is placed in front, and the two reflectarrays are sandwiched together with a dielectric foam spacer between them. The crossed-dipole patches of the front (7.115-GHz) reflectarray are positioned between the square patches of the rear (32-GHz) reflectarray to minimize blockage of radiation from the rear array.
In tests of the prototype antenna, it was found that the front (7.115-GHz reflectarray) caused a 1.8-dB reduction in the 32-GHz gain, while the effect of the rear (32-GHz) reflectarray on the 7.115-GHz performance was negligible. It was also concluded, on the basis of the test data, that there is a need to refine understanding of interactions between the individual reflectarrays and to refine their designs accordingly.
This work was done by Mark Zawadzki and John Huang of Caltech for NASA's Jet Propulsion Laboratory.