Full-Sampling Focal Plane Arrays

The eeciency of single dish mapping and synthesis array mosaicing can be increased by completely sampling the information in the antenna's focal plane. This requires a densely packed array of electrically small elements. Each telescope beam is formed with a weighted combination of signals from seven or more elements. This has the added advantage of correcting for large scale reeector distortions and oo-axis gain loss. The high frequency bandwidth limit is determined by the element spacing, which must be no greater than about 0.65 to 0.9, depending on reeector F/D. The low frequency limit is determined by the degree to which mutual coupling can be included in the design. We have demonstrated the feasibility of forming closely spaced beams with a low-sensitivity, 1.4 GHz, 19-element array. We will show some initial results. The array elements are now being integrated with balanced HFET ampliiers to reduce the uncooled prototype array noise temperature to about 50K. This will allow us to compare measured spillover and eeciency with our calculated values.