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Paper: Full-Sampling Focal Plane Arrays
Volume: 217, Imaging at Radio Through Submillimeter Wavelengths
Page: 11
Authors: Fisher, J. R.; Bradley, R. F.
Abstract: The efficiency 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 being able to correct for large scale reflector distortions and off-axis gain loss. 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 amplifiers to reduce the uncooled prototype array noise temperature to about 50K. This will allow us to compare measured spillover and efficiency with our calculated values. The high frequency bandwidth limit is determined by the element spacing, which must be no greater than about 0.65 to 0.9 λ, depending on reflector F/D. The low frequency limit is determined by the degree to which mutual coupling can be accounted for. Our prototype takes a conservative approach with spacing > 0.5λ where measure coupling is less than -15 dB. Computed pattern distortions for the embedded element are modest.
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