On the use of antenna engineering tools for the optimization of the focal plane sampling in direct detection of distributed sources

The design of focal planes of direct detectors for the characterization of radiometric distributed sources in the sub-mm wave regime is a problem of renewed interest for the scientific community. The important question is how to optimize the focal plane sampling or the focal plane feed elements for maximizing the acquisition speed. The key speed limitations for some popular feed solutions have been qualitatively discussed in the optical scientific literature. The presented solutions were dominated only by the photon and detector noise. However, the actual realistic estimation of the acquisition speeds is complicated when rigorous electromagnetic calculations have to be performed. While, the basic estimations are supposedly well understood in the scientific astronomical communities, the realistic estimation requires the tools typical of antenna engineers. This is particularly important when the bandwidth of the desired systems is large. This paper tries to address some key difficulties, from a rigorous electromagnetic point of view, which seem to be clouding the discussions on optimal sampling.