Signal and Data-Processing Antennas

This paper treats the antenna as an information processing device, and applies the concepts of modern information theory to the design of antennas and to the optimization of their performance. The principal optimization criterion employed is maximization of information or data rate. The general procedure is to treat the antenna as a spatial frequency filter which is being optimized subject to a given set of control inputs. Given these specifications, the information rate is maximized with respect to the antenna system parameters subject to the physical constraints of the system. It is shown that in a general antenna system where noise is introduced in both the object and image space, the optimum antenna aperture distribution is uniform. When the image, or receiver, noise is zero, the useful output information content and rate are independent of the aperture distribution. An equation relating the signal and noise spectra and the aperture distribution is derived which shows the way in which the signal should be coded so as to maximize the information content. Processing is discussed generally, and a specific nonlinear processing scheme is analyzed. The general conclusion is that nonlinear processing degrades the useful information rate when the SNR is low whereas it may improve the rate at high SNRs. Finally, a number of specific military and space applications of information processing antennas are considered.