Timed arrays and their application to impulse SAR for "through-the-wall" imaging

This paper is intended to present a simple description of operation and performance of timed arrays, i.e., arrays that operate in the transient regime. The arrays can be real and/or synthetic, although the latter are of prevailing interest for this paper. This paper presents, in the simplest possible way, the physics of radiation and reception in transient operations, and the properly accommodated transmission and reception parameters of the antenna. The striking result is that the new parameters are very similar, if not identical, to their steady state counterpart, provided that the wavelength (steady state case) is substituted by the radiated pulse spatial width (transient operations). We also discuss the necessary procedure to radiate pulses, and its impact in terms of a reduced antenna efficiency: the gain of the antenna is much smaller than its directivity. The timed arrays are discussed and their aperture angle is explicitly computed, so that the resolution of the synthetic array can be evaluated: its expression turns out to be formally coincident with its steady state counterpart. Preliminary considerations about the impulse SAR processing are discussed.