Synthetic-Aperture Radar Based on Nonsinusoidal Functions: VI-Pulse-Position and Pulse-Shape Coding

Abstract

Previous papers of this series have used coded radio signals with desirable features, without explaining how these signals were obtained. This paper supplies the explanation. The concept of coding is generalized from the baseband signals, modulated onto sinusoidal carriers, to the radio signals actually transmitted. The conventional radar signals have coded baseband signals, which are referred to as the fine structure of the radar signals, while the carrier, referred to as the hyperfine structure, has always sinusoidal time variation. The more general radio signals discussed here have both a coded fine structure and hyperfine structure. Two classic problems of radar are readily solved by this generalized coding. 1) A class of signals is derived that approaches the ideal thumbtack ambiguity function in the range-Doppler domain as closely as one wants to. 2) The same class of signals makes it possible to increase the average-to- peak power ratio significantly over that achievable with frequency- modulated sinusoidal carriers. An estimate of the number of terms of a Fourier-series expansion of the signals, as well as the number of components of each term, is given; this estimate shows that a Fourier representation is too complicated for practical purposes, but also that the signals are ideal for frequency-sharing and spread-spectrum transmission.