Digital false-target image synthesiser for countering ISAR

The paper presents the design of a pipelined, all-digital image synthesiser capable of generating false-target images from a series of intercepted inverse synthetic aperture radar (ISAR) chirp pulses to provide a novel RF imaging decoy capability. The image synthesiser modulates the phase samples from a phase-sampling digital RF memory (DRFM) that stores intercepted ISAR pulses. The synthesiser contains a parallel array of (identical) complex digital modulators with one modulator for each false-target range bin. The binary phase samples from each intercepted ISAR pulse are applied one at a time to the modulator array. To synthesise the image, each modulator requires a set of phase and gain coefficients that are derived from the range-Doppler description of the false-target to be synthesised. An ISAR image compression algorithm is presented to reconstruct the image using the synthesiser output pulses. A ship with 32 range bins is presented as an example of a false-target input, and simulations are used to quantify the image synthesis capability of the architecture. The image quality as a function of the number of ISAR pulses integrated is also numerically evaluated. The programmable design permits real-time alteration of modulation coefficients, allowing rapid and adaptive shifting among different types of targets offering a low-cost decoy capability using readily available DRFM technology.