An electronic support measures (ESM) system, intercepts and measures radar signal parameters, in order to provide signal identification and threat analysis. The paper presents a novel acousto-optic (AO) technique, which allows for the processing of received radar signals in the optical domain. It uses an innovative design of AO cell combined with polychromatic optical illumination. Essentially, the technique upshifts the radar signal to the optical band, producing an optical beam with a linear mapping between radio frequency and optical frequency. It is then possible to perform further processing of the radar signal by manipulating the optical signal; an elementary example would be optical spectral analysis, providing frequency information on the intercepted radar signal. The theory of operation of the technique is outlined, the time bandwidth product is derived and the coherence properties of the optical signal are discussed. Some of the processing options available are described, including the possibility of increased frequency resolution.
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