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ISAR imaging via discrete multitone transmit and channelized narrowband receive processing

By transmitting and receiving several discrete tones, a tactical Navy radar can image a target via ISAR with little EMI on surrounding radar systems. Standard methods of stepped frequency sequentially transmit single frequency information which has the striking drawback of large amounts of contiguous transmit time. For large bandwidths and maneuvering targets, requiring several hundreds of milliseconds per frequency set could produce range smearing. FM-CW has the drawback that again, (in tactical environment) occupying several hundred MHz of contiguous bandwidth could interfere with other uses of the band. The method of ISAR image formation that will be described here utilizes a transmit waveform comprising a discrete set of tones. This waveform has many advantages over waveforms that require tactically significant amounts of either time or bandwidth. The specific system that will be discussed will be an augmented x-band CW tracking radar. A method of selecting the specific frequencies will be discussed along with a method of pairwise mixing the receive tones, known as Delta-K, that can be utilized for range profile sidelobe reduction. A method of calibrating the phase differences between channels will be discussed in detail. Results from simulations and data from a real system will be discussed.