Multispectral RF Imaging Using Multiple Narrow-Band FMCW Signals

Although there are commercial platforms with large antenna arrays operating over wide bands, narrow-band signals remain favored due to the hardware complexity and maximum unambiguous range considerations. This paper introduces a radio frequency (RF) imaging method employing multiple narrow-band frequency-modulated continuous wave (MNB-FMCW) signals to cover a wide band. Tailored for this design, a wide-band channel model is developed in which the channel response is assumed to be flat within each narrow band but varies across different bands. This produces diverse images capturing both range and direction-of-arrival information from different bands, leading to multispectral imaging. A computationally efficient algorithm is then devised by leveraging the conjugate gradient method and fast Fourier transform. Simulations based on practical parameters demonstrate that the proposed design produces multispectral RF images, and synthesizes more angular pixels than antennas in a uniform linear array.