In this paper, a wavenumber-domain matrix-pencilbased multiband signal fusion approach was proposed for multiband microwave imaging. The approach proposed is based on the Born approximation of the field scattered from a target resulting in the fact that in a given scattering direction, the scattered field can be represented over the whole frequency band as a sum of the same number of contributions. Exploiting the measured multiband data and taking advantage of the parametric modeling for the signals in a radial direction, a unified signal model can be estimated for a large bandwidth in the wavenumber domain. It can be used to fuse the signals at different subbands by extrapolating the missing data in the frequency gaps between them or coherently integrating the overlaps between the adjacent subbands, thus synthesizing an equivalent wideband signal spectrum. Taking an inverse Fourier transform, the synthesized spectrum results in a focused image with improved resolution. Compared with the space-time domain fusion methods, the proposed approach is applicable for radar imaging with the signals collected by either collocated or noncollocated arrays in different frequency bands. Its effectiveness and accuracy are demonstrated through both numerical simulations and experimental imaging results.Index Terms-Matrix-pencil approach (MPA), microwave imaging, multiband signal, signal fusion, wavenumber domain.
I. INTRODUCTIONM ICROWAVE imaging has been widely used for nondestructive testing, security check, medical imaging, remote sensing, and so on. In these applications, imaging radar systems generally exploit wideband signals and antenna arrays to achieve high resolution in both downrange and cross-range directions. As downrange resolution is inversely proportional to the operational signal bandwidth of the imaging system, signals with several gigahertz or even larger bandwidth are required to achieve cm/sub-cm level resolutions, especially for short-range applications. To emit and receive such wideband signals, ultrawideband (UWB) antennas and front ends are needed. Vector network analyzers (VNAs)