A 3-D microwave holographic imaging algorithm compatible with reflection-coefficient measurement setup is proposed. It can be divided into four parts. First, starting from the open-circuit voltage of antenna, the algorithm compensates for both transmitting and receiving properties of the probe antenna, leading to antenna-independent least squares problems. However, the problems tend to be ill-conditioned. An auxiliary equation is thus derived and exploited to effectively improve the numerical stability and image quality. Third, to accurately locate the unknown target in range direction, a phase compensation method that requires only phase correction to the associated entries of the kernel matrix is proposed based on a simple ray model. Last, considering the finite size of the scanning aperture and beamwidth of the probe antenna, a numerical low-pass filter in the spatial-frequency domain is utilized to effectively locate the worth-solving area. For verification, a series of images reconstructed from the simulated and measured data using the proposed algorithm are presented. Thanks to the enhanced image quality, the geometry, location, and dielectric constant of the target can be retrieved. The range and cross-range resolutions achieved are about λ 10 and λ/4, respectively.
- near-field microwave imaging
- probe compensation