In order to detect 2D underground heterogeneity between boreholes, a microwave‐imaging technique is presented along with numerical and experimental comparisons. The proposed technique is based on a spectral diffraction tomography technique which enables heterogeneities from the polarized currents induced by the incident field of a simple dipole antenna to be located. Numerical results in both a transverse‐magnetic (TM) and transverse‐electric (TE) modes are compared with a reduced‐scale physical model composed of a water tank with some immersed cylindrical heterogeneities.