We report a novel technique for microwave imaging utilizing a nonlinear coupling between the microwave fields in a ferromagnetic material, in which the relative phase of the coupled microwave fields plays an important role in the resultant homodyne dc voltage. A technical breakthrough has been achieved to effectively control such a relative phase using a spintronic Michelson interferometry. This enables a phase- and amplitude-resolved near-field dielectric image using a spintronic sensor. The contrast of microwave imaging for an object with subwavelength features strongly depends on the local dielectric constant of materials, and agrees well with simulation results by COMSOL.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.