Near field microwave imaging is based on transmitting a wave into a dielectric structure, which is located in the near field of a sensor, and using a signal proportional to the magnitude and/or phase of the transmitted or reflected wave to create a two or three dimensional image of the structure under investigation. To analyze the features and properties of an image, it is important to understand the mechanism by which the incident electric and magnetic fields interact with the structure. In this study, an effective dielectric constant formula is used to model the reflection properties of two and three dielectric half spaces arranged side by side when scanned by on open ended rectangular waveguide probe. Importantly, the influence of the nonuniformity associated with the electric field distribution at the waveguide aperture is investigated as well. To this end, linear and nonlinear volume fraction calculations are incorporated to calculate the effective dielectric constant of the specimens made of two and three dielectric half spaces. Consequently, the phase and magnitude of the reflection coefficient at the waveguide aperture are calculated. Theoretical and experimental results are presented and compared. In addition, a discussion related to the relative influences of the effective dielectric constant and aperture field distribution is presented
