Three Dimensional Holographic Microwave Imaging using Feko
The concept of Holographic based imaging was originally adopted in the field of optical imaging. Modern holographic concepts have proved to be most promising techniques for three dimensional microwave and millimeter wave imaging. These holographic microwave imaging (MWI) techniques can provide qualitative images for the media in inspection. In near-field holographic MWI approach, either a prior knowledge of incident field and Green's function for the antennas are used or the measured point spread function (PSF) are employed. In direct MWI, wideband data is required to obtain range resolution. The 3D image is reconstructed as a set of 2D image slices captured at various depths. The figure below is an illustration of a wideband 3D microwave holographic imaging setup that consists of a transmitter antenna and a receiver antenna that move together to scan a rectangular aperture.
Although the above mentioned technique is fast and robust, there are some drawbacks associated with it. Since the data is collected for a very wideband, the data acquisition system that includes antennas and other circuitry can be complex. Implementing low cost data acquisition techniques can be challenging and inefficient for wideband systems. Additional errors can be imposed on reconstructed images due to dispersive properties of media under inspection.
The first paper attached with this article demonstrates the feasibility of achieving range resolution with single frequency microwave data with 2D results. An array of resonant antennas are used to receive backscattered data in Altair Feko. The data can then be processed with holographic image reconstruction algorithm in a tool like Altair Compose. After achieving satisfactory results the proposed approach was extended to 3D imaging. Simulations were conducted to study various parameters like number of antennas, number of reconstruction lines, distance between the planes, and effect of noise. The simulation data was contaminated by noise to perform a realistic study. The extended study is published in the second paper attached with this article. All simulations were conducted in Altair Feko. The illustration of the above approach is provided in the figure below. The setup contains one transmitting antenna that Illuminates the media with microwave power and N receiving antennas.
The figures below show two setups in Altair Feko used for demonstrating 3D imaging.
The figure below displays the 3D imaging results for the examples shown above. The objects can be clearly observed in the reconstructed images.
All the dimensions and material information are provided in the paper so that a reader can repeat the work. Using single frequency data in the proposed technique allows for employing data acquisition techniques such as modulated scatterer technique (MST) or employing resonant antennas or probes which are more sensitive, for example, in microwave or millimeter wave microscopy applications. Other Applications can include security screening, underground imaging, wall imaging and many more.
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