ABSTRACT:In this paper, we apply microwave holography to infrared (IR) thermal images of electromagnetic (EM) fields to measure near-field and far-field radiation patterns of antennas. The phase of the field is retrieved from IR thermograms (magnitude-only thermal images of the field) measured in the near field of the antenna using microwave holography. One method to extract the phase is to use an iterative plane-to-plane (PTP) two-dimensional (2D) holographic phase retrieval method. After the phase is recovered, the near-field thermographic/holographic data can be processed to determine the complex intensity (magnitude and phase) of the field at any distance in front of the antenna under test (AUT). Of particular interest is the far-field radiation pattern of the antenna or, especially for phased array antennas, the aperture source-plane distribution. Numerical simulations were performed to determine the feasibility, accuracy, and sensitivity of these IR thermographic/holographic phase-retrieval techniques. The advantages and disadvantages of the technique are also discussed. To demonstrate the feasibility of the technique, actual IR thermograms were obtained at the Air Force Research Laboratory/ Rome Research Site (AFRL/RRS) in Rome, (New York) and holograms were derived from a simple planar 6 ϫ 6 phased array patch antenna using the PTP technique. The phase-retrieval results are presented and compared with the known results for this antenna, as measured on the near-field range at the National Institute of Technology and Standards (NIST) using standard hard-wired probes. The agreement between the results for this antenna is very good.

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The paper presents results which demonstrate that radiated emissions from heatsinks are reduced by an amount that depends upon the distribution and impedance of the grounding structure. Results are also presented which show the effect on radiated emissions of the presence of conductors (e.g. PCB tracks) passing under the heatsink. The presence of conductors reduces the effectiveness of the heatsink grounding but, in most case, emissions at high frequencies do not exceed those without conductors attached.

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