Beam Propagation Model Selection for Millimeter-Wave Directed Energy Weapons (Presentation)
INSTITUTE FOR DEFENSE ANALYSES ALEXANDRIA VA ALEXANDRIA United States
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We consider low complexity beam propagation models of high powered, millimeter wave 95 GHz systems. The goal is to achievereasonable modeling fidelity with minimal compute power, allowing for rapid sampling in large parametric trade space studies. One modelunder consideration is the relatively simple Fraunhofer e.g. far field approximation which is commonly used in radar and high poweredmicrowave systems. However at the frequency of interest, operational ranges for these systems can fall within the Fresnel zone where theassumptions of the Fraunhofer approximation are violated. As such we also construct a near field propagation model based on the fieldequivalence principle. This model is necessarily more complex than the Fraunhofer approximation, but is considerably less compute-intensivethan full-wave solutions. We compare incident power estimates from the near field and Fraunhofer models for fixed focus andvariable focus millimeter wave systems, showing that the models disagree primarily at ranges below the focal range as expected. Hencein this regime, we expect that the near field model to be the most appropriate. At the focal range and beyond, the models give similarresults, suggesting that the Fraunhofer approximation may be sufficient for characterizing incident power near the focal point, even withinthe Fresnel zone.