Beam Propagation Model Selection for Millimeter-Wave Directed Energy Weapons

Comparing the relatively simple Fraunhofer or “far field” (FF) approximation commonly used in radar and high-powered microwave systems with the more complex near field (NF) propagation model based on the field equivalence principle demonstrates which approach achieves reasonable modeling fidelity with minimal compute power.

Institute for Defense Analyses, Alexandria, Virginia

Modeling and Simulation (M&S) can be used to explore the design trade space of directed energy weapons. M&S can be particularly helpful when that trade space is influenced by a large number of parameters and when acquiring field data to explore those parameters requires a large amount of resources. One example involves the Active Denial Technology (ADT) system, a non-lethal, counter-personnel, directed energy weapon that outputs high-powered, millimeter wave electromagnetic energy for crowd control, patrol/convoy protection, and perimeter security. The accompanying figure shows a photograph of a current ADT demonstrator (left) and a conceptual drawing of a future iteration of ADT (right).

The ADT system subjects a targeted individual to short-duration pulses of a focused beam of directed energy operating at a frequency of approximately 95 GHz (3.2 millimeters in wavelength). At this frequency, and within a known range of doses, the energy diffuses approximately 1/64th inch (400 microns) into the skin of the targeted individual, producing no skin damage. Yet the targeted individual perceives an intense burning sensation, potentially strong enough to repel-that is, to compel the targeted individual to immediately flee the beam.