A unique design methodology for advanced sensor design applications

AFRL researchers are exploring an adaptive and reconfigurable unmanned air vehicle (UAV) swarm configuration known as “collapsing and closing UAV swarms.” This approach to developing UAV swarms is suitable for a number of multifunction radio frequency (RF) applications in challenging environments such as urban and mountainous regions. Figures 1a-1c illustrate the basic approach. In Figure 1a, a long-range search UAV swarm collectively forms a scanning RF aperture. The swarm’s scanning RF aperture interrogates a region of interest to detect high-clutter, discrete objects such as buildings or mountains. As depicted in Figure 1b, once the swarm detects these large, obscuring objects, it “collapses and closes” in on the region between the objects. This allows the swarm configuration to interrogate the embedded channels between the buildings or mountains to look for signal leakage points within these large objects, and once detected, these leakage points facilitate cavity interrogation.¹ After the swarm has finished interrogating the embedded channels and cavities, it reconfigures itself for RF long-range remote sensing with regard to the next region of interest, as illustrated by Figure 1c.

One approach to designing an RF antenna array for this application is to use the fractal geometrical construct of the Sierpinski Gasket. In constructing the gasket, scientists start with an equilateral triangle, S₍₀₎, subsequently dividing it into four smaller equilateral triangles using the midpoint of each of the original triangle’s three sides (see Figure 2). They next remove the middle triangle, leaving the solid surfaces of the three remaining triangles, to obtain S₍₁₎. Repeating this procedure for each of the three remaining solid equilateral triangles results in S₍₂₎, and repeating it once more produces S₍₃₎.

Researchers chose to evaluate the antenna performance of the S₍₃₎ configuration for long-endurance search (see Figure 3a on page 38). The black triangles represent integrated fractal antenna elements. When the swarm detects large target areas of interest, it collapses by separating into three distinct UAVs (see Figure 3b on page 38) and closes in on the area of interest to individually interrogate leakage points. Upon completing the interrogation, the UAVs regroup into the original configuration for continued longendurance search activities.