Researchers applied theoretical models acquired from the fractal antenna research community to model the antenna characteristics of the UAV swarm configurations represented in Figures 3a and 3b.² Figure 4 (see page 38) depicts an approximate gain-versus-frequency plot that demonstrates the multiband nature of this delta (triangular-shaped) wing UAV’s conformal antenna array configuration. The solid curve shown in Figure 4 represents the multiband frequency response of the sample, three- UAV, long-range swarm configuration illustrated in Figure 3a, whereas the dotted curve represents the multiband frequency response of the sample, three- UAV, close-range swarm configuration of Figure 3b. The sample long-range configuration indicates good multiband frequency response, in the respective neighborhood of 1 GHz, 2 GHz, and 4 GHz for each of the three sample UAVs. The close-range configuration indicates good multiband frequency response as well, again in the vicinity of 1 GHz, 2 GHz, and 4 GHz.

Researchers can use a number of multiband aperture geometric constructs (e.g., Cantor Set, Sierpinski Carpet) of simple repeating and self-similar linear antenna arrays for collapsing and closing UAV swarms. They can design these linear arrays to expand in real time during the UAV swarm’s collapse phase to form multiband arrays that include lowfrequency bands. These expanding lowfrequency arrays can adaptively inspect buildings for signal leakage points during outdoor-to-indoor inspection for objects of interest inside buildings.

Figure 5 illustrates a concept wherein a relatively large hovercraft is equipped with legs that function as RF apertures. In this concept, each leg contains smaller hovercrafts that function as antenna array elements. When the larger hovercraft detects a region of interest, it ejects the smaller hovercrafts from the legs, thereby expanding and forming large, multiband, linear fractal arrays to gather information regarding movement within buildings, building contents, and other electromagnetic penetrable surfaces. The small hovercraft can adapt their positions to obtain signal leakage points as a function of frequency and position. As an example, the large hovercraft can transmit signals at different frequencies, and the smaller hovercraft elements can receive the scattered radar signals and transmit the signals to the larger hovercraft for processing and transmission to a remote ground station. Researchers can formulate many other variations of these sample configurations to develop collapsing and closing UAV swarm systems using multiband linear fractal arrays.

Researchers are exploring additional future applications that include joint RF and electro-optical (EO) sensors applications for collapsing and closing UAV swarms. For example, they could develop configurations in which the full swarm forms an RF aperture and some of the collapsing swarms use near-range EO video camera, laser, or infrared technologies.

Dr. Atindra K. Mitra, of the Air Force Research Laboratory’s Sensors Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn_index.asp. Reference document SN-H-05-02.

References

¹ Mitra, A. “Position-Adaptive Unmanned Air Vehicle Radar.” AFRL Technology Horizons®, vol 5, no 6 (Dec 04): 24. http://www.afrlhorizons.com/Briefs/Dec04/S N0403.html.
² Gingrich, M. A., Werner, D. H., and Werner, P. L. “A Self-Similar Fractal Radiation Pattern Synthesis Technique for Reconfigurable Multiband Arrays.” IEEE Transactions on Antennas and Propagation, Jul 03.