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Materials and Processes Enable New Possibilities for Unmanned Systems Command & Control

Unmanned vehicles are finding increasing usage in military engagements, not only for aerial applications but also for ground and underwater missions. Modern antenna designs can increase unmanned vehicle fuel efficiency through reduced antenna size, increased antenna conformality, and reduced antenna weight. For airborne UAVs, time on station is a critical mission parameter directly influenced by payload weight and aerodynamics. For unmanned ground vehicles, increased antenna conformality reduces the likelihood of accidental damage that occurs with externally protruding antennas.

Figure 1. Conductive coatings can be flexibly and precisely applied to composite substrates. (Source: TE Connectivity)

As designers look toward smaller and more capable UAVs, SWaP-C (size, weight, power, and cost) requirements necessitate smaller, lighter, more power-efficient components and subsystems built using modern manufacturing methods. With every subsystem as a candidate for SWaP-C improvements, small savings on subsystems can add up to significant overall savings for a platform.

Recent advances in materials and fabrication technologies are now enabling improved antenna designs with reduced size, weight, aerodynamic drag, and cost. Key innovations influencing next-generation antenna designs include composite materials and novel selective metallization processes. These innovations combine to allow cost-effective realization of three-dimensional antennas that are mechanically robust and can withstand harsh environmental conditions.

Composites

Figure 2. Moldable modular antenna design using a glass-fiber reinforced composite substrate and conductive coating. (Source: TE Connectivity)
A typical thermoplastic composite begins with high-performance engineered polymer to which fillers are added to enhance characteristics. For unmanned vehicle applications, the polymer is likely to be a high-temperature moldable thermoplastic, such as grades of PPS, PEI, or PEEK. Composite materials are strong and can be tailored to provide impact resistance, tensile strength, flexural strength, and other desirable properties. However, the choice of composites is affected by operating temperature and fluid resistance requirements, so a good understanding of the expected temperature extremes and environment of the antenna is necessary when designing composite parts.

Figure 3. Modular antenna array, which exhibits wide use of composite materials and conductive coatings in its construction. (Source: TE Connectivity)
Carbon fiber reinforced composites are addressing the need for lightweight, cost-effective, mass-producible electrically conductive parts. Conductive composites typically offer a 30 to 40 percent weight savings over aluminum parts. For antenna applications, use of carbon fiber composites range from ground planes to enclosures.

Glass fiber composites are moldable and offer an economical solution for producing radomes and antenna substrates. Typical radomes are formed using E-glass reinforcement for economical designs or quartz fiber reinforcement when low loss is critically important. Glass fiber composites offer thinner, lighter parts than non-fiber reinforced designs. Glass fibers also increase the dielectric constant of most composites, enabling antenna size reduction when these composites are used as substrate materials. Composite materials can also be engineered to provide “designer” dielectric constants through the addition of various filling materials, such as hollow glass microspheres, conductive particles, or foaming agents.

For both carbon fiber and glass fiber composites, fiber length is an important design parameter. Longer fibers offer more strength but reduced ability to manufacture small features. Moldable long-fiber composites allow significant thickness reductions while maintaining equivalent strength of short fibers. Continuous- fiber reinforcements are attractive for further weight reduction on designs with large, smooth features.

3D Selective Metallization

The typical method of metallizing specific shapes on 3D surfaces is selective plating. This process requires labor-intensive application of physical masks to the surface of the part followed by a multi-step plating process. Because of the high labor content, selectively metallized parts are usually relatively expensive.

Alternative processes include laser direct structuring (LDS) and two-shot molded interconnect devices (MID). Both allow cost-effective 3D metallization, but both are constrained by the range of available substrate materials. In addition, injection molds are required for both these processes, increasing non-recurring expenses and lead times.