Additive Manufacturing for Antenna Applications

*Gregory Mitchell and David Turowski*

### **Abstract**

This chapter describes the results of additive manufacturing (AM) for a multi-band antenna that effectively replaces two with a single footprint. The antenna achieves distinct modes of operation by achieving flexibility between horizontal and vertical polarizations on transmit and receive at both S-band and X-band frequencies. Low dielectric constants of commercial AM materials limit current AM antenna designs. Research into the composition of high-dielectric feedstocks for AM opens the design space for 3D printed hybrid material antennas. We compare the performance of an AM antenna to the same prototype using traditional methods and materials.

**Keywords:** additive manufacturing, dual-band antenna, dual polarization, 3D printing

#### **1. Introduction**

Additive manufacturing (AM), also known as 3D printing, allows engineers to rethink the traditional antenna design space. AM facilitates complex designs that require properties not achievable by current manufacturing methods. The 3D and hybrid-material approaches needed to achieve these designs makes AM critical to the future of radio frequency (RF) systems.

New research is spearheading development of RF AM technology to facilitate development of scalable AM antennas with built-in frequency and polarization agility. AM is a disruptive technology that facilitates complex designs requiring properties not achievable by current manufacturing methods. Strides in AM show robust structural and mechanical parts, but industry has yet to develop and fully characterize a large suite of RF materials compatible with AM methods. Low dielectric constants of commercial feedstocks limit current AM antenna designs. Recent research into the composition of high-dielectric feedstocks and for AM opens the design space for 3D printed hybrid material antennas [1–3]. This research includes loading low-loss polymer matrices such as acrylonitrile butadiene styrene (ABS) with varying volumes of high-dielectric ceramic nanoparticles. However, increasing the volume percentage of high-dielectric ceramics creates brittle filaments, which break when spooled and bind when printing, making dielectric constants greater than 8 unviable for fused deposition modeling (FDM) printers. However, initial research into incorporating the filament extrusion step directly at the print head shows promise by eliminating the need to print from a pre-fabricated spool of filament effectively sidestepping the ceramic volume loading limitation

previously mentioned. This technique could open the doors for even higher dielectric AM filaments because designers will not need to spool or flex the highly loaded polymer in order to print with it.

composites [3–6]. The process loads a low-loss host polymer with a given volume fraction 0f ceramic nanoparticles with high dielectric constants. The host polymer will tend to have a low dielectric constant and the volume fraction of the dispersed high-dielectric ceramic particles will determine the macroscopic dielectric constant of the extruded filament [5, 7]. Since we know the presence of voids during the 3D printing process can cause deviations in the dielectric constant, electromagnetic

AM for hybrid material antennas has additional obstacles other than limitations in dielectric constant. The layered nature of 3D printing causes the potential for inconsistencies in the bonding of interfaces between printed layers. Similarly, 3D printing processes yield anisotropy in the electromagnetic properties of printed layers that can yield RF properties that differ depending on direction within the printed substrate. Porosity, surface roughness, and repetitiveness are also concerns

Beyond dielectric feedstocks for AM, research into increasing the conductivity of printable inks is also of interest. The best conductivity of conductive inks is currently 5–10 times less than that of bulk metals, and even these reduced conductivities require sintering processes in excess of 175°C [12]. Reduced conductivity will cause decreased radiation efficiency in antennas and increased transport inefficiencies in transmission lines. Whereas high sintering temperatures required for 3D printed inks would degrade and melt the thermoplastic-based dielectric compounds discussed previously. There are alternate methods for sintering currently under investigation such as laser sintering and flash annealing, but these methods

characterization of the final substrate becomes very important.

*Additive Manufacturing for Antenna Applications DOI: http://dx.doi.org/10.5772/intechopen.92363*

relating to AM technologies for antennas and RF devices [8–11].

still require further research to demonstrate their viability.

**2.1 High-dielectric filaments compatible with additive manufacturing**

dielectric substrates, and aperture through a fully automated process.

materials are prone to printing defects, such as voids [14].

**191**

Current research investigates methods for extruding high-dielectric AM filaments through a robust and repeatable method that allows for the printing of AM substrates with a given value of dielectric constant. This will give engineers a continuum of achievable dielectric constants for AM substrates they can use in their models when designing RF components. A second challenge is developing a technique for sintering of conductive inks printed on an AM substrate without compromising the integrity of the dielectric substrate. A final hurdle is to produce a fully integrated AM antenna including ground plane, RF connectors, feed, multiple

Typically, composite materials are prepared using mixing techniques such as dissolving pellets of ABS using acetone [12, 13]. Afterward, mixers add plasticizers and surfactants in small concentrations. These additives are necessary, as the plasticizer acts as a lubricant between molecular chains in the polymer, enabling flexibility even with loading of ceramic powders; however, the addition of too much plasticizer negatively affects the composite by rendering it too elastic. Materials use surfactants to prevent aggregation between the ceramic particles [14]. Adding high-dielectric ceramic nanoparticles in in volume fractions between 15 and 30% to the mixtures allows to them to homogenize within the polymer. Once the acetone has fully evaporated, we cut the composite slab into pieces and then ground them into approximately 2-mm pellets. We can then extrude filaments at high temperature, but this process has its limitations. Adding more than 40% by volume of ceramic powder results in a filament too brittle for use, even with the addition of plasticizer. Furthermore, as the loading of ceramic inclusions increases, so too does the viscosity of the material. Designers must exercise care, as viscous

Currently, AM produces robust structural and mechanical parts, but designers have yet to fully develop and characterize electromagnetic properties of AM feedstocks for printing antennas and other RF devices. Recent research into the composition of high-permittivity feedstocks for AM opens the design space for hybrid material antennas, and necessitates an emphasis on the measurement of electromagnetic properties for printed dielectric substrates.

Novel high dielectrics and conductive inks for AM enable complex and integrated antenna designs in all three dimensions. This leads to our integration of our S/X-band antenna into a single aperture allowing for simultaneous multiband capabilities. The 3D and hybrid material approaches needed to achieve this scalable, agile, and multimode antenna demonstrate the necessity of AM for future of RF systems. Additionally, AM enables on demand supply closer to the point of need. This reduces the logistical burden, cost, and upgradeability of RF system maintenance in the field. These benefits result rapid development of new technologies, and increases agility to address new RF needs as they emerge in near real time.

This chapter focuses on the benefits and negatives of AM pertaining to antennas. AM dielectric substrates enable multiband approaches to AM phased arrays. We demonstrate our AM antenna by comparing experimental data to an identical antenna manufactured via legacy materials and techniques.
