Manufacturing Considerations in the 3-D Printing of Fractal Antennas

Abstract

The use of additive manufacturing (AM) techniques for the fabrication of 3-D fractal monopole antennas is presented. The 3-D printing (3-D P) of 3-D designs based on the Sierpinski fractal concept is studied, and the performance discussed. The AM allows the fabrication of the complex features of these antennas. The specific structures, on the other hand, provide a reduction of the material used in AM compared with the equivalent nonfractal designs, in which two cases can be described by over 75%. This is the first time that 3-D fractals have been studied in terms of volume reduction and their potential benefits to AM of antennas. The first investigated antenna derives from the Sierspinki tetrahedron fractal shape. From this initial design, two new structures have been developed: the dual Sierpinksi fractal and the dual inverse Sierpinski fractal. The new designs offer improved matching and radiation pattern. All the antennas operate at 2.4 GHz used in Bluetooth and wireless LAN band. Furthermore, the final inverse fractal shape is able to cover both the 2.4- and 5.5-GHz WLAN frequencies with a reflection coefficient ( $S_{11}$ ) better than −10 dB, together with coverage at bands around 8 GHz. This ratio of resonant frequencies is achieved after a series of described design stages. The radiation patterns of the antennas are monopole-like at both bands. The AM technique employed is metal powder embinder printing where a binding material is jetted on a powder bed containing metal particles. Metal 3-D P is ideal for maintaining the mechanical strength of the structures. The envisaged applications are in the defense and aerospace sectors where high-value, lightweight, and mechanically robust antennas can be integrated with other 3-D printed parts. Transient simulations based on the finite integration technique compare well with measurements.