In a thesis entitled “Design of Microwave Components using Direct Metal Laser Sintering,” a Waterford Institute of Technology student named Deepak Shamvedi discusses using 3D printing to fabricate several microwave components, including the first-ever 3D printed metal Sierpinski gasket antenna, with multiple resonance characteristics. Shamvedi chose the Sierpinski gasket antenna because of its complexity, aiming to “push the limits of 3D metal printing.”
The antenna was 3D printed using the EOSINT M280 machine and a titanium alloy called Ti-6Al-4V.
“Following the rules of 3D printing, one should acknowledge that even though the Sierpinski fractal design may look simple, but it is complex at the same time,” states Shamvedi. “It consists of an arrangement of stacked pyramids one-upon-another, to form a 3D geometry. A rectangular copper clad PCB ground plane, of 160 mm x 100 mm, with 1 mm thickness, has been used to serve as a finite ground plane to the printed antenna.”
Because the 3D printed version of the antenna could not be realized with infinitely small joints, Shamvedi had to print it in an upside down orientation with a minimum of 1.90 mm base diameter (0.95 mm base radius). This value was chosen to achieve the 3D design without any metal drooping. The base diameter also needed to be big enough to facilitate soldering if needed. The base diameter of the antenna formed a ring-like shape, due to which the effect of the RF performance of the antenna, from increasing or decreasing the width of the ring, has been named the “ring width effect.”
Support structures were required; in order to make them easier to remove, Shamvedi added small holes in the CAD design of the supports. Once the antenna was 3D printed, it underwent a rigorous post-processing routine to remove the supports and reduce the surface roughness of the component. The antenna was then mounted onto feeding circuitry for RF measurements, which were carried out after each stage of post-processing, including wet blasting and polishing, to assess the affect of the surface roughness on the antenna’s performance.
“From the results obtained, increased surface roughness increases the random scattering of electromagnetic waves; therefore, increasing RF resistance, which further reduces the gain of the antenna,” explains Shamvedi. “The antenna RF performance was measured and found to be in good agreement with simulation results, in terms of bandwidth and radiation characteristics.”
Shamvedi also 3D printed a monocone antenna and integrated an N-type feed onto it to create a monolithic structure. 3D printing, he explains, produces fine detail and robust components with low surface roughness. A monolithic structure can also offer better mechanical properties over glue or solder. Despite some challenges, Shamvedi was able to produce a working prototype of a 3D printed antenna, and the measured RF results for the antenna were found to be in good agreement with the CST simulation results.
Shamvedi then compared the performance of three metal 3D printed antennas to that of polymer ones. A metal 3D printed inner lattice antenna possessed higher strength-to-weight ratio than a metal-coated polymer antenna. He also investigated the effects of surface roughness on a 3D printed metal horn antenna, and explored 3D printing as a means to improve the performance of an X-band horn antenna, with the primary goal of side-lobe reduction. Finally, he 3D printed an artificial dielectric lens for applications including 5G.
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