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Cross section view of the corrugated conical horn antenna design

While most 3D printed antennas are made with metal, two researchers from Turkey’s Yasar University recently completed a study about using PLA material to make a 3D printed conical corrugated horn antenna, which is used to feed reflector antennas in direct broadcast satellite (DBS) systems. The paper, titled “The Prototype of a Wideband Ku-Band Conical Corrugated Horn Antenna with 3-D Printing Technology,” discusses the researchers’ design, production, and verification of a prototype antenna fabricated with FDM 3D printing and nickel conductive aerosol painting.

The abstract reads, “The antenna designed with CST Microwave Studio program operates within wideband of 10.5-18.5 GHz at Ku-band. The prototype is realized with new generation 3D printing technology and conductive paint coating method, which makes the antenna lightweight and provides low cost and faster production. According to measurement results, the antenna has return loss almost better than 20 dB, gain value of minimum 14.5 dBi and sidelobe level of -18 dB at most within 1.76:1 frequency bandwidth. Antenna is observed to have a gain loss of at most 1.5-2 dB within the band as compared to the same antenna with high conductivity metal, which needs higher cost and production time for the manufacturing.”

3D printed halves of antenna prototype

Typically, conical corrugated horn antennas are used in dual or circular polarization applications, like satellite communication, and are made up of four main sections: input (feed) waveguide, transition, corrugated profile (mode converter), and the antenna aperture; however, this prototype only has three.

The interior surface slots and teeth in this type of antenna work as a feed for reflectors in remote sensing systems and satellites, due to its “directivity and gain as well as low cross-polarization level, low side and back lobe levels and good return loss value.”

“When there is TE11 mode propagation in the input waveguide section, which is a smooth and flat walled structure, TE11 and TM11 modes propagates in the corrugated surface. The propagation of the both electric and magnetic field components of TE and TM modes are at the same velocity, which results in as a single hybrid (HE11) mode,” the researchers explained. “Therefore, the corrugated surface of the antenna actually behaves like a mode converter. Hybrid mode propagation provides extremely good beam symmetry in radiation patterns with low cross-polarization levels, with high beam efficiency. For these reasons, corrugated horns provide good wide-bandwidth performance.”

Assembled antenna structure

Because they are made up of complex geometric shapes, you need a highly precise manufacturing process to make these. CNC and CCM machines are used most often, but they’re expensive and take a long time, which is why some people choose to use FDM 3D printing.

This antenna was specifically designed to operate within wideband between 10.5 and 18.5 GHz, so it can cover both the general RX band (10.5-12.75 GHz) and TX band (17.3-18.4 GHz) in DBS communications and the TX/RX bands of 10.7-12.75 GHz and 13.75-14.5 GHz in telecommand and telemetry satellite applications. Simulations within CST Microwave Studio 2017 were used to optimize these dimensions, first using Perfect Electric Conductor (PEC) material to make the process faster, and then with dielectric PLA and the nickel conductive aerosol paint coating.

“Besides, the results with PEC material are used as reference results for comparison such that they can be approximately taken as the results when the antenna is manufactured with CNC machine and high conductivity material such as aluminum,” the researchers explained.

“From the simulation results given for the coated antenna, it can be concluded that PLA/nickel materials have quite slight effect on the return loss performance of the antenna where the return loss values are almost above 20 dB for 10-19 GHz. The values slightly drop below 20 dB for the frequencies around 10 GHz. This is due to the reason that the coating thickness on PLA decreases the inner dimensions of the antenna including the feed rectangular waveguide. Therefore, the cutoff frequency of the waveguide (and the antenna) becomes closer to 10 GHz, at which the return loss of the antenna is deteriorated.”

Return loss measurement setup

An Ultimaker 2+ was used to manufacture the antenna prototype out of PLA, which is easier, cheaper, and more environmentally friendly to print than ABS. A 0.4 mm nozzle was used to apply 0.2 mm layers, with 50% infill, at 50 mm/second, which took about 23 hours.

Measuring directivity and radiation patterns

“After printing, the identical parts are coated by using three coats of Super Shield-841 nickel conductive aerosol paint spray to give the coating thickness of approximately 0.1 mm. Finally, the fabricated half-pieces are assembled by combining them with a special adjustable clamp system,” the researchers noted. “After the manufacturing steps are completed, the total weight of the prototype antenna is measured as about 230 gr, which is sufficiently lightweight.”

The performances – directivity, radiation patterns, realized gain, and return loss – of the antenna were measured. Additionally, the researchers compared the cost, production cost, and weight of the antenna when made with 3D printed PLA and nickel, and one made out of aluminum with CNC-based milling.

Not surprisingly, the research shows that the 3D printed prototype takes less time and money to make, and is also more lightweight.

“Although a conductive material (nickel) with moderate conductivity is used for spray coating with a thickness of about 0.1 mm, it is found from the measurements that the antenna gives not more than 2 dB gain loss as compared to same antenna manufactured with high conductivity material and CNC-based manufacturing. The proposed antenna structure manufactured with proposed technique still has highly satisfactory performances such that it provides more than 17 dB return loss, 14.5 dBi gain and peak sidelobe level of -18 dB in E-plane and H-plane at the given frequency band (1.76:1 bandwidth),” the researchers concluded. “The proposed fabrication technique has the advantages of low weight, low cost and low production time as compared to CNC-based production in spite of slight loss in the gain. As a conclusion, 3-D printing and coating method is very useful especially for research and prototype verification in antenna and microwave systems.”

Co-authors of the paper are M. E. Carkaci & M. Secmen.
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