3D printer

Ultralight Wide-band Double Ridged Horn Antenna Using Additive Technologies

3 September 2021by alexandre.manchec
antenne cornet double ridge ultra légère

Introduction

Lightweight devices and fast prototyping are two burning issues in the radiofrequencies (RF) field. Yet, the always increasing complexity of RF structures and the development of the new shapes inherently lead to longer development time and heavier devices, and thus, higher cost. To overcome some of these challenges, namely cost and manufacturing time, it was recently proposed to use the emergent 3D printing technologies [1]. These new techniques, so-called Additive Manufacturing (AM), are becoming widely accessible and offer an interesting alternative to conventional manufacturing techniques. Evaluation of the efficiency of the 3D printing technology can be found in the literature [2]. However, most authors are considering only simple horn antennas using conventional coaxial to waveguide feeds, only a few papers describe more complex structures [3]. Nevertheless, the technique described in [4], hardly applicable to conventional manufacturing, allow to significantly reduce the weight of a 3D printed structure without decreasing its radiofrequency performances by perforating the structure with multiple electrically small holes.
In this paper the authors proposed a 3D printed double ridged horn antenna operating in the 2 GHz to 18 GHz frequency bandbased on a commercially available antenna. This latest antenna realized using conventional machining manufacturing presents a weight of 380 g. The same ridged horn was realized by the authors using AM technologies with a weight of 180 g, keeping the same form factor as the original antenna,and was then lighten to 76 g, i.e. 80 % weight reduction, with similar RF performances. However, one of the main concern regarding plastic impressions is the power handling of the final device. In order to test the antenna power capabilities it was submitted to a thermal test. Indeed, a third antenna was manufactured with a specific resin having good thermal properties. The results show a good behavior of the antenna reflection coefficients over a temperature of 150 °C

Antenna design and manufacturing

The antenna was printed using stereolithography (SLA) 3D printing technique, namely the Formlabs Form 2 printer, and a White v4 resin. The resolution of the printer with this specific resin is 140 µm in the xy axis (laser point diameter) and 50 µm in the z axis (layers thickness). The dimensions measurements of the printed antenna show a good correlation with the announced accuracy value with variations inferior to 100 µm. The antenna was then metallized using a conventional plating  metallization process: (i) surface roughness enhancement by dry sandblasting, (ii) palladium catalysis, (iii) 3-µm chemical copper deposition, (iv) 10-µm electrolytic copper deposition and (v) 10-µm electrolytic tin deposition.

The  antenna was design for ultralight (UL) purposes. Indeed, the new method proposed by Huang in [4] allows to drastically decrease the total weight of an RF device without impacting its performances. This method consists in the perforation of all the walls with multiple periodic holes which have subwavelength dimensions. These holes are 3 mm squares which corresponds to a physical length of 0.18 λ at the maximum operating frequency (18 GHz). The holes unit cell, of periodicity 4.6 mm or 0.276 λ, is depicted in the Fig. 2. It has to be noted that the thickness of all walls has also been redu

The antenna was printed using stereolithography (SLA) 3D printing technique, namely the Formlabs Form 2 printer, and a White v4 resin. The resolution of the printer with this specific resin is 140 µm in the xy axis (laser point diameter) and 50 µm in the z axis (layers thickness). The dimensions measurements of the printed antenna show a good correlation with the announced accuracy value with variations inferior to 100 µm. The antenna was then metallized using a conventional plating  metallization process: (i) surface roughness enhancement by dry sandblasting, (ii) palladium catalysis, (iii) 3-µm chemical copper deposition, (iv) 10-µm electrolytic copper deposition and (v) 10-µm electrolytic tin deposition.

The  antenna was design for ultralight (UL) purposes. Indeed, the new method proposed by Huang in [4] allows to drastically decrease the total weight of an RF device without impacting its performances. This method consists in the perforation of all the walls with multiple periodic holes which have subwavelength dimensions. These holes are 3 mm squares which corresponds to a physical length of 0.18 λ at the maximum operating frequency (18 GHz). The holes unit cell, of periodicity 4.6 mm or 0.276 λ, is depicted in the Fig. 2. It has to be noted that the thickness of all walls has also been reduced from 3 mm to 2 mm and the back mounted plate has been optimized as its minimum size. The UL antenna design and a photograph of the manufactured body following the same printing and metallization process as the first antenna are shown in Fig. 3.

ced from 3 mm to 2 mm and the back mounted plate has been optimized as its minimum size. The UL antenna design and a photograph of the manufactured body following the same printing and metallization process as the first antenna are shown in Fig. 3.

https://www.elliptika.com/wp-content/uploads/2021/08/antenne-allege.png

Figure n°1 View of the simulated UL antenna

antenne cornet double ridge ultra légère

Figure n°2 photograph of the manufactured UL antenna

https://www.elliptika.com/wp-content/uploads/2021/08/antenne-allege-1.png

Figure n°3 : Perforation unit cell (dimensions given in mm)

https://www.elliptika.com/wp-content/uploads/2021/08/mesure_UL_antenna.png

Figure n°4. (a) Simulated and measured S11 of the conventional double ridged antenna compared to the ultralight version; (b) Simulated radiation patterns of the conventional double ridged antenna compared to the ultralight version.

Simulation and measurement

The plastic printing allow to reduce the total weight by 56 % due to the relative density reduction of the material from 2.7 g/cm3 for aluminum to 1.17 g/cm3 for the resin. Then the reduction of the all walls thickness from 3 mm to 2 mm reduces the antenna weight of an additional 30 %. Finally, the perforation of the antenna reduces the weight by 39 %. The total weight reduction of the printed ultra-lightweight antenna compared to the machined one is 80 %.

The measured S11 of the manufactured antennas are compared to the simulations in the Fig. 4(a).The radiation patterns of the antennas have not been measured in an anechoic chamber yet, however, the simulated radiation patterns of both conventional and UL antennas are compared in the Fig. 4(b). The perforations on the UL antenna do not affect the electrical performances and thus, presents the same results as the initial antenna, both in matching and in radiation. However, a lower maximum gain can be expected in measurement due to a higher surface roughness in the case of a printed antenna. The roughness of the printed antenna was measured at 12.5 µm

Conclusion

In this work, a method to reduce the weight of RF structures by perforating walls is applied to a double ridged horn antenna operating in the frequency band from 2 GHz to 18 GHz. The antenna is manufactured using a stereolithography 3D printing method followed by a wet metallization process. The results show a reduction of the weight by 80 % from 380 g for the machined antenna, to 76 g for the printed ultralight version. The measured performance of this latest antenna are measured similar to the conventional one. Finally, a thermal test was performed in order to predict the behaviour of such a 3D plastic printed antenna at high power levels. Using an high temperature properties materials, the UL antenna kept good performances up to a temperature of 150°C.

REFERENCES
[1] I. Gibson, et al., “Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing”, Springer-Verlag, 2010
[2] H. Yao, et al., “Ka band 3D printed horn antennas”, WMCS 2017, Waco
[3] B. Zhang, et al., “Metallic, 3D-Printed, K-Band-Stepped, Double-Ridged Square Horn Antennas”, Appl. Sci. 2018, 8(1), 33
[4] G. Huang, et al., “Lightweight Perforated Waveguide Structure Realized by 3-D Printing for RF Applications”, IEEE Trans. Antennas Propag., vol. 65, no 8, p. 3897-3904, 2017.

Authors : J. Haumant1,2, G. Cochet1, D. Diedhiou1, A. Manchec1, R. Allanic2, C. Quendo2, C. Person3, R.-M. Sauvage4

1Elliptika, 2 rue Charles Jourde, 29200 Brest, France

2Univ. Bretagne Occidentale, UMR6285, Lab-STICC, 29200 Brest, France

3IMT-Atlantique, UMR6285, Lab-STICC, 29200 Brest, France

4DGA, 60 Bd Général Martial Valin, 75000 Paris, France