1 Introduction
In this study, the Design Thinking (DT) method is used to develop a 3D printed radio frequency antenna, which is an important part of a comprehensive industrial digital system. It utilizes the established human-centered DT methodology [1, 2], which is typically divided into five phases: empathize, define, ideate, prototype, and test. Since it is impractical to test the entire system with a 3D-printed component in this study, we examine the system from the perspective of a manufactured component. DT tools provide a lens for visualizing new perspectives and understanding system complexity. Previous studies have shown their usefulness in 3D printing as a teaching aid [3]. This study investigates their use in industrial applications. The following previously validated DT methods were used:
Empathy: This step defines the background of the context and the users of the device, exploring their behavior through open-ended questions. The goal is to understand the users’ needs by putting yourself in the user’s position.
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Define: Based on the collected data, a summary of the problem to be solved is made. An action-oriented approach is used to effectively express the demands of stakeholders.
Ideate: This stage is dedicated to generating ideas to solve the problem. Ideas are shared and discussed openly. This phase includes benchmarking, analysis of current solutions, functional decomposition and Design for Manufacture and Assembly (DfMA) methodology.
Prototype: The phase involves refining the idea and alternative solutions through concept description, in which all team members participate. It also includes creating CAD concepts to convert ideas into visual design.
Test: This step involves evaluating the concept and gathering feedback.
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In the DT method, the assigned antenna can then return to an earlier step, such as ‘Define’ or ‘Ideate’, based on the findings of those steps.
Empathy: Three-dimensional (3D) printing of antennas and microwave components has received considerable attention in academia, leading to the development of innovative printing techniques covering a variety of materials, including dielectric, magnetic, conductive, and even self-healing materials [4‐9]. Although multi-material 3D printing opens up new opportunities in device design by overcoming the limitations of stacking “2D” layers [8], [10‐16], it has yet to be considered for mass production in industrial applications. It is typically compared to traditional manufacturing processes such as machining and injection molding and is often considered to be limited to prototyping due to its relative slowness. However, 3D printing enables the creation of more complex structures that cannot otherwise be achieved with traditional methods [17‐21]. The scalability of 3D printing, proven in eyewear production, is also often overlooked when it comes to manufacturing speed. Modular manufacturing, a design approach that covers multiple technical functions, is an integral part of this technology [22‐25].
We studied the technology of the European Regional Development Fund ERDF, the Council of Oulu region, the University of Oulu and the companies Nokia Oyj, UPM-Kymmene Oyj, Carbodeon Ltd Oy, 3DTech Oy and collected their views on the development of technology. There were different groups such as researchers, professors, production technology designers, production technology users, companies’ R&D Managers and representatives of research funders. In the study, their ideas were collected and the initiatives to manufacture the components were discussed in joint idea meetings. In addition, the general background information from the sector, from component requirements to industrial needs, and current research information were available. At first, company representatives wanted to try the technology in the manufacture of simple structures, such as transmission lines operating at radio frequency, taking into account the special tools enabled by the device as well as the measurement of material properties and other quality indicators related to manufacturing, e.g. surface roughness. From these initial studies, which are not discussed in this article, it was started to carry out the 3D printing research of the antenna. From the point of view of company representatives, the focus was on prototype manufacturing and the possibilities of mass production were seen as limited. The problems in the field are antennas made of several parts, which causes costs for manufacturing and assembly. In addition, the complexity of multi-layer structures and antenna feed network worries the engineers responsible for manufacturing. The antenna should be simple and should support the affordable mass production of the rest of the product structure.
Define; Two specific research questions related to industrial product structure are related to the design and manufacture of a 3D printed microwave module antenna. The use of modular product design enables cost optimization in manufacturing and maintenance, because individual parts can be manufactured, replaced and tested without having to replace other components related to the product structure in the event of a possible failure. On the other hand, in connection with antenna modules, one critical and challenging aspect is the design and manufacture of the antenna feed structure or network, for which alternative ways have been sought for several years.
Ideate; Therefore, the first research question aims to find out how 3D manufacturing using both insulating polymers and conductive composites can be used to realize a modular layered structure for a parasitic patch antenna in a single manufacturing process without intervention or post-processing. The term “layered structure” refers to a structure that contains internal air-filled cavities, while “module” refers to interchangeable parts as well as combining multiple functions into a single structure. Another special issue in antenna technology concerns the effect of the 45-degree angle feed arrangement on patch antenna performance. Such structures have been discussed previously in the articles mentioned above. By moving the patch antenna further from the reflector, the radiation properties can be improved, in which case the antenna feed line must be raised in the raised patch area when sending signals from the same level as the antenna reflector. This placement allows the reflector to act as a grounding conductor. The input structure also considers the impedance distribution and strives to achieve the widest possible bandwidth in the frequency plane. A multi-antenna design with a complex feed distribution network that should still be broadband and low loss is a list of requirements that lead to conflicting results and expensive manufacturing implementations. In this paper, we present a fully printed modular parasitic patch antenna operating at 8.5 GHz (higher band beyond 5G telecommunications) with two identical polarization feeds at 45 degrees. The antenna was made using a multi-material 3D printer that can automatically switch between insulating and conducting material. Our contribution is to present the buried air cavity and antenna feed structure created by printing technique, which are important new structures in this application area. In addition, the manufacturing technology introduces the use of printing for both conductive and insulating materials, which represents a new area of application. The measured electrical results of the structure correspond well to the simulated results, which supports the motivation for further technological developments.
The study is partly highlighted by a Set Based Concurrent Engineering (SBCE) that represents Toyota’s innovative approach to product development, which aims to identify and evaluate a wide range of solutions for each product subsystem. This method involves a step-by-step search and refinement process that ultimately leads to the selection of an optimal solution [26]. In this study, however, we adopt the DfMA methodology, which emphasizes improving manufacturing and assembly efficiency in the product design phase [27]. DfMA combines two key methods, namely Design for Manufacture (DFM) and Design for Assembly (DFA).
DFM focuses primarily on achieving cost-effective production by carefully selecting materials and manufacturing processes that minimize costs and maintain product quality. It considers factors such as material costs, production efficiency and tooling requirements to ensure economical manufacturing. In this study, the DFM is applied to the use of additive manufacturing in the printing of both insulation and conductor material. In addition, DFM aims to simplify manufacturing operations by designing parts that can be easily manufactured using selected manufacturing processes, minimizing the need for specialized equipment or complex techniques. We apply the design and structural manufacturing perspective of 3D printing, which is introduced at the beginning of the next paragraph. In addition, DFM aims to reduce material waste and promote sustainable development by promoting the efficient utilization of materials and taking recyclability aspects into account. Furthermore, DFM takes into account the limitations and characteristics of the chosen production methods, ensuring that production meets quality standards. The performance of the antenna product was evaluated especially with electronic measurements that refer to the product’s customer requirements.
On the other hand, DFA focuses on streamlining the assembly process. It achieves this by designing parts that align, connect and assemble smoothly, reducing the number of assembly steps and the time and effort required for assembly. In this study, the DFA perspective is considered within the scope of possibilities, but it cannot be definitively verified in the products in question, for example mobile phone base stations. In addition, DFA aims to minimize assembly costs by designing parts that are easy to handle, place and assemble, reducing labor and equipment requirements and resulting in cost savings. DFA considers the ease of product maintenance and serviceability by designing parts that are easily accessible, replaceable or repairable, effectively reducing cellular network downtime and improving the overall product life cycle. In addition, DFA improves product quality through careful assembly design, ensuring accurate and safe assembly of parts, thereby minimizing risks associated with misassembly, misalignment or component damage, improving product performance and reliability. The above-mentioned DFA goals cannot be verified in this study, but the aim is to improve their conditions as much as possible.
2 Materials and methods
Prototype; The proposed antenna design integrates the principles of DfMA to enhance manufacturing efficiency and assembly effectiveness. The modularity of the antenna is achieved using replaceable main and parasitic radiators, enabling easier installation and potential customization. Figure 1 showcases a 3D model of the antenna structure, demonstrating the application of DfMA perspectives. 3D printed snap-in mechanism edges are incorporated to facilitate assembly and positioning. The antenna structure comprises a reflector measuring 39 × 39 mm², featuring two staggered support structures in the middle that elevate the main antenna (13 × 13 mm²) by a distance of 2.5 mm from the reflector. Additionally, another slightly larger structure raises the parasitic patch (11 × 11 mm² conductive surface) by 1.7 mm from the main antenna. This simple and symmetrical design allows for the implementation of two identical 50-ohm feed lines positioned at a 90-degree angle to each other. These feed lines are connected to the raised main radiating patch using 45-degree slopes. This configuration facilitates investigation of the manufacturing accuracy of the printed feed lines without necessitating a second identical antenna.
In terms of materials, the antenna design employs two different printable materials: insulating polycarbonate and conductive silver lines. The dielectric constant (εr) and loss tangent (tanδ) of the black polycarbonate were determined to be 2.71 and 0.00918, respectively, using the Split Post Dielectric Resonator (SPDR) method at 5.18 GHz. The conductivity of the printed silver paste is 3.14 × 10^6 S/m, which corresponds to approximately 5% of the conductivity of bulk silver measured at direct current (DC).
For the antenna simulation, CST Studio Suite software was utilized. The optimization process involved adjusting the widths of the feed lines, particularly the 45-degree line, as well as modifying the sizes and distances of the main and parasitic antennas. These optimizations were implemented to enhance the performance and efficiency of the antenna design, taking into account the manufacturing and assembly aspects influenced by the DFMA approach. The simulation model was developed with a focus on the 3D printing model rather than the reverse.
While the antenna structure lacks a resolved connection for bringing the signal to the developed antenna, SMA connectors are currently utilized for measurement facilitation. In the future, these connectors could be reinforced, for example, with printable conductive glue. The printed structure allows for further development or alternative construction methods from the perspective of the SBCE method. For instance, the antenna radiators could be printed as a single piece, offering an alternative to the chosen structure. It’s important to note that the current structure necessitates manual labor to assemble the parts together.
Fig. 1
A 3D printable model of the proposed modular parasitic patch antenna (units are in mm)
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3 Results and discussion
The antenna was fabricated at the University of XX using Neotech AMT’s modular additive manufacturing system, specifically the model 15X G4 (Fig. 2). This platform, equipped with a 5-axis motion module (comprising three linear and two rotary axes), allows for the printing of complex 3D electronic circuits without the need for support structures. The system demonstrates exceptional accuracy and repeatability in the movement of the linear axes (X, Y, Z), with ± 5 μm and ± 1.5 μm tolerances, respectively. The rotary axes (A, B) exhibit movement accuracies of 1.5 arc minutes and < 6 arc seconds.
The system encompasses various pre- and post-processing tools that can be classified into three groups based on their purpose: (1) addition tools, (2) subtraction tools, and (3) calibration/measurement tools. For the fabrication of a double polarized patch antenna, which adheres to the DFM principle of ease of design to manufacture, tools from each group were employed. To print thermoplastics and silver ink, a fused filament fabrication (FFF) module was used, featuring an E3D (V6 hot end Titan extruder) and a Nordson PICO Pulse piezo jet (PJ). Excess material was removed and the substrate was polished under the areas where the silver ink was deposited using Imes-icore GmbH high-frequency CNC milling. Additionally, the system incorporates cameras for tool calibration and part alignment during the manufacturing process, ensuring DfMA compliance for product tolerance management. Surface roughness analysis of CNC-machined and 3D-printed surfaces was performed using Bruker’s Contour GT-K0 optical surface profilometer, revealing Ra values of approximately 625 nm and 11.0 μm, respectively. Although not mandatory, polishing the FFF-printed surface prior to silver ink spraying enhances the quality of the printed silver patterns, such as the parasitic emitter and patch. This outcome represents a significant advancement in the development of 3D printing technology for microwave applications.
The antenna manufacturing workflow was divided into several sub-phases. It commenced with the production of the antenna base or reflector body using the FFF and CNC modules. The reflector body, fabricated with Polymaker’s Polymax polycarbonate (PC) filament, was 3D-printed through FFF. The nozzle and platen temperatures were set at 260 °C and 100 °C, respectively, following the manufacturer’s recommendations. To achieve a robust structure, the toolpath of the FFF printer was designed with an approximate 2.5% overlap, ensuring 100% infill. The thickness of the reflector body around the connectors was CNC machined to 0.5 mm, while the remaining areas were maintained thicker for improved durability. CNC was also employed to create pockets in the reflector body, facilitating the embedding of the main antenna and parasitic radiation. The patch antenna and parasitic radiator were fabricated as 0.5 mm thick square plates using the same methodology (refer to Fig. 1 for dimensions). Prior to printing the conductive films, the reflector body and patch antenna were assembled. All conductive elements were printed on the PJ module using Henkel’s ECI10111 silver ink. The expected line width tolerance on a surface polished with a 50 μm nozzle was ± 0.1 mm. To ensure a continuous pattern, the tool path density for filling was set at 0.4 mm, and the feed speed was maintained at 900 mm/min. The print parameters for the drive electronics were set according to the supplier’s recommendations. Adhering to these measures and continuously improving upon the DFM principles maximizes compliance and minimizes handling issues in 3D printing for similar products.
After printing, the semi-assembled antenna and parasitic radiation were cured in an oven at approximately 100 °C for approximately 30 min, allowing the ink to solidify. The SMA connectors were affixed to the supply lines using conductive silver glue (Silver Conductive Paint, SCP, Electrolube), with the connection further reinforced using a two-component epoxy. An electrically conductive copper strip was attached to the back of the antenna, serving as a reflector/ground plane. Finally, the parasitic transmitter was affixed to the antenna base, thereby completing the structure before antenna performance measurements. Empirical evidence indicated that achieving robustness in the antenna’s mechanism, particularly through gluing connectors, is a crucial step to ensure sufficient mechanical strength. This aspect can be monitored by measuring the impedance matching of the antenna. Attention should be paid to achieving tolerances in line with the DfMA principle and ensuring simple assembly, as any delamination from the conductor-insulator interfaces would be detrimental. Figure 3 presents an image of the finished antenna, where the insulating material PC is depicted in black and the conductive silver in gray.
Fig. 2
Neotech 15X G4 modular additive manufacturing system
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Fig. 3
Photos of assembled and measurement-ready antenna, a) from top picture, b) perspective picture, c) side view, air cavity picture
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4 Antenna measurements and simulations results
Testing; The success of the antenna manufacturing process was evaluated by comparing the characteristics of the fabricated antenna to the simulated results. The reflection coefficient (S11) of the antenna was measured between 6 and 11 GHz from both ports, and the results are presented in Fig. 4. The simulated results for both ports were identical, while the measured reflection coefficients between the ports showed slight differences (with a standard deviation of 0.3 GHz compared to the simulated value). Port 1 exhibited a minimum reflection coefficient at approximately 8.1 GHz, whereas Port 2 had a minimum at around 8.7 GHz. The measured minimum levels of the reflection coefficient were approximately − 15 dB, with a bandwidth of approximately 500 MHz at -10 dB for both ports.
Although the antenna was not optimized or tuned after manufacturing, the results were satisfactory. By iterating the design and manufacturing cycle, it would be possible to bring the reflection coefficient from both ports even closer to each other and closer to the simulated value. From a DfMA perspective, a statistical approach to manufacturing multiple products with incremental improvements to the 3D printing process would be an interesting research topic. The efficiency of the antenna was measured using Satimo Starlab 8–10 GHz, and the measurement results are shown in Fig. 5. When Port 1 was used, the antenna’s efficiency reached a maximum of approximately 75%, while for Port 2, it was around 70%. The frequencies corresponding to the maximum efficiency values were similar to the best values of the reflection coefficient. Within the 500 MHz bandwidth range, the efficiency values remained stable. Furthermore, the manufactured structure demonstrated mechanical stability, and the reflection coefficient did not change when the antenna was handled.
Figure 6 presents the measured and simulated radiation patterns of the antenna when fed from Port 1 at phi0, phi90, and theta90 levels. The measured patterns at phi0 closely resembled the simulated results, with a gain of approximately 7.5 dB and a main beam angle of 60 degrees in the drilling direction. The measured patterns at phi0 and phi90 exhibited symmetry, while in the theta90 plane, the positions of the antenna connectors were expected to be visible. Figure 7 illustrates the radiation patterns of the antenna when fed from Port 2. The simulated and measured phi0 patterns were similar to those measured from Port 1, although the gain was slightly lower at approximately 7.2 dB. The measured phi0 and phi90 patterns also displayed symmetry, and the positions of the connectors were likely visible in the theta90 plane, albeit in different directions compared to Port 1.
In comparison to suspended antennas fabricated through photolithography processes or hand-assembled from printed circuit boards (PCBs), the antenna in this study was entirely manufactured using a 3D printer and assembled by hand due to its modular design and the absence of a 3D printer pick-up tool. It was observed that the conductivity of the printed silver was significantly lower than that of bulk copper. However, the measured total efficiency of the presented antenna reached 75%, and its gain fell within the same range (~ 7.5-9 dBi) as that of conventional antennas fabricated using alternative methods. Further optimization of the manufacturing parameters could improve the efficiency ratio using the same materials so that the goal of more than 90% could be achieved.
Overall, the DFM principles fit very well together with the research of the DT method and 3D printing to enhance the manufacturing of microwave products. This method enables a reduction in the number of parts required for production, simplifies assembly by eliminating additional connecting parts, and ensures compliance with technical requirements. The manufacturing process offers advantages such as material efficiency, shorter processing and product development times, and the ability to produce technically complex structures with ease. Although the antenna structure investigated in this study is just one component of a larger base station antenna, the modular manufacturing method employed facilitates testing, assembly, redesign processes, and cost-effective product maintenance for the entire base station. The 3D printer used in this study supports different manufacturing heads for various steps in the printing process, and it includes tools for controlling product tolerances, facilitating DFA planning. However, these aspects were only partially examined in this study. While the overall manufacturing of the microwave component was successful, there are still several areas for further development in 3D printing. One potential view is to employ a statistical approach by manufacturing multiple similar pieces of antennas. Additionally, key design factors such as line impedances, feed impedances, antenna gain, and efficiency could be further investigated to reduce the limitations of the currently used insulation materials. Furthermore, attaching the antenna to a separate support structure that models the base station motherboard would enable the examination of the connection surface between the antenna and the motherboard, thereby studying its impact on product usability and further integrating DfMA principles into future product development and research. The general structure of the 3D printed product pleased the research group, especially because the electrical performance was quite insensitive to the mechanical handling of the antenna. The design of the 3D printed antenna turned out to be slightly different from previously used antenna design techniques, which somewhat surprised the researchers. However, it was easy to adapt to the change of perspective, and it did not significantly hinder the technical implementations. The final result positively surprised the evaluators and changed the perspective from prototype production to the possibilities of wider mass production, as long as a few technical requirements could still be met.
Numerous studies, as summarized in Table 1, have explored the printing of either insulator or conductor materials in microwave components [28‐31]. However, to align with the goals of the DfMA principle, it is crucial to utilize both types of materials simultaneously. The 3D printer used in this study proved to be excellent in achieving this objective. It offers the potential to simplify the production of products even more compared to the hybrid manufacturing, where a combination of 3D printing and traditional manufacturing methods is employed. In the present study, the aim was to come as close as possible to the ideal implementation of the antenna manufacturing process and to investigate its limitations and directions for improvement. Considering all aspects of DfMA, including product maintenance, a fully 3D printed antenna could be manufactured near the maintenance site. Similarly, the product’s lifecycle and the recycling of materials can be better managed by taking advantage of 3D printing technology.
In summary, by integrating both insulator and conductor materials in the 3D printing process, the study aligns with the objectives of the DfMA principles. The 3D printer used offers promising possibilities for simplifying production processes, optimizing manufacturing from the initial stages, and addressing aspects such as product maintenance and material recycling.
Fig. 4
Measured and simulated reflection coefficient of the antenna. Simulated port 1 and 2 were identical, measured values do differ due the fabrication
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Table 1
suspended antennas have been fabricated in several different ways
Multimaterial 3D printed structures | Gain dBi | Frequency GHz | Substrate material | εr and loss tanδ of the substrate | Fabrication of conductive lines | Conductivity* S/m | Antenna type | Ref |
|---|---|---|---|---|---|---|---|---|
no | 9 | 77 | Corning Pyrex 7740 (Glass substrate) | 4.4, loss not reported | photolithography + Electroplated Copper | 5.86 × 107 | Suspended patch antenna | [28] |
no | 8.95 | 3.3 | FR4 (Glass-reinforced epoxy laminate) | 4.4, 0.02 | Etching the copper layer and soldering of metal walls to the lifted patch | 5.86 × 107 | Suspended patch antenna | [29] |
no | 8.15 | 5.2 | F4BME220 (Teflon based laminate) | 2.2, 0.001 | Etching the copper layer and using screws to lift the patch plane | 5.86 × 107 | Slot fed parasitic patch antenna loaded with suspended rods | [30] |
yes | 2.34 | 6,5 | Ag2MoO4 (ceramic) | 10.99, 0.005 | Printed silver powder and microwave sintering | - | monopole antenna with artificial magnetic conductor | [31] |
yes | 7.5 | 8.5 | Fused filament fabrication of polycarbonate | 2.71, 0.009 | Piezo jetting ECI 10,111 silver ink on 45-degree slopes | 3.14 × 106 | Suspended modular parasitic patch antenna | This work |
Fig. 5
Measured total efficiency of the antenna
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Fig. 6
Measured and simulated gain radiation patterns of the antenna when port 1 was fed (scale is in dBi)
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Fig. 7
Measured and simulated gain radiation patterns of the antenna when port 2 was fed (scale is in dBi)
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5 Conclusions
Based on the DT design method, especially with DfMA method, manufacturing and measurement results presented in this study, the manufacturing of a suspended modular parasitic patch antenna with air cavities using 3D printing technology has been successfully demonstrated. The antenna structure was created using both insulating and conductive materials, using as little manual assembly as possible. The measurement results match the expected values, which confirms the antenna’s performance.
The efficiency of the fabricated antenna was high, reaching about 75%, and the gain was about 7.5 dBi. The reflection coefficient was measured to be about − 15 dB and the beam angle of the main beam of the radiation pattern was 60 degrees. The measured radiation patterns and port impedance matched the simulated values. The implementation of a two-level feed arrangement with diagonally printed substrates allowed the feed lines to be successfully connected to the fabricated conductor lines at an angle of approximately 45 degrees. The manufacture and assembly of the antenna was simple and efficient.
In addition, the mechanical and electrical stability of the antenna structure was observed, as the reflection coefficient remained the same even when handling the antenna. The lower conductivity of the conductive lines did not negatively affect the efficiency or gain of the antenna, suggesting that this feature can be exploited in the development of unique and exclusively 3D-printable antennas in the future. The presented antenna model has possibilities for assembly using a printer, and only a pick-and-place tool is required. The study demonstrates the successful fabrication and performance of a suspended modular parasitic patch antenna using 3D printing. The achieved results emphasize the possibility of utilizing both insulating and electrically conductive materials in the manufacturing process, and the antenna design demonstrates the ease of manufacturing and assembly. The stability of the structure and the low effect of lower conductivity open up possibilities for future development in 3D-printable antennas. The findings of this study contribute to the growing body of knowledge in the field of 3D printed microwave components and inspire further research in the design and fabrication of antennas using additive manufacturing techniques. The DT design method is usable and useful in the manufacture of microwave components when you want to use new manufacturing techniques previously unknown in such applications.
Acknowledgements
This work was supported partly by Academy of Finland 6G Flagship under Grant 346208 and partly by European Regional Development Fund Novel Digitally Fabricated Materials for Electronics, Optics and Medical Applications under Grant A74080.
Declarations
Competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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