# Additive Manufacturing of Variable Density Lenses for Radio Frequency Communications in X-Band
## 6 Conclusions  
In this work, we have designed, fabricated, and experimentally validated three GRIN-lens realizations for a compact X-band horn-lens assembly. Experimental measurements showed that lens B achieved the highest performance--measured directivity of 22.1 dBi and aperture efficiency of 55.8%--with a total lens weight of 207 g, see Table 5. Consequently, lens B is identified as the optimal solution for the envisaged compact X-band satellite-communication application. This result demonstrates the effectiveness of full-wave adjoint optimization, coupled with additive manufacturing, in producing application-specific high-performance RF components.  
Furthermore, the GRIN-lens antenna presented in this work was designed for terrestrial satellite-ground communications, where environmental conditions (temperature, humidity, and mechanical loads) remained within the operational limits of polymer-based 3D-printed dielectrics. Nevertheless, the study of 3D-printed materials for RF Applications in space flights is a current trend [43]. It was demonstrated that the metallized polymeric materials (Rigid 10K and Composite-X), as used here, can be space-qualified [44]. As for other polymers used in this work, they may exhibit significant outgassing in vacuum and cannot withstand the extreme thermal cycling encountered in space, so further research is required. Consequently, the GRIN-lens antenna design proposed in this work may be suitable for deployment on the payload of a satellite, with substantial modifications. Future adaptation for spaceflight would require substituting the polymer GRIN lens with space-rated dielectrics (e.g., ceramics or radiation-hardened glasses), along with full vacuum, thermal-vacuum, and radiation qualification [45].  
In conclusion, the exploration of AM for fabricating complex RF components--such as horn antennas and GRIN lenses--is not only feasible but also advantageous for the communications industry. By enabling the integration of lightweight, customizable, and precisely engineered polymer structures with metalized conductive elements, AM provides a versatile platform for advanced RF device design. The ability to control material properties and topology on a fine scale, particularly for gradient-index lenses, represents a key advancement in wave manipulation and antenna performance. As the field of AM continues to evolve, its application in communications is likely to expand, supporting the development of more sophisticated, compact, and efficient systems across a range of frequencies and applications.  
Conceptualization, F.V. and C.B.; methodology, C.B.; software, A.V., F.V., and L.S.; validation, F.V., F.P., and R.K.; formal analysis, F.V.; investigation, A.V. and A.F.; resources, C.B.; data curation, A.V.; writing--original draft preparation, A.V.; writing--review and editing, C.B.; visualization, A.V.; supervision, C.B. and F.V.; project administration, F.V.; funding acquisition, C.B. All authors have read and agreed to the published version of the manuscript.  
This work has been funded by Agencia Valenciana de la Innovacion through the research project INNEST/2022/124; FEDER, EU: PID2022-136590 OB-C41/AEI/10.13039/501100011033; European Union NextGenerationEU project PRTR-C17.I1 as part of the Advanced Materials program supported by Ministerio de Ciencia e Innovacion, Generalitat Valenciana project: MAOCOM-6G, Code: MFA/2022/056 and Ministerio de Ciencia e Innovacion project PID2022-136869 NB-C33.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.