## 1 Introduction  
Additive manufacturing (AM) by 3D-printing has increasingly spread in the last decade. This has deeply influenced methods of developing goods in a lot of application fields, allowing greater customization and speeding up the prototyping time of new devices. This is going to be very impactful in the research field for two main reasons. The first is the extremely cost-effective nature of developing prototypes with some common AM technologies, like fused filament fabrication (FFF) and Vat polymerization, including stereolithography (SLS) or digital light processing (DLP). The second reason is that AM allows for the development of devices with unconventional shapes, which could be difficult to manufacture with traditional techniques, thus enabling a lot of new and unexplored applications. These peculiarities make the framework of electromagnetic applications one of the most interesting and fertile fields of research for exploring the use of AM. This interest has been proven by the increasing number of scientific papers published on this topic. An example can be seen in Figure 1, which represents the trend of the term \"3D printed antennas\" in the last ten years, considering as reference the Google Scholar database. The reported data have been collected by using a python script by [PERSON] et al. [1]. Specifically, going deeper in analyzing some of the most relevant scientific papers regarding 3D-printed antennas, it emerges how a variety of different devices, designed for different purposes, are realizable with different 3D printing technologies. For example, considering FFF technology, in [2], an RFID reader antenna composed of four planar inverted-F antennas (PIFA) realized onto a substrate with different heights printed using a conventional polylactic acid (PLA) has been described; in [3], the same material was used to realize the substrate of a curved patch antenna, with the metallization obtained using adhesive copper tape; in [4], an acrylonitrile butadiene styrene (ABS) filament hasbeen printed to realize the substrate of a conformal array of antennas, with the conductive parts made by using copper plating technique; in [5], a polycarbonate (PC) filament has been used to print a circular horn antenna with corrugated chokes, which has then been metallized with a conductive silver ink. As for Vat-polymerization 3D printing technologies, in [6], an interesting hollow structure has been printed with SLA to realize a Yagi-Uda loop antenna utilizing liquid metal to fill the microfluidic channels; in [7], an X-band horn antenna fabricated by an SLA 3D printer in barely 3 h has been described. The metallization has subsequently been obtained by means of a conductive spray coating. In [8], a dual band UHF RFID tag composed by two sliding parts printed using DLP technology has been described and compared with a twin realized with FFF technology. Conversely, considering technologies with higher setting up costs and more stiff operative constraints, which enable the printing of conductive parts, in [9], both waveguide circuits and antennas realized with binder jetting (BJ) technology, by using metallic powder, have been described, realized, and tested; whilst in [10], direct metal laser sintering (DMLS) technology has been used to realize a wideband conical corrugated horn antenna operating between 25 GHz and 45 GHz. The aforementioned studies represent only a small part of the many potential applications of 3D printing in electromagnetics that have been explored in the last few years. Many others can be found, for example, in [11], where [PERSON] et al. made a great review of the state of the art on 3D printed antennas, by listing and categorizing the applications both for type of technology, material used, and working frequency. From this preliminary analysis, some considerations can be made on the characteristics of the different techniques. For example, metallic parts are always problematic to create and often need some further manufacturing process to be prototyped.