# Waveguide Manufacturing Technologies for Next-Generation Millimeter-Wave Antennas
###### Abstract  
Some recent waveguide-based antennas are presented in this paper, designed for the next generation of communication systems operating at the millimeter-wave band. The presented prototypes have been conceived to be manufactured using different state-of-the-art techniques, involving subtractive and additive approaches. All the designs have used the latest developments in the field of manufacturing to guarantee the required accuracy for operation at millimeter-wave frequencies, where tolerances are extremely tight. Different designs will be presented, including a monopulse antenna combining a comparator network, a mode converter, and a spline profile horn; a tunable phase shifter that is integrated into an array to implement reconfigurability of the main lobe direction; and a conformal array antenna. These prototypes were manufactured by diverse approaches taking into account the waveguide configuration, combining parts with high-precision milling, electrical discharge machining, direct metal laser sintering, or stereolithography with spray metallization, showing very competitive performances at the millimeter-wave band till 40 GHz. m minto the creation of PCB antennas with multi-function radiation characteristics [14; 15; 16]. However, due to relatively high-power losses associated with the use of dielectric elements, especially in planar transmission media, this technology is still far from being able to scale up to the frequencies required in the new millimeter wave systems. In contrast, waveguide-based antennas [17; 18; 19] are a well-established technology that, due to their absence of dielectric parts, can work with high powers and exhibit low loss levels. Nevertheless, the approaches employed traditionally to manufacture these kinds of antennas, involving 3D metallic pipes, have limited the creation of designs with complex geometries at very high frequencies. It is clear that planar technologies provide easier routing than do 3D pipes, whose shape was traditionally rectangular or circular [20]. Nonetheless, the development of new manufacturing technologies during recent years has opened up the possibility of building waveguides and antennas with very complex geometries that could not be built using classical approaches. This paper presents several approaches for the manufacturing of these kinds of antennas, together with state-of-the-art examples of devices built using them. First, high-precision subtractive machining is considered. Although this is a quite classical approach, it is possible to manufacture highly complex devices using it. The key idea is to segment the device into different parts that are built independently, to be assembled together subsequently. Although this approach may seem simple, the problems associated with segmentation involve a very close interaction between electrical and mechanical engineers. On one hand, from the electrical point of view, the need for more parts to be assembled implies more insertion losses and can reduce the power-handling capability of the device, while increasing the risk of passive intermodulation issues, as more flanges are needed to connect the different parts. On the other hand, a small number of parts may lead to very difficult features from the mechanical point of view, and tolerances may subsequently destroy electrical performance. This trade-off must be resolved by experienced practitioners. This paper will provide an example of a successful network implementation. Next, direct metal laser sintering (DMLS) is presented. This technique enables the printing of 3D metallic objects by using a high-power laser to bind together powdered metal particles [21]. This technique has been used recently to develop antennas and other waveguide devices in millimeter-wave frequencies [22; 23; 24] up to W-band [25]. DMLS is quite new in the antenna field.