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.

Keywords: millimeter-wave devices; waveguide manufacturing by direct metal laser sintering; waveguide manufacturing by stereolithography; waveguide manufacturing by subtractive machining.

Figure 1

Monopulse horn antenna [22]. The three components that form the antenna are highlighted by different colors: solid red for the comparator network; dashed blue for the mode converter; and dashed-dotted green for the horn.

Figure 2

Top view of the comparator network. The rounding of the corners produced by the drill is included in the drawing, as well as the holes for inserting the screws and alignment pins. The main dimensions of the component, in millimeters, are annotated.

Figure 3

Representation of the mode converter: (a) the two waveguide parts that form the device, with the holes for screws and alignments pins visible; (b) depiction of the internal air cavities.

Figure 4

Measured (solid) and simulated (dotted) performances of the triple-radiation pattern monopulse horn antenna: (a) sum radiation pattern, $$D_{irectivity,Meas}=24.85 \mathrm{dBi}$$ ; (b) difference in azimuth radiation pattern, $$D_{irectivity,Meas}=22.66 \mathrm{dBi}$$ ; (c) difference in elevation radiation pattern, $$D_{irectivity,Meas}=22.44 \mathrm{dB}$$ ; and (d) reflection coefficient for each radiation pattern.

Figure 5

Schematic used generally to represent the direct metal laser sintering (DMLS) technique.

Figure 6

Photographs of the reconfigurable phase-shifters block built using DMLS: (a) frontal view; (b) cut view that allows observing the internal parts of the device.

Figure 7

Measured phase shift produced by one of the WRPS for different values of TS (tuning screw) penetration.

Figure 8

Measured and simulated (Sim) magnitude of the reflection coefficient at the input of one of the WRPS (the phase-shifter marked as I in Figure 6) for different values of TS (tuning screw) penetration.

Figure 9

H-plane cut ($$\varphi =0$$) of the radiation pattern produced by the waveguide array for different scanning directions $${\theta }_0$$. The solid line corresponds to the measurements and the dotted line corresponds to the simulations.

Figure 10

Initial prototypes manufactured in a commercial 3D printer and metallized with a copper coating.

Figure 11

Spray metallization scheme developed by JetMetal [47].

Figure 12

Photographs of the conformal array antenna manufactured by SLA + spray metallization: (a) whole antenna prototype; (b) slotted cylindrical waveguide detail; and (c) dual-mode feeder.

Figure 13

Conformal array antenna normalized radiation patterns: (a) simulated and measured ϕ = 0° patterns at 28 GHz; (b) simulated and measured ϕ = 90° patterns at 28 GHz; and (c) measured ϕ = 90° patterns at 26 and 30 GHz.

Figure 14

Conformal array antenna normalized radiation patterns: (a) simulated and measured ϕ = 0° patterns at 38.5 GHz; (b) simulated and measured ϕ = 90° patterns at 38.5 GHz; and (c) measured ϕ = 90° patterns at 37 and 40 GHz.